A numerical model to predict the rate of advance of the wet front along an
overheated wall was developed and tested with available experimental data. The model
shows that the predicted unsteady rate of advance of the wet front, which is in
agreement with experimental results is due to precursory cooling.
Following a Loss-of-Coolant Accident (LOCA) in a water cooled
nuclear reactor, process of fundamental importance is the rewetting
of the overheated fuel elements by an Emergency Core Cooling System
(ECCS). It is well accepted that the rate of advance of the wet
front depends upon several parameters, the most important being the
initial temperature of the overheated fuel elements cladding, the
system pressure, the heat transfer coefficient at the wet front, and
the properties of the cladding. The effect of secondary parameters,
such as the quenching liquid subcooling and flowrate, and the
precursory cooling ahead of the wet front due to the droplet-vapor
mixture, are still under investigation. The present work is a
detailed statistical analysis of available experimental data. It
uses the method of confidence interval ellipses, to investigate the
liquid flowrate effect on the rewetting rate. The results of this
analysis show that the rewetting rate increases with the liquid
flowrate only when the wet front advances in an open air environment
at atmospheric pressure, while it remains unaffected in a vapor
environment at relatively high pressures.
The results of field investigations of natural radiation exposures of the general populations in two
stable rural communities in Yugoslavia are presented. The principal emphasis was on exposures to
contemporary indoor radon but measurements of external penetrating radiation absorbed dose rates in
air were carried out in the majority of cases. In addition in a limited number of dwellings,
measurements of thoron gas concentrations were made. By means of making a series of sequential
three month radon measurements, both seasonal variations and annual average radon levels in the
dwellings were determined. Using passive alpha track detectors, individual radon and thoron indoor
concentrations as high as 9591 Bq/m3 and 709 Bq/m3 respectively were detected while absorbed dose
rates in air in the dwellings as high as 430 nGy/hr were recorded.
On the basis of these different types of measurements, assessments could be made of the integrated
natural radiation exposures being received by the populations. In addition to contemporary radon
measurements, retrospective radon exposure assessments in most of the dwellings were made on the
basis of measurements of 210Po concentrations in both surface (glass) traps and in volume (porous
materials) traps.
A description is given of the sampling strategies and protocols used in this field work. It is shown that
at least one stable rural community receiving high natural radiation exposures, has been clearly
identified and plans for future health investigations of the population there are outlined.
The Megalopolis lignite field basin
in southern Greece, with Megalopolis-A and B
lignite-fired power plants in operation (total 900 MW), has been
repeatedly investigated during the past 25 years by the Nuclear Engineering
Section of the National Technical University of Athens (NES-NTUA). The present
work aims at an integrated
radioenvironmental approach leading to the dose assessment to the public and to
the plants staff. This approach includes systematic sampling of lignite and
barren at the local lignite mines feeding the power plants and sampling of
lignite, fly-ash and bottom ash at the power plants for the determination of the
activity of the natural radionuclides 226Ra, 232Th,
40K, 234Th and 210Pb. Furthermore, the
following measurements and samplings were conducted in 25 selected sites within 10km around the power plants: soil sampling for the determination
of the above radionuclides, radon concentration and exhalation rate
measurements, soil gas radon concentration measurements, dose measurements and
calculations, determination of air-particulate matter concentration etc. The
results obtained allowed for the
mapping of the parameters studied which lead
to useful conclusions. Dosimetric calculations for the population living around
the power plants and the plants staff were also performed, based on the
suggestions of [UNSCEAR, 1982]. Coal- and lignite-fired power plants produce significant amounts of ashes, which are quite often being used
as additives in cement and other building materials. In many cases coal and lignite present high concentrations
of naturally occurring radionuclides, such as 238U, 226Ra, 210Pb, 232Th and
40K.
Moreover, during the combustion process the produced ashes are highly enriched in the above radionuclides, thus characterized
as Technologically Enhanced Naturally Occurring Radioactive Materials (TENORM). The most important naturally
occurring radionuclide in such power plant ashes is 226Ra, since it produces radon, which when exhaled
contributes significantly to the dose received by workers and the public. An extensive research project for the
determination of the natural radioactivity of lignite and ashes from Greek lignite-fired power plants is in
progress in the Nuclear Engineering Section of the National Technical University of Athens (NES-NTUA) since 1983.
From the results obtained so far it may be concluded that 226Ra radioactivity of fly-ash may, in some
cases, exceed the 1kBqkg-1 level, which is high compared to the mean 226Ra radioactivity of
surface soils in Greece (25Bqkg-1). Furthermore, the radioactivity of 210Pb in fly-ash may
reach the value of up to 4kBkg-1, depending on the sampling location inside the power plant. This paper
presents: natural radioactivity results from the analysis of the lignite fed to and the ashes produced in Greek
lignite-fired power plants, enrichment factors of natural radionuclides in the ashes and radon exhalation
measurements from fly-ash collected at different stages along the emission control system. Enrichment factor results are
being interpreted in relation to the physical properties of the investigated nuclides and the temperature and
flow parameters in the flue gas pathway. Discarded ash deposition fields in the vicinity of the power plants
are also investigated in terms of surface soil radon exhalation and soil gas radon concentration.
The use of depleted uranium (DU) in military operations causes the contamination of the target area due to DU dispersion
in the environment. Since the isotopic abundance of uranium in DU is different than that in nature, the only evidence of
DU contamination is the disruption of the natural isotopic abundance of 238U and 235U. For the
investigation of the existence of such a disruption, the accurate determination of 235U and 238U
is necessary. The Nuclear Engineering Section of the National Technical University of Athens (NES-NTUA)
uses high-resolution LEGe detectors and especially developed gamma spectroscopic analysis techniques for the determination
of 238U, 235U and subsequently for the isotopic abundance of the uranium isotopes in the sample.
Uranium 235 is determined from the analysis of the multiplet photopeak at 186 keV. DU may be detected with this
technique provided that the 238U activity of the DU is higher than ~20% of that of 238U in
the natural uranium of the sample. The analyses by NES-NTUA of surface soil samples collected well before the dispersion of
depleted uranium in Kosovo, made evident that Kosovo is an area of high natural background, with a pronounced surface
soil variation in natural uranium content, and 238U activity reaching values as high as 330 Bq kg-1.
It was also observed that disturbance of radioactive equilibrium among the nuclides of the uranium series is quite often observed
due to leaching and weathering, with the ratio of the activities of 238U and 226Ra ranging from 0.17 to 5.5.
After the military operations in Kosovo, surface soil and vegetation samples as well as DU penetrators were analysed in NES-NTUA.
Among the soil samples analysed it was found that some of those collected around a DU penetrator crater were contaminated by DU,
with 238U activity exceeding 2 kBqkg-1, and ratio of 238U/226Ra exceeding the value of 10.
In these soil samples, the natural isotopic abundance of the uranium isotopes was significantly disrupted;
this allowed for an estimation of the isotopic abundance of 235U in the dispersed DU of about 0.2%,
which agrees very well with relevant values found in the literature for DU penetrators. DU in the vegetation samples
analysed was below detection limit. The analysis of DU penetrators led to the detection 238U, 235U
and their daughters, and to an estimation of the dose-rate due to the gamma-rays emitted from the penetrator,
which reached 6.5 μSvh-1 on the surface, sloping to background at the distance of about 40 cm.
Immediately after the Chernobyl accident, a soil-sampling programme was undertaken in order to detect and quantitatively
analyse the long-lived radionuclides in the Chernobyl fallout. Soil samples (1242 in number) of 1 cm thick surface
soil were collected in Greece, during the period from May-November 1986. The samples were counted and analysed using
Ge detector set-ups. In an attempt to proceed to the mapping of the long-lived radionuclides detected, an in-house
Unix-based Data Base/geographical information system (DBGIS) was developed. Prior to mapping multifractal analyses of
the deposition pattern for each radionuclide detected were performed. In the present work an analysis of the results
of the deposition of 137Cs, 134Cs, 144Ce, 141Ce, 125Sb, 110mAg,
106Ru, The Megalopolis lignite field basin is
located in the centre of the Peloponese peninsula in southern Greece. Two
lignite-fired power plants are in operation in this region: Megalopolis-A
(600MW – 3 units) since the early 70's and Megalopolis-B (300MW – 1 unit)
since the early 90's. An extensive research project for the determination of
the natural radioactivity of lignite and ashes from the Megalopolis power
plants started in the Nuclear Engineering Section of the National Technical
University of Athens (NES-NTUA) in 1983. The project has evolved to an
integrated radioenvironmental survey of the Megalopolis lignite field basin
area. The present work aims at the presentation of the
radioenvironmental
survey of the fly-ash deposits in the vicinity of the power plants. The power
plants produce over 2 million metric tonns of fly-ash annually, which is
primarily disposed off in deposits located mainly at exhausted lignite mines.
These deposits are in the form of ash layers several meters thick, which are
then covered by a layer of soil. The disposed fly-ash has a 226Ra
content which sometimes exceeds 1 kBqkg-1, which is very high
compared to the mean 226Ra radioactivity of surface soils in
Greece (25 Bqkg-1). Results regarding (a) γ-dose rate, (b) radon
concentration in the ambient air, (c) soil radon exhalation rate and (d) soil
gas radon concentration are reported from systematic field measurements at
three deposit sites. Repeated measurements under various environmental conditions
have been carried out, in order to estimate the variability of the radon
related quantities. In addition, soil sampling of the surface and 0-80 cm
layer has been conducted at the deposits to allow for the determination of
the activity of natural radionuclides, namely 226Ra, 232Th,
40K, 234Th and 210Pb. The radiological
characterization of the fly-ash deposits obtained through these results is
compared to the natural radioactivity background in the wider Megalopolis
area, using additional results of a previous similar survey by NES-NTUA [1].
