Evaluation of Migration Radiological Equivalence for Dual Component Nuclear Waste in a Deep Geological Repository.

ABSTRACT: The paper is concerned with the issue of achieving the radiological equivalence (the equivalence of radiation risks) of radioactive waste of nuclear reactors and corresponding mass of natural uranium, taking into account the different migration ability of radionuclides in geological formations and soil. This migration radiological equivalence is being investigated for the deep burial of radioactive waste in the case of the development of a two-component nuclear power system with the concurrent use of thermal neutron reactors and fast neutron reactors. Calculations were performed of radiation doses and radiation risks of cancer death arising from consumption of drinking water from a well above a disposal site. The radiation risk relating to a two-component nuclear power system is lower than that from natural uranium; i.e., after reaching the radiological equivalence (100 y of storage) over the timescale of 109 y, the principle of migration radiological equivalence is satisfied. It would take 106 y after radioactive waste disposal to reach the migration radiological equivalence if only thermal reactors were operated. As regards consumption of well drinking water, the radiation risk does not exceed 10-5 y-1 for a two-component nuclear power system, while being 10-3 y-1 (socially unacceptable level) for a power system using only thermal reactors. Radionuclides 241Am, 239Pu, and 240Pu in drinking water make the main contribution to the doses and radiation risks of people for 104 y after the disposal of radioactive waste.

[Forecasting model of transfer of 137Cs to the plants].

The forecasting model of the concentration ratio (CR) of 137Cs in the plants taking into consideration organic carbon, pH, mobile and total content of potassium in soil has been developed on the basis of the radioecological investigations in the valleys of the Resseta and Vytebet rivers. The type of functional dependence of CR from soil characteristics can be used for an estimation of the content of radionuclides in various species and productive parts of plants.

[The method for calculation the dose absorbed by terrestrial animals for assessments of the environmental impact from radioactive contamination].

The method for calculatior of the exposure doses to terrestrial animals in areas contaminated by radionuclides using a point source dose function is presented. To take into account scattered gamma-radiation, the Berger formula for dose buildup factor in an infinite air medium has been parameterized. In developed dosimetric model, an animal phantom is presented as parallelepiped to estimate external dose exposures and as a tissue equivalent sphere to estimate internal doses. Using the analytical expressions, dose rate conversion coefficients for external and internal exposures of animals have been estimated for individual radionuclides. For energies of gamma-rays, the results are found to be in good agreement with those estimated by the Monte-Carlo method for the ellipsoidal phantoms of animals.

[Actual problems of ecological dosimetry].

Different methodological approaches are analyzed for developing the environmental protection system with respect to biota, as well as the state-of-the-art of dosimetric studies on the assessment of radiological consequences on biota in the contaminated environment. Factors are enumerated that the influence quality of dosimetric models. The need for consideration of radiobiological and biological peculiarities of organisms in dosimetric models is stressed.

[The transfer of 90Sr and of 137Cs radionuclides in the chain of soil-fodder-animal products in the area contaminated as a consequence of the Chernobyl AES accident].

The database on 137Cs and or 90Sr transfer factors in the soil-fodder-animal products chain compiled in the framework of the project "Radioecological Consequences of the Chernobyl Accident" under the French-German Initiative was analyzed. The 137Cs transfer factors were determined into 10 fodder types for farm animals. The 137Cs and 90Sr transfer from daily diet to milk is practically independent from milk yield and season and is about 0.83% and 0.16%. 137Cs transfer factor into beef (adult animals) is about to 2.4% from the daily uptake with fodder per 1 kg meat.

[A mathematical model of 137Cs uptake and removal from the body of cattle in the event of chronic consumption of contaminated fodder].

A two-chamber mathematical model of 137Cs uptake and removal from the body of cattle chronically consuming contaminated fodder has been developed; the model takes into account age dependence of radionuclide absorption from the gastro-intestinal tract. The model parameters were taken from the experiment on calves with chronic peroral uptake of contaminated fodder. In accordance with the model and experiment, 137Cs transfer factor to the muscular tissue one month after birth reaches a maximum value of 56% of the daily uptake per 1 kg of the tissue. By the model, the equilibrium processes of uptake and removal set in two years after the calves birth. The equilibrium TF for muscles in adults approximates 2.8% of the daily uptake per 1 kg tissue. Because of 137Cs absorption from the gastrointestinal tract changes with age, doses of internal exposure of calves over the first two years will be about 5 times higher than doses for any one of the two subsequent years.

[A comparative analysis of the impact on biota and man in the 30 km zone of the Chernobyl NPP]. / Sravnitel'naia otsenka radiatsionnogo vozdeistviia na biotu i cheloveka v 30-kilometrovoi zone Chernobol'skoi AES.

A methodological approach is described for a comparative assessment of ionizing radiation effects on man and biota, based on the use of indices of radiation impact--ratios of actual exposure doses to environmental objects (including humans) and critical ones. As such doses, standards limiting radiation exposure and doses at which phenotypical effects were absent after the Chernobyl accident were employed, respectively for man and biota. For the test site chosen within the 30 km ChNPP zone (region of the Borshchovka settlement), dose burdens to reference biota species and the population (with and without evacuation) and the corresponding radiation impact indices were calculated. For the long term period after the accident radiation safety standards for man are shown to ensure radiation safety for biota as well. At the same time in the early period after the accident the emergency regulations do not guarantee adequate protection of nature, some species of which can be subject to irradiation more than man, even if countermeasures like evacuation are not applied. A conclusion has been made on the necessity of a more detailed and comprehensive analysis of situations when the anthropocentric principle "if radiation standards protect man then biota are also adequately protected" is violated.

