Collective Dose Commitment Research Articles

Temporal Trend in the Transfer of Sellafield-Derived 14C into Different Size Fractions of the Carbonate Component of NE Irish Sea Sediment

From 1994 onwards, radiocarbon discharges from the Sellafield nuclear fuel reprocessing plant have been made largely to the northeast Irish Sea. They represent the largest contributor to UK and European populations of the collective dose commitment derived from the entire nuclear industry discharges. Consequently, it is important to understand the long-term fate of 14C in the marine environment. Research undertaken in 2000 suggested that the carbonate component of northeast Irish Sea sediments would increase in 14C activity as mollusk shells, which have become enriched in Sellafield-derived 14C, are broken down by physical processes including wave action and incorporated into intertidal and subtidal sediments. The current study, undertaken in 2011, tested this hypothesis. The results demonstrate significant increases in 14C enrichments found in whole mussel shells compared to those measured in 2000. Additionally, in 2000, there was an enrichment above ambient background within only the largest size fraction (>500 μm) of the intertidal inorganic sediment at Nethertown and Flimby (north of Sellafield). In comparison, the present study has demonstrated 14C enrichments above ambient background in most size fractions at sites up to 40 km north of Sellafield, confirming the hypothesis set out more than a decade ago.

Investigations on the activity concentrations of 238U, 226RA, 228RA, 210PB and 40K in Jordan phosphogypsum and fertilizers

The activity concentrations of naturally occurring radionuclides ((238)U, (226)Ra, (228)Ra, (210)Pb and (40)K) in Jordanian phosphate ore, fertilizer material and phosphogypsum piles were investigated. The results show the partitioning of radionuclides in fertilizer products and phosphogypsum piles. The outcome of this study will enrich the Jordanian radiological map database, and will be useful for an estimation of the radiological impact of this industrial complex on the immediate environment. The activity concentration of (210)Pb was found to vary from 95 +/- 8 to 129 +/- 8 Bq kg(-1) with a mean value of 111 +/- 14 Bq kg(-1) in fertilizer samples, and from 364 +/- 8 to 428 +/- 10 Bq kg(-1) with a mean value of 391 +/- 30 Bq kg(-1) in phosphogypsum samples; while in phosphate wet rock samples, it was found to vary between 621 +/- 9 and 637 +/- 10 Bq kg(-1), with a mean value of 628 +/- 7 Bq kg(-1). The activity concentration of (226)Ra in fertilizer samples (between 31 +/- 4 and 42 +/- 5 Bq kg(-1) with a mean value of 37 +/- 6 Bq kg(-1)) was found to be much smaller than the activity concentration of (226)Ra in phosphogypsum samples (between 302 +/- 8 and 442 +/- 8 Bq kg(-1) with a mean value of 376 +/- 62 Bq kg(-1)). In contrast, the activity concentration of (238)U in fertilizer samples (between 1011 +/- 13 and 1061 +/- 14 Bq kg(-1) with a mean value of 1033 +/- 22 Bq kg(-1)) was found to be much higher than the activity concentration of (238)U in phosphogypsum samples (between 14 +/- 5 and 37 +/- 7 Bq kg(-1) with a mean value of 22 +/- 11 Bq kg(-1)). This indicates that (210)Pb and (226)Ra show similar behaviour, and are concentrated in phosphogypsum piles. In addition, both isotopes enhanced the activity concentration in phosphogypsum piles, while (238)U enhanced the activity concentration in the fertilizer. Due to the radioactivity released from the phosphate rock processing plants into the environment, the highest collective dose commitment for the lungs was found to be 1.02 person nGy t(-1). Lung tissue also shows the highest effect due the presence of (226)Ra in the radioactive cloud (0.087 person nGy t(-1)).

Estimate of the dose-increment due to outdoor exposure to gamma rays from uranium progeny deposited on the soil around a coal-fired power plant in Ajka Town, Hungary.