It can be concluded that, from the radiological point of view, the
Megalopolis fly-ash deposits do not differ significantly from the rest of the
Megalopolis lignite field basin, despite the fact that most of the
underground soil layers consist of fly-ash with high 226Ra
content. A possible explanation for this might be that radon emanation from
the fly-ash layer is as low as radon emanation from natural soil due to
fly-ash crystallization process in the power plant furnace. This explanation
is currently under experimental investigation in the NES-NTUA Laboratory.
Furthermore, the comparison of results from different aged deposition fields
concludes that aging and restoration processes in the deposition fields, such
as tree cultivation and agriculture have a positive effect to radon related
radiological parameters. [1] P.K.Rouni, N.P.Petropoulos, M.J.
Anagnostakis, E.P. Hinis and S.E.Simopoulos, "Radioenvironmental survey
of the Megalopolis lignite field basin", The Science of the Total
Environment, 272(2001); 261-272. Coal and lignite fired power plants produce significant amounts of ashes, which are quite often being used
as additives in cement and other building materials. In many cases coal and lignite present high
concentrations of naturally occurring radionuclides, such as 238U, 226Ra, 210Pb, 232Th
and 40K. Moreover, during the combustion process the produced ashes are highly enriched in the above radionuclides,
thus characterized as Technologically Enhanced Naturally Occurring Radioactive Materials (TENORM).
The most important naturally occurring radionuclide in such power plant ashes is 226Ra, since it produces radon,
which when exhaled contributes significantly to the dose received by the workers and the public. An extensive research
project for the determination of the natural radioactivity of lignite and ashes from Greek lignite fired power plants
is in progress in the Nuclear Engineering Section of the National Technical University of Athens (NES-NTUA) since 1983.
From the results obtained so far it may be concluded that 226Ra radioactivity of fly-ash may,
in some cases, exceeds the 1kBqkg-1 level, which is high compared to the mean 226Ra radioactivity
of surface soils in Greece, which is 25Bqkg-1. Furthermore, the radioactivity of the volatile 210Pb
in the fly-ash may reach the value of up to 4kBkg-1, depending on the sampling location inside the power
plant. The enrichment factor depends upon the specific nuclide physical properties as well as on other factors.
In this paper it will be presented: natural radioactivity results from the analysis of the lignite's feeding
and the ashes produced in greek lignite-burning power plants, enrichment factors of natural radionuclides in
the ashes and radon exhalation measurements from fly-ash collected at different stages along the emission control
system of the power plants. Similar results will be presented for building materials fabricated using fly-ash. Finally,
an estimation of the radiological consequences due to the fly-ash releases in the vicinity of a lignite-burning
power plant, and the use of fly-ash in building materials production will be presented.
This work presents a method developed at the NES-NTUA to generate radon-in-water solutions of known concentration that
can easily be applied in a laboratory with access to a Radon-in-air calibration facility. The method has been proven to
be accurate enough for the solution produced to be usable as a secondary standard, traceable to within 10% of
the calibration of the original Radon source. This fact, as well as other attractive features such as low
running cost and ease of use, makes it appropriate for purposes such as quality control, intercalibration of
instruments and laboratory intercomparison.
High concentrations of natural radionuclides in building materials can result in high dose rates indoors,
from both internal and external exposure. In dose calculations, the main radionuclides of interest are
226Ra, 232Th and 40K. Usually much attention is paid to 226Ra due to
Rn-222 exhalation and the subsequent internal exposure. Other radionuclides of the uranium series such
as 238U and 210Pb, emitting low energy photons are not usually determined and an assumption of radioactive equilibrium is made. The above assumption is seldom
checked mainly because of the difficulties in the γ-spectroscopic analysis of low energy photons.
For the determination of radionuclides emitting low-energy photons, in samples like building materials
where intense self-absorption of the photons exists, a method for self-absorption correction has been developed.
The method needs as input the linear attenuation coefficient μ for the material under analysis. This paper presents:
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Journal of Environmental Radioactivity 5:379-389, 1987
NATURAL RADIOACTIVITY RELEASES FROM LIGNITE POWER PLANTS IN GREECE
S.E.Simopoulos and M.G. Angelopoulos
Nuclear Engineering Section, National Technical University of
Athens, 15780 Athens, Greece
In Greece, power stations burning lignite from two large deposits,
in the regions of Megalopolis and Ptolemais, play an important role
in meeting the energy needs of the country. The investigation
reported
here
deals with the determination of Ra-226, Ra-228 and
K-40 concentrations in the lignite feeding two power units in
Megalopolis and in the product ash. Systematic sampling allowed
evaluation of mean representative concentrations and estimation of
the resulted atmosphere discharges of radioactivity. Furthermore,
statistical analysis has shown that, at the 95% confidence level
essentially all Ra-226 from the lignite feeding each unit is
accounted for in the ash. The results of both the present and
previous investigations on two units burning lignite from the
Ptolemais deposit show that electricity generation from Greek
lignites is associated with radioactivity discharge data from the
literature.
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Proceedings of the 1st Balkan Scientific Conference on
Environmental Protection in the Balkans, Vol. 2, pp. 334-344,
September 20-23, 1988,
Varna, Bulgaria
ELECTRICITY GENERATION AND ITS ASSOCIATED RADIOLOGICAL IMPACT TO THE ENVIRONMENT
S.E.Simopoulos and M.G. Angelopoulos
Nuclear Engineering Section, National Technical University of
Athens, 15780 Athens, Greece
Nuclear power stations during normal or abnormal operation, as well
as fossil fuel power stations release radioactivity to the
environment. In the former case and mainly during an abnormal
operation, these releases may affect even regions at great distances
from the site of the station. In the latter case the radiological
impact to this environment is of limited extent and is due to the
trace quantities of the naturally occuring U-238 and Th-232, their
associated daughter products and K-40, which are contained in fossil
fuels. These radionuclides are released to the environment either
directly, through the stack, or indirectly, from fly and bottom ash
storage and from the use of fly ash in building materials.
The purpose of this presentation is to report the concentrations of
Ra-226, Ra-228 and K-40 determined in the lignite feeding four power
units of the Greek grid and its product ashes. Furthermore, the
atmospheric discharges of the above isotopes from these units as
well as their radiological significance is evaluated. Finally, some
remarks relevant to the evaluation of mean representative
concentration and to the estimation of the resulting atmospheric
discharges of radioactivity, are also included.
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Appl. Radiat. Isot. Vol. 40, No. 7, pp. 607-613, 1989,
Int. J. Radiat. Appl. Instrum. Part A
SOIL SAMPLING AND Cs-137 ANALYSIS OF THE CHERNOBYL FALLOUT IN
GREECE
S.E.Simopoulos
Nuclear Engineering Section, National Technical University of
Athens, 15780 Athens, Greece
A total of 1242 samples of soil, collected over Greece, during the
period May-November 1986 were counted and analysed for Cs-137 from
Chernobyl fallout. The counting was performed using a NaI detector
on line to a microcomputer; morover, 252 of the samples were also
analysed using Ge detectors, for inter-comparison and also for the
assessment of other long-lived isotopes in the fallout. The results
show that Cs-137 fallout from Chernobyl presents a remarkable
geographical variability. The evaluated ground activity due to
Cs-137 deposition ranges between 0.01 and 137 kBq/m².
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Health Physics, Vol. 61, No. 6 (December), pp. 885-888, 1991
EFFECT OF DIETARY INTAKE ON THE Cs-137 RETENTION MODEL
A. Louizi and C. Proukakis
Department of Medical Physics, School of Medicine,
Athens University, 11527 Athens, Greece
S.E.Simopoulos and M.G.Angelopoulos
Nuclear Engineering Section, Mechanical Engineering Dept.,
National Technical University of Athens, 15780 Athens, Greece
Whole-body counting measurements were conducted to monitor the
Cs-137 biological half life of 14 individuals in Athens during the
period June 1988 to June 1989. The results and the solution of a
Cs-137 retention model showed that the individuals examined were
receiving 0 - 3.7 Bq/d of Cs-137 through the food chain during the
period investigated.
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ASME International Conference,
Analysis of Thermal and Energy Systems, pp. 983-995,
June 3-6, 1991, Athens
INVESTIGATION OF THE LIQUID FLOWRATE EFFECT ON THE REWETTING RATE
A.P. Konstantaropoulou and S.E.Simopoulos
Nuclear Engineering Section, Mechanical Engineering Dept.,
National Technical University of Athens, 15780 Athens, Greece
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Workshop on the
LONG TERM FOLLOW UP OF THE CHERNOBYL DISASTER,
World Health Organization,
International Union Against Cancer,
Hellenic Cancer Society,
pp. 157-171, December 6-8, 1991, Athens
DEPOSITION MEASUREMENTS IN EUROPE AFTER THE CHERNOBYL ACCIDENT
AND COMPARISON WITH THE GREEK "NTUA DATA SET"
S.E.Simopoulos and M.G.Angelopoulos
Nuclear Engineering Section, Mechanical Engineering Dept.,
National Technical University of Athens, 15780 Athens, Greece
Fission product deposition data, from the Chernobyl reactor accident,
have been compiled by the Commission of the European Communities
and put together as part of the Radioactivity Environmental Monitoring
(REM) programme. Most of these data originate from surface soil
sampling and analysis for longer-lived activity with emphasis to that
due to Cs-137. According to this compilation, of 3233 data, 1460 of
which come from the Greek NTUA soil sampling programme, the Cs-137
cumulative deposition ranges between 261 to less than 1 kBq/m², while the
ratio Cs-134/Cs-137 is always close to 0.5. The data provided by the
Greek NTUA soil sampling programme, which is considered by the CEC as
"intensive and systematic", show that the mean value of the Cs-137
deposition in Greece (7.3 kBq/m² - 1242 samples) was not as high as
mean values of subregions of other EC countries, such as Southern Germany
(14 kBq/m² - 98 samples) and Northern Italy (15 kBq/m² - 29 samples).