[Reconstruction of I-131 in milk and exposure doses to the thyroid gland of cattle after the Chernobyl AES]. / Rekonstruktsiia soderzhaniia 131I v moloke i doz oblucheniia shchitovidnoi zhelezy krupnogo rogatogo skota posle avarii na ChAES.

Suggestions are made concerning the restoration of 131I content in cow milk of six districts in the Gomel region based on radiometric measurements of the overall activity of milk samples in the iodine period of the Chernobyl NPP accident, reconstruction of doses to thyroid of cattle and calculation of dose distribution among the live-stock by separation the function of activity changes in milk samples in time into the basic components formed by the contribution of 131I, 134Cs and 137Cs. The best approximation to the description of the function of milk activity variations was found to be achieved by the representation of forage activity changes as a sum of exponents with the half-life periods of 5 and 30 day with a partial contribution of 0.8 and 0.2. The calculations showed, that the average absorbed doses to the thyroid varied between 10 and 40 Gy.

[Effect of separate radioactive and chemical pollutants on the yield of cytogenetic disruptions in the intercalary meristem in spring barley]. / Vliianie razdel'nogo radioaktivnogo i khimicheskogo zagriazneniia na vykhod tsitogeneticheskikh narushenii v interkaliarnoiiiarovogo iachmenia.

Dependencies of the yield of cytogenetic disturbances within intercalary meristem cells of spring barley on the soil level of 137Cs (1.48-14.8 MBq/m2), Cd, Pb (2-50 and 30-300 mg per kilogram of the soil) and 2.4-D herbicide (1 or 2 kg/ha) had a non-linear character in the studied range. At low concentrations the yield of cytogenetic disturbances grew faster than at higher ones. Concentrations of lead in soil (at the level of maximum concentration limit) and doses of 2.4-D recommended for agricultural use resulted in the increase in the rate of aberrant cells. The observed rate of cytogenetic disturbances was comparable with the effect of the maximum studied level or the radioactive soil pollution. The heaviest damage to aberrant cells was found in the presence of 137Cs.

[Radiation safety of the population and agricultural production industry (standardization of the radionuclide content of agricultural products)]. / Radiatsionnaia bezopasnost' naseleniia i agropromyshlennoe proizvodstvo (k voprosu o normirovanii soderzhaniia radionuklidov v sel'skokhoziaistvennoi produktsii).

The topical problems of standardization of the radionuclide content in food products and radiation control in agricultural production have been considered. The fundamental principles for establishing the permissible radionuclide concentrations in foodstuffs and acceptable contamination levels of agricultural land and products were justified.

[An analysis of the cytogenetic sequelae of chronic low-dose irradiation in plantings of agricultural crops]. / Analiz tsitogeneticheskikh posledstvii khronicheskogo oblucheniia v malykh dozakh posevov sel'skokhoziaistvennykh kul'tur.

There is a tendency for a decrease in the yield of cytogenetic disturbances with time elapsed from the Chernobyl accident. But an increased rate of cytogenetical damages significantly dependent on the level of radioactive contamination was observed even in several years after the incident. The rate of decline with time in cytogenetic disturbances induced by chronic exposure considerably lagged behind that of radiation exposure. Analysis of genetic changeability in three sequential generations of winter rye and wheat revealed increased cytogenetic damage in crops grown on contaminated sites during 2 and 3 years.

[The build up of absorbed doses in the critical organs of cereal grains in a contaminated area after the accident at the Chernobyl Atomic Electric Power Station]. / Formirovanie pogloshchennykh doz v kriticheskikh organakh khlebnykh zlakov na zagriaznennoi territorii posle avarii na Chernobyl'skoi AES.

The calculation method for absorbed doses of ionizing radiations in critical organs of cereals during the first vegetation period after the ChNPP accident is presented. Calculation of radiation burden on plants nearly 5 settlements in the 30 km zone of ChNPP accident are carried out. gamma-radiation of radionuclide fallouts is demonstrated to give the main contribution into absorbed dose and dose ratio beta- to gamma-radiation varied within the range from 5 to 10 depending on radionuclide composition of fallouts.

[An analysis of the genetic sequelae of the contamination of winter rye crops by the radioactive fallout from the Chernobyl Atomic Electric Power Station]. / Analiz geneticheskikh posledstvii zagriazneniia posevov ozimoi rzhi radioaktivnymi vypadeniiami Chernobyl'skoi AES.

Changes of important cytogenetical indices, like an yield of aberrant cells and their burden by damages, with dose value was shown at the study of genetical consequences of winter rye contamination with radioactive Chernobyl NPP fallout at the acute phase (the vegetation period of 1986). Larger genetical efficiency was demonstrated for low dose rate radiation. Stimulation of morphometric indices in rye seedlings characterizing their survival on the earlier stages of ontogenesis was observed together with significant increase of the cytogenetical damages.