Brown coal unusually rich in uranium is burnt in a coal-fired power plant that lies inside the confines of a small industrial town named Ajka, Hungary, and has been operational since 1943. The 238U (226Ra) activity discharged to the atmosphere per unit electrical energy produced was about 330-400 GBq (GW y)(-1), which is 66-80 times more than that was estimated by UNSCEAR (1988) as a characteristic value for old type coal-fired power plants [5 GBq (GW y)(-1)]. The objective of this study was the experimentally established assessment of the artificial increment in the dose from external exposure to gamma rays of terrestrial radionuclides outdoors. Soil samples were collected in and near Ajka from 81 locations. The samples were investigated by Ge(Li) gamma spectrometry. Considerably elevated concentrations of uranium and its progeny have been measured in most of the samples that were collected near to the plant. Concentrations of 238U and 226Ra in the top (0-5 cm depth) layer of undisturbed soil at public areas inside town were 4.7 times higher, on average, than those in the uncontaminated deeper layers. Dose rate in air (air kerma) from external exposure to terrestrial gamma rays outdoors at a height of 1 m and effective doses were estimated from the measured activity concentrations using some relevant literature data. The estimated artificial increment in the dose rate in air was, on average, 32.8, 10.3, and 102.1 nGy h(-1) at public areas, vegetable gardens, and backyards, respectively. The mean artificial increment in the annual per caput effective dose from external exposure to terrestrial radionuclides outdoors is 21.8 microSv y(-1). The collective dose commitment per unit energy generated from outdoor exposure to the deposited uranium progeny is about 8.0-9.1 person Sv (GW y)(-1), which is 67-76 times more than that evaluated by UNSCEAR (1988) for a typical "old" coal-fired power plant [0.12 person Sv (GW y)(-1)]. Ajka is a suitable place for studying the dosimetric consequences of the utilization of coal for energy production experimentally.

Estimates of Collective Doses from a Hypothetical Accident of a Nuclear Submarine

The collective dose to the Japanese population has been estimated from a hypothetical accident of a nuclear submarine if it sinks in an offshore region around Japan. A computer code system DSOCEAN has been used for assessing the collective dose due to radionuclides released to the ocean from a sunken nuclear submarine. The estimated collective effective dose commitment from all of the radionuclides released after the break of the fuel pellets is estimated to be 2.5 x104 man-Sv. The contribution of 241Am to the total collective effective dose commitment is the highest, followed by 137Cs, 238Pu, 240Pu, 239Pu and 241 Pu. The maximum of the estimated collective effective dose by the annual intake of marine products after radionuclide releases for one year is approximately 0.3% of the annual average dose by the natural radiation that is reported by UNSCEAR.

Radiological impact from atmospheric releases of 238U and 226Ra from phosphate rock processing plants

Phosphate rocks are used extensively, mainly as a source of phosphorus for fertilizers and secondarily for phosphoric acid and other speciality chemicals. Phosphates are typically enriched in uranium and are thus one of the sources of technologically enhanced natural radiation (TENR) which increases exposure to man from natural radionuclides. Emissions from phosphate rock processing plants in gaseous and particulate form contain radionuclides, such as 238U and 226Ra, which are discharged into the environment causing radiation exposures to the population. About 10 MBq each of 238U and 226Ra are discharged into the environment each year from SICNG, a phosphate rock processing plant in Thessaloniki area, Northern Greece. The collective dose commitment to lung tissue resulting from atmospheric releases was estimated to be ∼2×10 −9 person Gy t −1 for 238U and ∼0.1×10 −9 person Gy t −1 for 226Ra, i.e. about 2 times higher than that estimated in the UNSCEAR reports issued in 1982, 1988, and 1993.

Radiological Impact on EC Member States of Routine Discharges into the Mediterranean Sea

The radiological impact of liquid discharges released into the Mediterranean Sea from European civil nuclear plants in the period 1980-1991 has been assessed. This assessment was part of the achievement of a group of experts set up in 1992 by the Commission of the European Communities to examine the overall radiological impact on the European population from natural and man-made nuclides in the Mediterranean Sea (Project MARINA-MED). A mathematical model, ATOMED, was used to predict the dispersion of radionuclides in the Mediterranean Sea, the transfers to the biota and sediments, and to assess the radiological exposure of the population of the European Community. Annual liquid discharges from each site and seafood catch statistics were provided by experts involved in the MARINA-MED project. The total collective dose commitment truncated at 500 years delivered to the EC population following the discharge of liquid radioactive effluents in the period 1980-1991 has been calculated to be 1.96 man Sv.

Effective dose estimation for the population in Kragujevac due to the Chernobyl accident

The doses that inhabitants of Kragujevac received after the nuclear accident in Chernobyl are given in this paper. During April and May in 1986, the radionuclide content in rain water was determined by applying gamma spectroscopic analysis, and the exposure dose rate in air was measured. The results obtained are the basis for absorbed dose, effective dose and commitment dose calculations. The effective dose, that some individuals received for the first year after the accident, due to the external exposure was estimated to be 50 μSv. Thus, the collective effective dose commitment due to the external exposure for population in Kragujevac town amounts to 11.5 Sv man. The effective dose from internal radiation due to 131I and 137Cs was also estimated, and amounted to 195 μSv in the first year. The collective effective dose commitment, due to the internal exposure (for 50 years) will be 43 Sv man. The total effective dose commitment (50 years) will be 0.32 mSv, while the total collective effective dose commitment will be 54.5 Sv man.