The maximum observed cumulative deposition of Cs-137 is 149 kBq/m²
detected near the city of Karditsa in Central Greece. The high resolution
gamma spectrographic analysis of the above data set, provides also
information about other longer-lived fission products in the fallout,
the most important of which is Ru-103 with maximun observed cumulative
deposition 337 kBq/m² detected near the city of Naoussa, in
Northern Greece.
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Proceedings of the 1st Mediterranean Congress on Radiation Protection,
pp. 240-244, April 5-7, 1994, Athens
MEASUREMENTS OF NATURAL RADIOACTIVITY IN GREEK BUILDING MATERIALS
A. Louizi and C. Proukakis
Department of Medical Physics, School of Medicine, Athens University,
11527 Athens, Greece
N.P.Petropoulos, M.J.Anagnostakis, S.E.Simopoulos, and M.G.Angelopoulos
Nuclear Engineering Section, Mechanical Engineering Dept.,
National Technical University of Athens, 15780 Athens, Greece
Building materials and paints may release radon or cause direct
radiation exposure because of their content of radium, thorium and
potassium. Concrete, brick and granite-stone walls may produce
significant external dose rates nGy/hr and -furthermore-
give rise to radon exhalation rates of up to 50 Bq/m². A wide research
project to investigate the radioactive behaviour of Greek building
materials and structural modules has been set-up and is still in
progress. In the framework of this project ample specimens of commonly
used building materials have been collected randomly over the country.
The specimens were dried under ambient temperature and then pulverised
to less than 90 µm; finally, the water content of all specimens was
determined before being hermetically sealed in 0.282 L cylindrical plastic
boxes, covered with a film of epoxy resin to limit - as far as possible -
escape of radon. Each box was analysed after secular equilibrium of
Ra-226 and Th-232 with their decay products was obtained, using high
resolution Ge-detectors setups; activity concentrations were averaged
from photopeaks at several energies. The results obtained show that the
natural radioactivity content of the various Greek building materials
examined is very low. Only a few specimens of cement and clay bricks
present a rather high Ra-226 concentration up to 144 and 48 Bq/kg
respectively. However, these values are within the range of similar
materials used in other European countries.
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Proceedings of the 1st Mediterranean Congress on Radiation Protection,
pp. 252-267, April 5-7, 1994, Athens
MINI RADON HOUSE : A PROTOTYPE CONTAINER FOR THE MEASUREMENT
OF RADON EXHALATION FROM BUILDING MATERIALS AND STRUCTURAL MODULES
A. Louizi and C. Proukakis
Department of Medical Physics, School of Medicine, Athens University, 11527 Athens, Greece
N.P.Petropoulos, E.P.Hinis, S.E.Simopoulos and D.J.Leonidou
Nuclear Engineering Section, Mechanical Engineering Dept., National Technical University of Athens, 15780 Athens, Greece
Radon in indoor air is partly due to its exhalation from
building materials. It is therefore important to develop techniques
for measuring the exhalation rates from such materials and also
from their structural modules, such as test walls and concrete
slabs.
These techniques could be also employed for estimating
the remediating effect of coatings used as radon barriers
on walls, floors and ceilings. For this purpose an air-tight, N2
filled, 1m³
steel container has been constructed, in which
raw building materials and prototype structural modules of volume
not exceeding 100 L are enclosed for evaluating
their exhalation rate. The environment is conditioned by a
heating unit, a humidifier and an air blower, in order to
control temperature and humidity
over the range 12-45 °C and 15-99% respectively;
an aerosol generating system is used to produce particles.
The container is equipped with several monitoring transducers on line
to data acquisition computers.
Radon progeny radiation is continuously monitored in-situ
via a 2x2'' Am-doped NaI detector stabilised for spectrum
shifts.
Several port holes located on the upper and side walls, allow for
grab sampling of the radon progeny on high efficiency filters by
pumping approximately 15% of the enclosed N2 through the container
using accurate flowrate control. The filters are then analysed
using high-resolution gamma and alpha spectrographic techniques. The
container is calibrated
with a Ra-226 source of a nominal activity of 102.8 kBq,
shielded in a small metal drum with a lid which can be remotely
opened or closed.
Concentration of the homogeneously distributed radon can be
regulated up to 100 kBq/m³ by appropriately closing or opening
the drum. The efficiency of the container
has been experimentally determined ranging within 5-30%
depending on the environmental conditions inside it.
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Proceedings of
"INDOOR AIR, An Integrated Approach, International Workshop"
, pp. 131 - 134,
November 27 - December 1, 1994,
Gold Coast, Australia
NATURAL RADIOACTIVITY CONTENT AND RADON EXHALATION RATES
OF GREEK BUILDING MATERIALS
A. Louizi and C. Proukakis
Department of Medical Physics, School of Medicine,
Athens University, 11527 Athens, Greece
N.P.Petropoulos and S.E.Simopoulos
Nuclear Engineering Section, Mechanical Engineering Dept.,
National Technical University of Athens, 15780 Athens, Greece
Greek building materials were analysed for natural radioactivity
(Ra-226, Th-232 and K-40) which, according to the results obtained,
is low with the exception of a few specimens of cement and clay
bricks with Ra-226 concentrations up to 147 and 48 Bq/kg respectively.
The radon exhalation rate of the same materials has been evaluated
using an air-tight 1m³ steel container. The container environment
is conditioned by a heating unit and a humidifier, in order to
control temperature and humidity over the range 12-45 °C and 15-99%
respectively. A ±50 mbar differential pressure transducer is
used for recording pressure changes inside the container, which is
also equipped with an aerosol generating system. Radon progeny
radiation is continuously monitored in-situ via a 2x2'' Am-doped
NaI detector stabilised for spectrum shifts. Furthermore, grab
sampling on high efficiency filters analysed using high-resolution
gamma and alpha spectrometry is also conducted. The exhalation rate
of the above Greek building materials already analysed range
between 3-20 µBq/(kgs). Moreover, brick walls and concrete slabs
constructed using these materials present exhalation rates
between 2-3 mBq/(m²s).
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NRE VI, International Symposium, June 5-9, 1995, Montreal,
ENVIRONMENT INTERNATIONAL, Vol. 22, Suppl. 1, pp. S3-S8,1996
NATURAL RADIOACTIVITY MAPPING OF GREEK SURFACE SOILS
M.J.Anagnostakis, E.P.Hinis, S.E.Simopoulos, and M.G.Angelopoulos
Nuclear Engineering Section, Mechanical Engineering Dept.,
National Technical University of Athens, 15780 Athens, Greece
A total of 1440 samples of soil, collected across Greece from the
1 cm surface layer, were analysed for natural radioactivity (Ra-226,
Th-232 & K-40). The samples were air-dried and then hermetically
sealed in 0.282 L plastic boxes covered with a film of epoxy resin
to ensure that no gases escape from them. Secular equilibrium of
Ra-226 and Th-232 with their decay products was obtained before the
samples were analysed using high resolution Ge gamma-ray detectors.
A Unix-based in-house built complex Data Base/Geographical Information
System (DBGIS) was used to analyze the data and present them in
map
form. The analysis of a second 1 cm thick sample, collected at several
sites at a depth of 10 cm, led to the statistically justified conclusion
that the natural radioactivity content of the surface and of 10 cm deep
soil layers do not significantly differ. According to these results
the natural radioactivity content of Greek surface soils is rather low
(mean ± standard deviation in Bq/kg):
and entails a gamma-ray dose rate outdoors equal to 40 nGy/h.
A statistical analysis showed that only 90 samples, collected at
67 locations, have Ra-226 content exceeding their mean value
by more than 1.65 std. dev. The Ra-226/Th-232 and Ra-226/K-40
concentration ratios were equal to (mean value ± % std. dev.)
1.10 ± 44% and 0.06 ± 56%, respectively.
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NRE VI, International Symposium, June 5-9, 1995, Montreal,
ENVIRONMENT INTERNATIONAL, Vol. 22, Suppl. 1, pp. S369-S373, 1996
Cs-137 CHERNOBYL FALLOUT IN GREECE
AND ITS ASSOCIATED RADIOLOGICAL IMPACT
N.P.Petropoulos, E.P.Hinis, and S.E.Simopoulos
Nuclear Engineering Section, Mechanical Engineering Dept.,
National Technical University of Athens, 15780 Athens, Greece
Right after the Chernobyl reactor accident a systematic
soil sampling and analysis programme has been undertaken by the
Nuclear Engineering Section of the National Technical
University of Athens in order to detect and quantitatively
analyse the long-lived isotopes in the Chernobyl
fallout in Greece. In the frame of this programme, 1242 soil
samples of 1cm thick surface soil were collected over Greece
during the period May - November 1986. The samples were counted
and analysed using Ge-detector setups for fission products from
the Chernobyl fallout, which led to the
mapping of Cs-137
deposition in the form of a five-class histogram, extending
between 0 - 150 kBq/m², with boundaries defined by isolines of
5, 15, 35, 65 & 150 kBq/m². To investigate the radiological
impact of the Cs-137 fallout on the Greek population, the NEA/OECD
computer code PABLM was run using as input the above isoline data.