A comparison of doses from 137Cs and 210Po in marine food: A major international study

Radioactivity levels of natural 210Po and anthropogenic 137Cs in sea water and biota (fish and shellfish) have been estimated for the FAO fishing areas on the basis of measurements carried out in recent years. Collective doses resulting from seafood consumption are calculated for each FAO area using radioactivity data for water and biota. Good agreement is observed between the results calculated by these two methods, with the exception of the doses from 210Po via shellfish consumption. The collective effective dose commitment from 137Cs in marine food in 1990 has been estimated at 160 man Sv with an uncertainty of 50%. The corresponding dose from 210Po is 30000 man Sv with an estimated uncertainty of a factor of 5. The results confirm that the dominant contribution to doses derives from natural 210Po in fish and shellfish and that the contribution from anthropogenic 137Cs (mainly originating from nuclear weapons tests) is negligible.

The Behavior of Sellafield-Derived 14C in the Northeast Irish Sea

Radiocarbon is an important constituent of the low level, liquid, radioactive effluent discharged from the Sellafield nuclear fuel reprocessing plant in northwest England, but despite the fact that it gives the highest collective dose commitment of all the nuclides in the waste, its behavior in the Irish Sea is poorly defined. There is therefore a clear requirement for an improved understanding of 14C behavior in the Irish Sea, to assist with dose evaluation modeling and definition of the mixing and accumulation characteristics of the sediment in this area. In this context, results are presented here for a temporal study of 14C activities in four geochemical fractions of seawater and in a sediment core from the vicinity of the Sellafield effluent outfall. Clear 14C enrichments in the dissolved inorganic carbon (DIC) and particulate organic carbon (POC) components of seawater were observed, with temporal trends in activity that were related to variations in the Sellafield discharge. Smaller, but nevertheless detectable, enrichments were also observed for particulate inorganic carbon (PIC) and dissolved organic carbon (DOC) in the seawater. The distribution of 137Cs and 241Am revealed that the sediment core could be classified into three zones in which the intensity of mixing decreased discontinuously with depth. Bulk carbonate 14C analyses of the core demonstrated the presence of glacial or pre-glacial carbonate in the system, but failed to show any evidence of contaminant 14C input or provide information on sediment accumulation processes. In contrast, analysis of bulk organic matter from the sediment provided clear evidence of the recent perturbation of a well mixed system by input of younger material, consistent with the recent input of contaminant 14C from Sellafield and possibly weapons testing fallout.

137Cs Chernobyl fallout in Greece and its associated radiological impact

Right after the Chernobyl reactor accident, a systematic soil sampling and analysis programme was undertaken to detect and quantitatively analyse the long-lived radionuclides in the Chernobyl fallout in Greece. In the frame of this programme, 1242 soil samples of 1-cm 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 137Cs deposition in the form of a five-class histogram, extending between 0 – 150 kBq m −2, with boundaries defined by isolines of 5, 15, 35, 65, and 150 kBq m −2. To investigate the radiological impact of the 137Cs fallout on the Greek population, the 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 was estimated as 340 manSv over the first year after the accident and 8800 manSv over a period of 40 y. Concerning the 6000 inhabitants within the 65 kBqm −2 isoline, the results were 2 manSv over the first year after the accident and 55 manSv over a period of 40 y. The above radiological impact was compared to that due to fly ash releases from the Ptolemais Lignite Power Plants in northern Greece.

Experimental Study on the Removal of 14C in Radioactive Liquid Waste.

Carbon-14 gives the largest collective dose commitment to the world population among the nuclides which are discharged from nuclear fuel cycle facilities, therefore this is a very important nuclide from the viewpoint of radiation protection. In neutron fields as in the vicinity of the cores of nuclear reactors, there are several nuclear reactions which regularly generate 14C in operation. Carbon-14 generated in water is contained in radioactive liquid waste on the occasion of maintenance of reactors etc. Because 14C emits only weak β-rays, it is difficult to detect 14C in liquid waste by ordinary monitoring methods. Therefore 14C has not been recognized as a major object for the treatment of radioactive liquid waste, and there has been little information on the treatment of 14C in water.In this study, we performed experiments on the treatment of 14C in liquid waste by conventional treatment methods for radioactive liquid waste such as ion exchange, chemical coagulation and precipitation, and evaporation. We examined the validity of these methods and the behavior of 14C liquid in waste. The knowledge obtained in this study is important to develop effective removal methods for 14C in liquid waste.

Age-dependent variation of selenium-75 biokinetics in rat.

Substantial levels of selenium-79 (79Se) in radioactive waste from the nuclear fuel cycle, may result in a significant collective dose commitment following release into the environment. Few data are available from which the effective dose equivalent among subgroups of the general population can be made. Accordingly, whole body retention and organ content were studied in neonate, adult and pregnant rat following oral contamination with 75Se. The results for whole-body retention conformed to a two-component exponential with terminal biological half-time of about 40, 30 and 20 days in adult male, neonate and pregnant rat, respectively. The highest concentrations of Se occurred in the liver, kidney, and testis. Influence of Se kinetics as a function of age and physiological development on dose estimates are discussed. Results were consistent with current dosimetric models but suggested that the testis should also be included.

The global impact of the Chernobyl reactor accident.

Radioactive material was deposited throughout the Northern Hemisphere as a result of the accident at the Chernobyl Nuclear Power Station on 26 April 1986. On the basis of a large amount of environmental data and new integrated dose assessment and risk models, the collective dose commitment to the approximately 3 billion inhabitants is calculated to be 930,000 person-gray, with 97% in the western Soviet Union and Europe. The best estimates for the lifetime expectation of fatal radiogenic cancer would increase the risk from 0 to 0.02% in Europe and 0 to 0.003% in the Northern Hemisphere. By means of an integration of the environmental data, it is estimated that approximately 100 petabecquerels of cesium-137 (1 PBq = 10(15) Bq) were released during and subsequent to the accident.

A Model for Global Cycling of Tritium

Dynamic compartment models are widely used to describe global cycling of radionuclides for purposes of dose estimation. In this paper, we present a new global tritium model that reproduces environmental time-series data on concentrations in precipitation, ocean surface waters, and surface fresh waters in the northern hemisphere, concentrations of atmospheric tritium in the soutehrn hemisphere, and the latitude dependence of tritium in both hemispheres. Named TRICYCLE for Tritium CYCLE, the model is based on the global hydrologic cycle and includes hemisphereic stratospheric compartments, disaggregation of the troposphere and ocean surface waters into eight latitudezones, consideration of the different concentrations of atmospheric tritium over land and over the ocean, and a diffusive model for transport in the ocean. TRICYCLE reproduces the environmental data if we assume that about 50% of the tritium from atmospheric weapons testing was injected directly into the northern stratosphere as HTO. The models latitudinal disaggregation permits taking into account the distribution of population. For a unfiormaly distributed release of HTO into the worldwide troposphere, TRICYCLE predicts a collective dose commitment to the world population that exceeds the corresponding prediction by the NCRP model by about a factor of 3. 11 refs., 5 figs., 1 tab.

Modelling atmospheric dispersal of the Chernobyl release across Europe

At the time of the Chernobyl accident little was known about the magnitude and time pattern of the release from the damaged reactor. This paper describes the detective work done in the weeks following the accident to assess the release and its dispersal across Europe; also calculations done since the USSR presentations in Vienna at the end of August 1986 and some estimates of longer term collective dose commitment. To conclude some general remarks are made about the implications of the Chernobyl accident for technical support in emergency procedures for any future nuclear accident.

Statistical evaluation of releases of C-14 from the Vienna Triga reactor

Recently the releases of C-14 from different sources gained increasing interest. This is because this radionuclide contributes with its long half life significantly to the collective dose commitment. Measurement of the release rate of C-14 as CO2 were carried out from 1979 to 1984 at the Vienna Triga reactor. These results show large differences. Due to the large number of available data, a statistical evaluation of data seem promising. This evaluation has shown that the releases fit quite well a normal distribution, indicating that the release of C-14 as CO2 from a TRIGA reactor is a random process.

Global and Local Effects of14C Discharges from the Nuclear Fuel Cycle

The radiologic impact of14C produced by the nuclear fuel cycle is assessed at both global and local levels. In the former context, it is predicted here that the specific activity of atmospheric CO2in the year 2050 will be ca 7.6 pCig-1C. Although this is similar to the present level, the subsequent collective dose commitment could be highly significant.The enhancement of14C concentrations around the nuclear fuel-reprocessing plant at Sellafield (Windscale) in Cumbria, U K has been monitored over recent years. For example, maximum levels of 27.2 pCig-1C (∼350% above natural) during 1984 were observed < 1 km from the plant, with enhanced activities detectable to at least 29km. Nevertheless, it is clear that the radiologic significance to the local population is low. The spatial distribution of the excess14C allows atmospheric dispersion models to be tested in the context of continuous releases and the results thus far show that the Gaussian plume model performs successfully.

A box model for calculation of collective dose commitment from radioactive waterborne releases to the baltic sea

To meet the new regulations of maximum yearly releases from Swedish nuclear power plants issued by the Swedish National Radiation Protection Institute, and to make realistic calculations of collective dose commitment derived from radionuclides discharged to the Baltic Sea, a box model AQUAPATH-BALTIC has been developed. The model calculates radionuclide concentrations in 25 boxes for discharges into given compartments and takes into consideration the dispersion rates of the water masses, the sediment-water interaction and radioactive decay. The calculated concentrations in water and sediment at steady state are then used to evaluate individual and collective intakes of activity and external exposures. The radiation doses to the global population following discharges to the Baltic Sea are also calculated.