According to the results obtained, the total body collective
effective dose commitment of the Greek population is estimated to
340 manSv over the first year after the accident and 8800 manSv over
a period of 40 years. Concerning the 6000 inhabitants within the
65 kBq/m² isoline the results are 2 manSv over the first year after
the accident and 55 manSv over a period of 40 years. The above
radiological impact was further compared to that due to fly ash
releases from the Ptolemais Lignite Power Plants, in northern Greece.
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NRE VI, International Symposium, June 5-9, 1995, Montreal,
ENVIRONMENT INTERNATIONAL, Vol. 22, Suppl. 1, pp. S375-S377,1996
NATURAL RADIOACTIVITY CONTENT OF GREEK CIGARETTES
S.Katsanevakis, N.P.Petropoulos, E.P.Hinis and S.E.Simopoulos
Nuclear Engineering Section, Mechanical Engineering Dept.,
National Technical University of Athens, 15780 Athens, Greece
A.Louizi and C.Proukakis
Department of Medical Physics, School of Medicine,
Athens University, 11527 Athens, Greece
Tobacco from Greek cigarettes was analysed for natural radioactivity;
according to the results already obtained the concentrations of both
Ra-226 and Th-232 are less than 13 Bq/kg, while that of K-40 is
relatively high, up to 1250 Bq/kg.
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NRE VI, International Symposium, June 5-9, 1995, Montreal,
ENVIRONMENT INTERNATIONAL, Vol. 22, Suppl. 1, pp. S93-S99, 1996
AN EXPERIMENTAL-NUMERICAL METHOD FOR THE EFFICIENCY CALIBRATION
OF LOW ENERGY GERMANIUM DETECTORS
M.J.Anagnostakis and S.E.Simopoulos
Nuclear Engineering Section, Mechanical Engineering Dept.,
National Technical University of Athens, 15780 Athens, Greece
Several radionuclides emit significant gamma rays at energies below 80
keV, which in many cases are essential for their detection in
radioenvironmental assays. The gamma spectroscopic analysis at this
energy region is conducted using planar Low Energy Germanium detectors,
with high and almost constant efficiency in the energy region between
20 and 80 keV. When analysing solid and liquid samples, using these
detectors, the count rate is highly affected by the intense
self-absorption of the low energy photons. Thus, the difference of the
absorption properties between the calibration source and the sample
requires the introduction of an efficiency correction factor.
A method which is applicable for cylindrical geometries was adapted
for the determination of the above correction factor using a newly
developed experimental-numerical technique and a FORTRAN program.
This program, using as input the source-to-detector geometry and
the values of the linear attenuation coefficient (µ) of both the
calibration source and the material to be analysed, calculates
the efficiency correction factor. The value of the linear attenuation
coefficient (µ) needed for this calculation is being experimentally
estimated for each material to be analysed. The technique has been
cross-checked using standard materials. According to the results
obtained, in the case of surface soil samples, lignite and fly ash
values ranges from 0.2 to 0.9 cm¯¹ and leads to efficiency
correction factors - for the geometry used and a 4M HCl mixed
radionuclide calibration source - in the range of 0.5 to 1.2 for the
photons emitted by Pb-210 at 46.52 keV and Am-241 at 59.54 keV. The
correction factor in the case of 185.99 keV photons is slightly lower
than 1.0, even for the most absorbing of the materials analysed.
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Proceedings of the 1st Conference of the Yugoslav Nuclear Society (YUNSC '96), October 7-9, 1996, Belgrade (in press)
GEOGRAPHICAL MAPPING AND ASSOCIATED FRACTAL ANALYSIS
OF THE LONG-LIVED CHERNOBYL FALLOUT ISOTOPES IN GREECE
N.P.Petropoulos, M.J.Anagnostakis, E.P.Hinis and S.E.Simopoulos
Nuclear Engineering Section, Mechanical Engineering Dept.,
National Technical University of Athens, 15780 Athens, Greece
Right after the Chernobyl accident, a soil sampling programme
has been undertaken by the Nuclear Engineering Section of the
National Technical University of Athens in order to detect and
quantitatively analyse the long-lived isotopes in the Chernobyl fallout.
1242 soil samples of 1cm thick surface soil were collected over Greece
during the period May - November 1986. The samples were counted and
analysed using Ge detector setups. The Cs-137 fallout data have
already been graphically presented; this analysis led to the mapping of
Cs-137 deposition in the form of a four-class histogram, extending
between 0-150 kBqm¯¹. In an attempt to improve this analysis and also
to extend it to other isotopes in the fallout an in-house built Unix-based
Data Base/Geographical Information System (DBGIS) was developed.
Multifractal analyses of the deposition patterns have also been performed by
the use of relevant methods. In the present work, the deposition of
Cs-137,
Cs-134,
Ce-144,
Ce-141,
Sb-125,
Ag-110m,
Ru-106,
Ru-103,
Zr-95 and
Mn-54 in the form of contour histograms is presented and
the results of the associated fractal analysis is communicated.
The maximum detected values of the above mentioned isotopes are
149.5±0.1, 76.1±0.1, 32.9±0.2, 46±2,
4.56±0.02, 7.98±0.02,
79.1±0.4, 337±2, 20.1±0.2 and
3.02±0.02 kBqm¯¹ respectively.
Furthermore, a statistical technique to compare contour mappings is
introduced and applied to explain the differences in the mappings of the
above isotopes.
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Proceedings of the 1st Conference of the Yugoslav Nuclear Society (YUNSC '96), October 7-9, 1996, Belgrade (in press)
RADIOLOGICAL IMPACT OF THE LONG-LIVED CHERNOBYL FALLOUT ISOTOPES IN GREECE
M.J.Anagnostakis, N.P.Petropoulos, E.P.Hinis and S.E.Simopoulos
Nuclear Engineering Section, Mechanical Engineering Dept.,
National Technical University of Athens, 15780 Athens, Greece
1242 soil samples of 1cm thick surface soil were collected over Greece
during the period May - November 1986. The samples were counted and
analysed which led to detailed mappings of the depositions of Cs-137,
Cs-134, Sb-125, Ag-110m, Zr-95, Ce-141, Ce-144,
Ru-103, Ru-106 and Mn-54. The deposition mappings of the
fission products Cs-137, Cs-134, Sb-125, Ce-144 and
Ru-106 allowed the localization of the three most contaminated areas
of the country, near the city of Karditsa (lat. 39.556°,
long. 21.918°), about the city of Trikala (lat. 39.553°,
long. 21.808°) and that about the city of Naoussa (lat. 46.634°,
long. 22.091°). The Cs-137 deposition in those areas
ranges between 65 - 150 kBqm¯². The geographical mean of Cs-137
deposition all over Greece was estimated to 8±9 kBqm¯². Furthermore,
these deposition mappings can be used for the investigation of the
accident's radiological impact on the Greek population. For this
reason a computer code was developed to calculate
the dose due to external irradiation ought to field deposition and
the dose due to the ingestion of contaminated food.
The present work communicates the radiological impact
on the Greek population due to the accumulated effect of long-lived fallout
isotopes. The dosimetric calculations are reported for a variety of
radionuclides and exposure pathways. According to the results obtained, the
committed effective dose due to ingestion, over a period of 50 years,
of the average exposed 20 year old adult in Greece, who had been consuming
contaminated food during the first year after the accident is
estimated to about 548 µSv. The committed effective
dose of the average exposed 20 year old adult due to external
irradiation is estimated to 67 µSv for the first
year after the accident and to 917 µSv for a period of 50 years.
The committed effective dose due to ingestion, over a period of 50 years,
of the maximum exposed 20 year old adult in the most contaminated areas of
central and northern Greece, who had been consuming highly contaminated
food during the first year after the accident is estimated to about
5.4 mSv. The committed effective dose of the
maximum exposed 20 year old adult, due to external irradiation, is
estimated to 0.7 mSv for the first year after the accident, and to
10.3 mSv over a period of 50 years.
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Proceedings of the 1st Conference of the Yugoslav Nuclear Society (YUNSC '96), October 7-9, 1996, Belgrade (in press)
EXPERIMENTAL INVESTIGATION OF THE REWETTING PROCESS AT LOW STEAM PRESSURES
E.P.Hinis and S.E.Simopoulos
Nuclear Engineering Section, Mechanical Engineering Dept.,
National Technical University of Athens, 15780 Athens, Greece
The rewetting of the overheated water cooled nuclear reactor fuel rods
after a Loss-of-Coolant-Accident, which is defined as the re-establishment
of a water film on the hot rod surfaces, is an important process for
the safety of nuclear reactors. Several water
experiments have been carried out to investigate the rewetting
phenomena and to predict the liquid film behaviour either at
atmospheric conditions or in a steam environment. Yet, there seems to
be a scarcity of experimental data for the very important low
pressure range from 2 to 7 bars with parameters the liquid film
flowrate and the subcooling. An experimental facility to simulate two-phase
low-pressure water flow phenomena has been designed, constructed and
employed to investigate the rewetting process of hot surfaces in a
water-steam environment at pressures in the above range, as well as at
atmospheric conditions; the facility is on-line interfaced to
computers which control its operation and undertake all the data
acquisition tasks. The present paper describes
the experimental work aimed at studying the wet front propagation along
a stainless steel fuel rod in a top-flooding saturated water-steam
environment in the pressure range 1 - 7 bars, under various
initial wall temperatures up to 550 °C and at a liquid flowrate of
1Lmin¯¹. Following the experimental results a correlation has been
derived to predict the rewetting rate as a function of pressure and
initial wall temperature. This correlation agrees well with formerly
proposed correlations at higher pressures by several
other investigators, thus permitting to extend their validity down
to the pressure of 1 bar. Furthermore, a numerical method is introduced to
experimentally evaluate the wet front position along the rod.
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Proceedings of the 1st Conference of the Yugoslav Nuclear Society (YUNSC '96), October 7-9, 1996, Belgrade (in press)
COMPUTER CODES IN NUCLEAR ENGINEERING
S.E.Simopoulos
Prof. of Nuclear Engineering,
National Technical University of Athens, 15780 Athens, Greece
Nuclear data refer to all the physical constants characterising nuclear
fuel behaviour and that of the other materials under the effect of
radiation so as to assess their contribution to the nuclear reaction.
Likewise, computer programs and codes are the mathematical tools used
for solving these problems through computer simulation of the operation
of an installation or piece of equipment, which offers great potential
for plant design, technical and economic optimisation and safety
studies. More systematic analyses can be conducted and there is often no
further need to undertake expensive trials using large-scale equipment.
However, these concerns are leading to increasingly complex computer
programs which require more and more powerful computers. On the other
hand, in order to explore these possibilities computer codes must be
adjusted, tested and, above all, homogeneous approaches must be found to
ensure mutual compatibility of the codes and to maintain exchange
opportunities among scientists. This is the purpose of the co-operation
undertaken in large benchmark centres. The concept of a scientific data
centre was at its origin very similar to that of a specialised library:
it should collect and compile computer codes and numerical data, carry
out limited verification and supply the information selectively in
response to user requests. Furthermore, data centres play an important
role in coordinating national efforts and in helping to avoid unnecessary
duplication of work.
Computer codes are distributed internationally by a network of three
data centres: Energy, Science and Technology Software Centre (Oak Ridge,
USA); Radiation Shielding Information Centre (Oak Ridge, USA); NEA Data
Bank (serves OECD countries except US and Canada, also serves non-OECD
countries on behalf of IAEA). Countries providing copies of nuclear
energy software prefer to retain control of its distribution: the above
three centres provide users with the assurance of a well-defined version
of each code and originators with the assurance that their wishes will
be respected.
The OECD Nuclear Energy Agency Data Bank (NEADB) provides, in
collaboration with the code centres in the United States, a service to
its Member Countries, offering computer programs covering the full chain
of computation needed for performance prediction and assessment of
nuclear facilities. It also has service arrangements with IAEA.
The Data Bank serves about 430 accredited institutions in the
participating countries. The current collection of tested codes amounts
to about 1500 packages, which is refreshed by the addition of about 100
new codes -or new version- each year; they fall into several
categories of particular interest to nuclear engineers and physicists.
Over the last few years, between 1500 and 1700 code requests have been
answered each year, by sending both the source code and ample
documentation. A recent development is the availability of versions of
many of the most frequently requested codes for mainframe computers,
adapted for personal computers.
There exist several electronic ways to access the NEA Data Bank
Services: by e-mail, by anonymous ftp, by telnet and by WWW.
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Radon in the Living Environment,
Athens, 1923 April 1999
INTEGRATED NATURAL RADIATION EXPOSURE STUDIES IN STABLE YUGOSLAV
RURAL COMMUNITIES
Z.S. Zunic
Radiation Medicine Department, Institute of Nuclear Sciences "Vinca"
P.O. Box 522, 11001 Belgrade, Yugoslavia.
J.P. McLaughlin, C. Walsh
Physics Department, University College Dublin, Belfield, Dublin 4, Ireland.
A. Birovljev
Environmental Protection Department, Norwegian Radiation Protection Authority,
P.O. Box 55, N1345, Osteras, Norway.
S.E. Simopoulos
Nuclear Engineering Section, Mechanical Engineering Department,
National Technical University of Athens, 15 780 Athens, Greece.
B. Jakupi
Physics Department, Faculty of Natural Sciences and Mathematics,
Vidovdanska bb, 38 00 Pristina, Yugoslavia.
V. Gordanic
Geoinsitute, Rovinjska 12, 11000 Belgrade, Yugoslavia.
M. Demajo
Radiation Medicine Department, Institute of Nuclear Sciences "Vinca"
P.O. Box 522, 11001 Belgrade, Yugoslavia.
F. Trotti
Venetian Reference Laboratory for Environmental Radioactivity,
CRRARPAV, Verona CRRPoliclinico B. Roma, Via Velle Menegone 3234 Verona, Italy.
R. Falk
SSI, Stockholm, Sweden.
H. Vanmarcke, J. Paridaens
SCKCEN, Boeretang 200, B2400 Mol, Belgium.
K. Fujimoto
Human Radiation Environment Division, National Institute of Radiological Sciences,
491 Anagawa, Inageku, Chiba, 2638555, Japan.
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Radon in the Living Environment,
Athens, 1923 April 1999
RADIOENVIRONMENTAL SURVEY OF THE MEGALOPOLIS
LIGNITE FIELD BASIN
P.K.Rouni, N.P.Petropoulos, M.J.Anagnostakis, E.P.Hinis and S.E.Simopoulos
Nuclear Engineering Section, Mechanical Engineering Dept.
National Technical University of Athens, 157 80 Athens, Greece
The Megalopolis lignite field basin in southern Greece, with Megalopolis-A and B lignite-fired
power plants in operation (total 900 MW), has been repeatedly investigated during the past 25
years by the Nuclear Engineering Section of the National Technical University of Athens (NES-NTUA).
The present work aims at an integrated radioenvironmental approach leading to the dose
assessment to the public and to the plants staff. This approach includes systematic sampling of
lignite and barren at the local lignite mines feeding the power plants and sampling of lignite, fly-ash
and bottom ash at the power plants for the determination of the activity of the natural
radionuclides 226Ra, 232Th, 40K, 234Th and 210Pb.
Furthermore, the following measurements and samplings were conducted in 25 selected sites within
10km around the power plants: soil sampling
for the determination of the above radionuclides, radon concentration and exhalation rate
measurements, soil gas radon concentration measurements, dose measurements and calculations,
determination of air-particulate matter concentration etc. The results obtained allowed for the
mapping of the parameters studied which lead to useful conclusions. Dosimetric calculations for
the population living around the power plants and the plants staff were also performed, based on
the suggestions of [UNSCEAR, 1982].
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Radon in the Living Environment,
Athens, 1923 April 1999
THE EFFECT OF HUMIDITY ON THE RADON COUNTING EFFICIENCY OF
INTEGRATED INSTRUMENTS
N.P.Petropoulos, E.P.Hinis, S.E.Simopoulos
Nuclear Engineering Section, Mechanical Engineering Dept.
National Technical University of Athens, 15780, Greece
Four commercially available integrated radon concentration measurement instruments, produced by
the same manufacturer in the period between 1996 to 1998, have been tested to study the effect of
absolute humidity on the radon counting efficiency. All four devices use high efficiency dRAM
cells semiconductor sensor chips for alpha particle detection. The chips are located inside a
measurement chamber, which is separated from the ambient air by a filter. Ambient air is
continuously or quasi-continuously pumped through this filter into the chamber, in order to prevent
the input of radon decay products and other solid isotopes along with the incoming air stream. Any
radon inside the chamber decays to 218Po, which becomes positively charged by ionisation effects.
The 218Po progeny is being forced to the chip detectors by a high voltage electrical field. The alpha
particles emitted by 218Po penetrate the detector and they are registered as electrical pulses. Single
channel analysis processing ensures that pulses of different heights, due to other radon and/or
thoron daughters present, are not registered. It is known that absolute humidity highly affects the
charged fraction of the radon progeny; therefore, a humidity effect on the radon counting efficiency
of such instruments is reasonably expected. Simultaneous tests for all four instruments were
performed in the Radon Calibration Facility of our Laboratory (8.5 m3 air tight chamber) within a
relative humidity (φ ) range between 30 to 90% at 20-25 ° C, with radon concentrations between 0.35
to 4.53 kBqm-3 . No significant differences between the indications of the humidity sensors of the
Facility (external) and the radon instruments (internal) were observed. However, the internal
sensors registered temperatures about 2-4 °C higher than the external. The absolute humidity (ω ) is
evaluated by assuming steam as an ideal gas by the formula : ω = φ (18 pg)/(29pair),
where φ is the relative humidity, pg the saturation pressure of the steam at the prevailing
temperature and pair the ambient pressure. It is apparent that the absolute humidity has to be calculated
using environmental values indicated by the instruments internal sensors when available.
Figure 1 presents the humidity effect on the radon counting efficiency for one of the instruments
tested. Such graphs were also plotted for each of the other three instruments. It is concluded that
there seems to exist a linear correlation between absolute humidity and radon counting efficiency
with a 0.7 correlation coefficient in the range experimented. However, it is believed that for an
absolute humidity range wider than the one examined, the radon counting efficiency is dependent
rather on the square of the absolute humidity.
Instrument
CF = A0 + A1 ω2
Correlation
coefficient Residual
mean square
(%)
A0
A1
INSTR-1 2.40 0.69 0.65 18
INSTR-2 1.62 0.63 0.71 20
INSTR-3 1.45 -0.29 0.66 24
INSTR-4 0.72 0.20 0.66 17
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Radon in the Living Environment,
Athens, 1923 April 1999
BUILDING MATERIALS PHOTON ATTENUATION, NATURAL RADIOACTIVITY
CONTENT AND RADON EXHALATION RATE
N.P.Petropoulos, M.J. Anagnostakis and S.E. Simopoulos
Nuclear Engineering Section, Mechanical Engineering Dept.
National Technical University of Athens, 15780, Greece
High concentrations of natural radionuclides in building materials result in high dose rate indoors
due to radon and thoron exhalation and the γ-rays emitted from them. Among the natural
radionuclides contained in building materials, most attention has been given to 226Ra due to 222Rn
exhalation and the subsequent internal exposure. In external dose calculations due to building
materials it is usually assumed that there exists radioactive equilibrium among the radionuclides of
both the uranium and thorium series. In the case of the radionuclides of the uranium series it is
assumed that there exists radioactive equilibrium among the long lived radionuclides 238U, 226Ra
and 210Pb. The above assumption is seldom checked mainly because of the difficulties in the γ-spectroscopic
determination of 238U and 210Pb which is possible only by using low-energy
photons, where intense self-absorption of the photons inside the sample exists. In this case the
count-rate during a γ-spectroscopic analysis is highly affected by the intense self-absorption of the
photons. For the determination of radionuclides emitting low-energy photons a method has been
developed which needs as input among others the linear attenuation coefficient μ for the analysed
material. This paper presents:
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Radon in the Living Environment,
Athens, 1923 April 1999
BUILDING MATERIALS RADON EXHALATION RATE:
ERRICCA INTERCOMPARISON EXERCISE RESULTS
N.P. Petropoulos, M.J. Anagnostakis, and S.E. Simopoulos
Nuclear Engineering Section, Mechanical Engineering Dept.
National Technical University of Athens, 15780 Athens, Greece
The Nuclear Engineering Section of the National Technical University of Athens undertook the
organisation of a European building material radon exhalation rate intercomparison exercise in the
framework of the European Research into Radon In Construction Concerted Action (ERRICCA).
The intercomparison started in June 1998 and it was concluded in February 1999. Twenty
participants from 13 countries took part. The exercise focused on the radon exhalation rate
determination from a concrete slab, specially constructed to produce radon surface flux well below
10 mBqm-2s-1 . This paper describes the measurement results obtained using different instruments
and methods in order to assess the "state-of-the-art" of low-level radon exhalation measurements,
being performed around Europe. Results are compared to each other and they provide an
indication of the collective precision of such measurements for low exhalation rates. The
agreement, with a few exceptions, is satisfactorily good.
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The Science of the Total Environment, Vol. 272, pp. 261-272, 2001
RADIOENVIRONMENTAL SURVEY OF THE MEGALOPOLIS LIGNITE FIELD BASIN
P.K. Rouni, N.P. Petropoulos, M.J. Anagnostakis, E.P. Hinis and S.E. Simopoulos
Nuclear Engineering Section, Mechanical Engineering Dept.,
National Technical University of Athens, 15780 Athens, Greece
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Third International Symposium on Naturally Occuring Radioactive Materials
Brussels 17-21 September 2001
TECHNOLOGICALLY ENHANCED NATURAL RADIOACTIVITY OF FLY-ASH PRODUCED IN LIGNITE-FIRED POWER PLANTS AND THE ASSOCIATED RADIOLOGICAL IMPACT
D.J. Karangelos, P.K.Rouni, N.P.Petropoulos, M.J. Anagnostakis, E.P.Hinis and S.E. Simopoulos
Nuclear Engineering Section, Mechanical Engineering Dept.,
National Technical University of Athens, 15780 Athens, Greece
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Archive of Oncology 2001;9(4):231-6
DETERMINATION OF DEPLETED URANIUM IN ENVIRONMENTAL SAMPLES BY GAMMA-SPECTROSCOPIC TECHNIQUES
M.J. Anagnostakis, E.P. Hinis, D.J. Karangelos, N.P. Petropoulos, P.K. Rouni, S.E. Simopoulos
Nuclear Engineering Section, Mechanical Engineering Dept.,
National Technical University of Athens, 15780 Athens, Greece
Z.S. Zunic
Radiation Medicine Department, Institute of Nuclear Sciences "VINCA", Belgrade, Yugoslavia
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Kerntechnik 68 (2001) 1-2
EXPERIMENTAL INVESTIGATION OF THE REWETTING PROCESS AT PRESSURES OF 1-7 BAR
E.P. Hinis and S.E. Simopoulos
Nuclear Engineering Section, Mechanical Engineering Dept.,
National Technical University of Athens, 15780 Athens, Greece
Several water experiments have been carried out to investigate the physical mechanisms relevant to the rewetting phenomena either at atmospheric conditions or in a steam environment. Yet, there seems to be a scarcity of experimental data for the low pressure range from 2 to 7 bar with parameters the liquid film flowrate and the subcooling. An experimental facility to simulate two-phase low-pressure water flow phenomena has been designed, constructed and employed to investigate the rewetting process of hot surfaces in a water-steam environment at pressures in the above range, as well as at atmospheric conditions; the facility is on-line interfaced to computers which control its operation and undertake all the data acquisition tasks. Furthermore, a numerical method to experimentally evaluate the wet front position along the rod was introduced. The present paper describes the experimental work aimed at studying the wet front propagation along a stainless steel fuel rod, in a top-flooding environment in the pressure range 1-7 bar, wall temperatures up to 550°C and at a liquid flowrate of 10-3m3min-1 at both saturated steam conditions and in atmospheric environment with water subcooling in the range 0-75K. The experimental results fitted well to an existing dimensionless rewetting correlation, together with world available vapour environment rewetting data extending its validity down to the pressure of 1 bar. Furthermore, the effect of the inlet water subcooling was introduced in to this correlation.
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CCMS Workshop: "Risk Assesment of Chernobyl Accident Consequences"
Kiev, 9-12 April 2002
GEOGRAPHICAL MAPPING AND ASSOCIATED FRACTAL ANALYSIS OF THE LONG-LIVED CHERNOBYL FALLOUT RADIONUCLIDES IN GREECE
N.P.Petropoulos, M.J. Anagnostakis, E.P. Hinis and S.E. Simopoulos
Nuclear Engineering Section, Mechanical Engineering Dept.,
National Technical University of Athens, 15780 Athens, Greece
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NRE VII, International Symposium
May 20-24, 2002, Rhodes, Greece
RADIOENVIRONMENTAL SURVEY OF THE MEGALOPOLIS POWER PLANTS FLY-ASH DEPOSITS
D.J. Karangelos, P.K. Rouni, N.P. Petropoulos, M.J. Anagnostakis, E.P. Hinis and S.E. Simopoulos
Nuclear Engineering Section, Mechanical Engineering Dept.,
National Technical University of Athens, 15780 Athens, Greece
NRE VII, International Symposium
May 20-24, 2002, Rhodes, Greece
DISTURBANCE OF RADIOACTIVE EQUILIBRIUM IN THE ASHES PRODUCED IN LIGNITE FIRED POWER PLANTS
D.J. Karangelos, N.P. Petropoulos, M.J. Anagnostakis, E.P. Hinis and S.E. Simopoulos
Nuclear Engineering Section, Mechanical Engineering Dept.,
National Technical University of Athens, 15780 Athens, Greece
Coal- and lignite-fired power plants
produce significant amounts of ashes, which are quite often being used as
additives in cement and other building materials. In many cases, coal and
lignite present high concentrations of naturally occurring radionuclides, such
as 238U, 226Ra, 210Pb, 232Th and 40K.
Moreover, during the combustion process the produced ashes are enriched in the
above radionuclides, thus characterized as Technologically
Enhanced Naturally Occurring Radioactive Materials (TENORM). The most
important naturally occurring radionuclide in such power plant ashes is 226Ra,
since it produces radon, which when exhaled contributes significantly to the
dose received by workers and the public. An extensive research project for the
determination of the natural radioactivity of lignite and ashes from Greek
lignite-fired power plants is in progress in the Nuclear Engineering Section of
the National Technical University of Athens (NES-NTUA) since 1983. From the
results obtained so far, it may be concluded that 226Ra
radioactivity of fly-ash in some cases exceeds 1kBqkg-1, which is
very high compared to the mean 226Ra radioactivity of surface soils
in Greece (25Bqkg-1). Furthermore, the radioactivity of 210Pb
in fly-ash may reach the value of up to 4kBqkg‑1, depending on
the sampling location inside the power plant. This paper
presents: natural
radioactivity results from the analysis of the lignite fed to and the ashes
produced in Greek lignite-fired power plants, and enrichment ratios of natural radionuclides
in the ashes collected at different stages along the emission control system of
the power plant. Enrichment ratio results are being interpreted in relation to
the physical properties of the investigated nuclides and the temperature in the
flue gas pathway. The different enrichment of the various nuclides of uranium
series along emission control system, results to a disturbance of their
radioactive equilibrium, which is more pronounced towards the end of the flue
gas pathway. Furthermore, the fly-ash collected in several points along the
emission control system of the power plant was investigated, in terms of radon
exhalation rate.
NRE VII, International Symposium
May 20-24, 2002, Rhodes, Greece
URANIUM-238 AND ITS DAUGHTER PRODUCTS IN GREEK SURFACE SOILS
M.J. Anagnostakis, E.P. Hinis and S.E. Simopoulos
Nuclear Engineering Section, Mechanical Engineering Dept.,
National Technical University of Athens, 15780 Athens, Greece
High concentrations of natural radionuclides in the soil can result in high dose rates outdoors mainly due to external exposure.
In dose calculations, the main radionuclides of interest are 226Ra, 232Th and 40K. Research till recent years has focused mainly
into the evaluation of 226Ra concentration, due to radon exhalation from the ground, and due to its relatively simple determination through its gamma
emitting decay products. Other radionuclides of the uranium series such as 238U and 210Pb, emitting low energy photons are not usually determined
due to γ-spectroscopic difficulties, and for dosimetric calculations an assumption of radioactive equilibrium among the nuclides of the uranium (238U)
series as well as the nuclides of the thorium (232Th) series is usually adopted. Among the nuclides of the uranium series, radioactive disequilibrium
may exist, and this is the case of the relatively long-lived nuclides 238U (T½ = 4.47 109y), 226Ra (T½ = 1600y) and 210Pb (T½ = 22.2y) for several
reasons, such as leaching, rock weathering, radon exhalation from the ground etc. Radioactive equilibrium may also be disturbed because of human
activities, such as the existence of coal fired power plants and the resulting fly-ash fallout.
An extensive research has been undertaken by the Nuclear Engineering Laboratory of the National Technical University of Athens (NES-NTUA) for the
investigation of the natural and artificial radioactivity in greek surface soils. This research has resulted to the mapping of 226Ra, 232Th and 40K in greek
surface soils, as well as the mapping of radionuclides of the Chernobyl fallout in Greece. The gamma spectroscopic determination of 238U and 210Pb,
which emit low energy photons of 63.29keV and 46.5keV respectively, with very low yields, requires the use of detectors with high efficiency in the low
region below 200keV, such as LEGe or XtRa detectors, and special techniques for self-absorption corrections inside the samples.
Due to the time consuming and difficult determination of the low activities of 238U and 210Pb in environmental samples such as soil, only recently such
results are found in the literature. In the framework of this research soil samples from allover Greece are analysed for 238U, 226Ra and 210Pb.
From the samples analysed so far, the conclusion may be drawn that, when 226Ra concentration is much lower than about 25Bqkg-1, which is
incidentally the mean value for 226Ra of greek surface soils, radioactive equilibrium is significantly disturbed, and the ratio 226Ra/238U may
be as low as 0.3. In the case where 226Ra activity is much higher than 25Bqkg-1, radioactive equilibrium is again significantly disturbed with the ratio
226Ra/238U reaching values as much as 4. The above findings indicate that extreme values of 226Ra in surface soils may be the result of 226Ra
leaching. This research is currently focused on the mapping of uranium at surface soils in specific locations in Greece, and on the investigation of its
association with that of 226Ra. Concerning the concentration of 210Pb in surface soils, the analyses performed show that is was almost always
higher than that of 226Ra, probably due to radon exhalation from the ground. Analyses of soil samples from deeper soil layers are also performed,
in order to investigate the vertical profile of the radionuclides under study.
NRE VII, International Symposium
May 20-24, 2002, Rhodes, Greece
SURVEY OF DEPLETED URANIUM CONTAMINATION IN SOIL AND VEGETATION USING γ-SPECTROSCOPY
Z.S. Zunic
Radiation Medicine Department, Institute of Nuclear Sciences "Vinca",
PO Box 522, 11001 Belgrade, Yugoslavia
D.J. Karangelos, M.J. Anagnostakis, E.P. Hinis and S.E. Simopoulos
Nuclear Engineering Section, Mechanical Engineering Dept.
National Technical University of Athens, 15780 Athens, Greece
The use of depleted uranium (DU) in military operations results to contamination of the target area due to DU dispersion in the environment. Since uranium isotopes are naturally occurring
radionuclides, DU is characterized as Technologically Enhanced Naturally Occurring Radioactive Material (TENORM). The determination of DU contamination in environmental samples
is a difficult task because the isotopes of uranium 238U and 235U that exist in DU also exist in natural uranium, which is detected in almost
all environmental samples as trace element. Since the isotopic abundance in DU is different from that in nature, the only evidence that environmental samples are contaminated
by DU is the disruption of the natural isotopic abundance of 235U and 238U in the analysed sample. For the investigation of the existence of such
disruption, the accurate quantitative determination of 235U and 238U is necessary. Because of the extremely long half-lives of the uranium isotopes and
the low energy photons that they emit, their determination by gamma-spectroscopy requires the use of special detectors and techniques.
The Nuclear Engineering Section of the National Technical University of Athens (NES-NTUA) uses high-resolution LEGe detectors and especially developed gamma spectroscopic analysis
techniques for the determination of 235U and 238U and subsequently for the isotopic abundance of the uranium isotopes in the sample.
The analysis of the multiplet photopeak at 186keV with the LEGe detector, leads -through its two components- to the determination of 235U. Since 235U and
238U already exist in the natural sample prior to contamination, DU may be detected with this technique if 238U in the DU is higher than the 1/5 of the 238U in the
natural uranium in the sample. This technique is relatively easy to apply, compared to those that involve radiochemical analysis and it may be used for screening purposes and
for mapping in DU target areas. From the analysis of surface soil samples from allover Greece and from areas of Kosovo, collected well before the dispersion of depleted uranium in the area,
which have been performed in NES-NTUA it has become evident that the Kosovo area is a natural high background area with a pronounced surface soil variation in natural uranium content,
and 238U activity reaching values as high as 360Bqkg-1. It was also observed that disturbance of radioactive equilibrium among the nuclides of the uranium
series is quite often observed due to leaching and weathering, with the ratio of the activities of 238U and 226Ra ranging from 0.17 to 3.4.
After the military operations in Kosovo, environmental samples from a DU target area were collected and analysed in NES-NTUA. The surface soil samples were collected in and around
a DU penetrator crater, in a systematic way, to allow for DU contamination mapping. Samples were also collected and analysed from deeper soil layer to allow the investigation
of DU vertical migration and from vegetation. Preliminary results from the analyses performed so far show that a few of the analysed soil samples were found contaminated by DU,
with 238U activity exceeding by far 1kBq, and ratio of 238U/226Ra exceeding the value of 10. In these contaminated soil samples,
the natural isotopic abundance of the uranium isotopes was significantly disrupted, and allowed for an estimation of the isotopic abundance of 235U about 0.2% which
agrees very well with relevant values found in the literature for DU penetrators. Vegetation samples imported from Yugoslavia as well as other Balcan countries to
Greece, were also analysed by gamma spectroscopy, but their content in DU was below the detection limit of 1Bqkg-1 for 238U.
NRE VII, International Symposium
May 20-24, 2002, Rhodes, Greece
DATA LEADING TO THE INVESTIGATION OF A RELATION BETWEEN SEISMIC ACTIVITY AND RADON DAUGHTERS CONCENTRATION OUTDOORS
D.J. Karangelos, N. P. Petropoulos, M.J. Anagnostakis, E.P. Hinis and S.E. Simopoulos
Nuclear Engineering Section, Mechanical Engineering Dept.,
National Technical University of Athens, 15780 Athens, Greece
The continuous monitoring of radon daughters concentration outdoors has been a part of the Athens area environmental radioactivity monitoring program of the Nuclear Engineering
Section of the National Technical University of Athens (NES-NTUA) since the mid '80s. The monitoring system consists of a Sodium-Iodide (NaI) detector and appropriate electronics
including a spectrum stabilizer suitable to compensate for spectrum shifts mainly due to large temperature variations. The radon daughter photons to be monitored are mainly those
of 214Pb (352 keV) and 214Bi (609 keV). Both single channel analysis in regular time intervals and a spectrum collection over 24 hr intervals through a multi
channel analyzer are employed. Data acquisition is computer driven and fully automated. Through this 15-year long operation of the system, observations were made that the radon daughters
concentration outdoors was significantly increased for a time window of 5 to 8 days before a seismic event, probably due to precursory earth cracks. Furthermore, it has been
heuristically concluded that (a) a radon daughters concentration increase has been detected before all earthquakes of magnitude >4.5R within a radius of 200 km from Athens (b) a radon
daughters concentration increase has been detected before all earthquakes of magnitude >3.5R within a radius of 50 km from Athens and (c) no false positive increases have been
detected so far. These heuristic conclusions suggested that an increase of radon daughters concentration outdoors might be an earthquake precursor for the area under study.
Following this suggestion data collection was enhanced to record rainfall and total γ-background; both these parameters might indicate a probable false positive signal which has to
be filtered out. Furthermore, adaptive control of sampling intervals was introduced so that every case of significant radon daughters concentration increase is represented with adequate
statistics. This paper presents a first attempt for the analysis of such data. Data treatment involved mathematical methods for (a) subtracting the total γ-background from the signal (b)
eliminating the rainfall effect on the signal and (c) discriminating the signal from noise. It was then attempted to correlate signal data with earthquake data such as magnitude and
Athens to epicenter distance. The analysis results obtained indicate that this monitoring method gives a reliable indication for an earthquake within a reasonable time window.
In addition, after establishing a proper monitoring network, the epicenter may be located with acceptable accuracy. A correlation between radon daughters concentration increases
and earthquake magnitudes may be established after a network monitoring for a long time, despite the fact that experimental conditions towards this end are unpredictable and unfavorable.
This precursory method may prove useful if combined with other similar tools. Research is under way to investigate whether excess radon daughters concentration is air transported from
the epicenter site or it is due to increased soil radon exhalation at the monitoring station .
NRE VII, International Symposium
May 20-24, 2002, Rhodes, Greece
REDUCING THE NATURAL RADIOACTIVITY BACKGROUND IN Ge DETECTOR SHIELDS
A.Nikoglou, D.J. Karangelos, P.K.Rouni, M.J. Anagnostakis, E.P. Hinis and S.E. Simopoulos
Nuclear Engineering Section, Mechanical Engineering Dept.,
National Technical University of Athens, 15780 Athens, Greece
Gamma spectroscopy is a widely used technique for the qualitative and quantitative determination of gamma emitting radionuclides in a variety of samples.
There are cases where the total activity of the radionuclides of interest in the analysed samples is extremely low. Typical such radionuclides are those of natural radioactivity in water samples,
foodstuff, or even air-filters through which large volumes of air have been pumped for the determination of the radionuclides content in the air. Though Ge detectors used for such
measurements of natural radionuclides are almost always equipped with very efficient detector shields, the existence of background radiation, due to the photons emitted from the
environment outside the shield, the shield itself and the detector cryostat cannot be totally avoided or neglected. This background poses limitations to the lower limit of detection and the
accuracy of the measurements performed, and should be minimized as possible. One important background contributor is the radon decay products, in and around the detector chamber,
which is described as the interior of the detector shield. Among the radon daughters, the most important background contributors are 214Pb and 214Bi,
which emit a total of five important photons with energies 295.22keV, 351.99keV, 609.32keV, 1120.28keV and 1764.51keV, which are often used for the 226Ra indirect
determination. Besides the background fluctuations due to pure statistics, radon daughters concentration imply an additional background fluctuation.
Gamma spectroscopy measurements in the Nuclear Engineering Section of the National Technical University of Athens (NES-NTUA) are performed in the gamma spectroscopy laboratory,
which is equipped with a wide variety of Ge detectors, the oldest being a 20 years old GeLi detector with 24% efficiency and the newest an XtRa detector with 107% efficiency.
The laboratory has recently moved to the basement of a new building. From repeated and extensive background measurements in the new building, it was concluded that the
detectors background was increased probably due to the building aging; furthermore unreasonable background fluctuations were experienced. Because of its high efficiency, the
XtRa detector was subject to the most pronounced background changes. For this reason, a detailed investigation of the factors affecting the radon concentration inside the room
and the detectors background was undertaken. The radon activity inside the room was monitored as a function of parameters such as ventilation and air conditioning inside the room,
and it was found to vary from 40 Bqm-3 to as much as ~120Bqm-3, over a two years period. The best conditions for as low as possible radon
concentration indoors were: no air-conditioning inside the room, natural ventilation through the open doors and the increase of the air circulation by using a shaft especially constructed
for this purpose. Furthermore, an effort was undertaken to reduce the background due to the radon daughters inside the detectors chambers, using various techniques. Among them the most
effective it proved to be:
The latter was accomplished with fitting inside the chamber a light aluminium construction, made from a very thin aluminium foil of high purity, which was filled with nitrogen.
This construction almost completely fills the XtRa detector chamber, leaving space only for the samples to be analysed, thus significantly reducing radon environment inside the chamber.
From the results obtained so far, it was concluded that this was the most efficient way to reduce the background, with a reduction factor of about 0.7, and almost vanishing the background
fluctuations.
NRE VII, International Symposium
May 20-24, 2002, Rhodes, Greece
ASSOCIATION OF THE CHERNOBYL FALLOUT ISOTOPES PATTERNS WITH THOSE OF RAINFALL IN GREECE
M. Michelaraki
Department of Climatology,
Hellenic National Meteorological Service166 03 Athens, Greece
P.F. Vrantzas, N.P.Petropoulos, E.P. Hinis and S.E. Simopoulos
Nuclear Engineering Section, Mechanical Engineering Dept.,
National Technical University of Athens, 15780 Athens, Greece
A wide soil-sampling programme was undertaken right after the Chernobyl accident in Greece by the Nuclear Engineering Section of the National Technical University of Athens (NES-NTUA),
in order to detect and quantitatively analyse the long-lived radionuclides in the Chernobyl fallout. Samples (1242) of 1cm thick surface soil were collected[1] all over Greece
during the period from May to November 1986. The samples were counted and analysed using Ge detector set-ups. An in-house unix-based data base/geographical information
system was developed for the detailed mapping of the ten radionuclides 137Cs, 134Cs, 144Ce, 141Ce 125Sb, 106Ru, 103Ru, 95Zr, 110mAg and 54Mn mainly deposited in Greece.
Multi-fractal analysis has also been performed. This analysis has already been published ([2],[3]) and showed that there exist differences in the spatial distribution of the above
radionuclides. These differences are primarily attributed to different deposition pathways and mechanisms and different arrival dates. In the present work, a statistical technique
to compare contour maps is introduced and applied to explain the differences,in the fallout patterns of the above-mentioned radionuclides.
As a result of this analysis, it was made clear that there are two main subsets of radionuclides (a): 137Cs, 134Cs, 144Ce,
141Ce 125Sb, 106Ru, 103Ru and 95Zr, and (b):110mAg and 54Mn, deposited in distinct ways.
Furthermore, the weekly rainfall during the period from April 26th to May 30th was mapped. Multifractal analysis of the rainfall patterns has also been performed.
The above two radionuclide subsets, were compared with the rainfall patterns using an introduced statistical technique.
As a result, the pattern overlapping ratio was calculated and it was concluded that the 137Cs subset was deposited during the week May 3rd - 9th, 1986,
while the 110mAg subset was deposited during the following week May 10th -16th, 1986.
References
NRE VII, International Symposium
May 20-24, 2002, Rhodes, Greece
RADON-IN-WATER SECONDARY STANDARD PREPARATION
D.J. Karangelos, N. P. Petropoulos, E.P. Hinis and S.E. Simopoulos
Nuclear Engineering Section, Mechanical Engineering Dept.,
National Technical University of Athens, 15780 Athens, Greece
Radon-in-water standard solutions are required for the calibration and quality control of instruments measuring Radon concentration in water samples.
However, due to the short half-life of Radon, such standards are not widely available.This work presents a method developed at the NES-NTUA to generate Radon-in-water solutions
of known concentration that can easily be applied in a laboratory with access to a Radon-in-air calibration facility. Air with the appropriate concentration of Radon is bubbled
through deionized distilled water, giving a solution with the desired Radon concentration, as predicted by published Radon solubility data. Operating parameters have been suitably
chosen so that volumes in the order of liters can be generated, with concentrations from less than 1 Bq/lt up to some tens of Bq/liter, depending on the Radon source used.
The entire process takes less than 30 minutes, excluding the time for the original build-up of Radon in the reference Radon chamber.A series of experiments conducted to
validate the method is presented, where the samples produced were measured using active instrumentation coupled to a Radon bubbler.
The concentrations tested ranged from 3 to 17 Bq/lt. Performance in terms of precision and accuracy was found to be adequate. An example is also given, with this method
applied to check the calibration of a Radon-in-water measuring apparatus based on a gas-transfer membrane.The method has been proven to be accurate enough for the
solution produced to be usable as a secondary standard, traceable to within 10% of the calibration of the original Radon source.
This fact, as well as other attractive features such as low running cost and ease of use, makes it appropriate for purposes such as quality control, intercalibration of instruments
and laboratory intercomparison.
Industry Technology Environment International Conference
Moscow, 18-20 September 2002
TECHNOLOGICALLY ENHANCED NATURAL RADIOACTIVITY OF FLY-ASH PRODUCED IN COAL BURNING POWER PLANTS AND THE ASSOCIATED RADIOLOGICAL IMPACT
D.J. Karangelos, P.K.Rouni, N.P.Petropoulos, M.J. Anagnostakis, E.P.Hinis and S.E. Simopoulos
Nuclear Engineering Section, Mechanical Engineering Dept.,
National Technical University of Athens, 15780 Athens, Greece
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First Workshop on Natural Radionuclides in Hydrology and Hydrogeology
Luxembourg, 4-7 September 2002
RADON-IN-WATER SECONDARY STANDARD PREPARATION IN A WIDE ACTIVITY CONCENTRATION RANGE
D.J. Karangelos, N.P. Petropoulos, E.P. Hinis and S.E. Simopoulos
Nuclear Engineering Section, Mechanical Engineering Dept.,
National Technical University of Athens, 15780 Athens, Greece
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Journal of Environmental Radioactivity 61:257-269, 2002
PHOTON ATTENUATION, NATURAL RADIOACTIVITY CONTENT AND RADON EXHALATION RATE OF BUILDING MATERIALS
N.P. Petropoulos, M.J. Anagnostakis and S.E. Simopoulos
Nuclear Engineering Section, Mechanical Engineering Dept.,
National Technical University of Athens, 15780 Athens, Greece
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