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The potential harm of long-lived radionuclides estimated as the product of the activity of a radionuclide and the dose coefficient is examined. The potential harm of actinides in high-level wastes is calculated taking account of the harm due to their decay products. At the same time, an analogous calculation is performed for the uranium isotopes 238 U, 235 U, and 234 U consumed in the reactor. The value obtained, which depends on the time, can be regarded as the averted harm. The time for establishing radiation equivalence between the high-level wastes and the consumed uranium is determined as the time in which the potential harm from actinides becomes equal to the averted harm. It depends on the holding time of the spent fuel before radiochemical reprocessing. For a 5 yr holding period, it is ~49000 yr.In [1], it was proposed that the potential harm due to long-lived radionuclides in high-level wastes be estimated as the product of the activity of a radionuclide by its dose coefficient, showing the dose which an adult person would obtain if 1 Bq of this radionuclide entered the stomach. Six radionuclides were separated from high-level wastes which remain dangerous to humans for periods longer than 100,000 yr: 99 Tc and 129 I among fission products and 239 Pu, 240 Pu, 241 Am, and 243 Am among transuranium elements [2]. However, this conclusion was drawn neglecting the products of decay of long-lived radionuclides and the holding time of spent nuclear fuel before radiochemical reprocessing. This deficiency is eliminated in the present paper.In a reactor, not only are dangerous radionuclides produced but uranium isotopes 238 U, 235 U, and 234 U are consumed, which results in a decrease of the overall radiation hazard as a result of these radionuclides and the products of their decay. Consequently, for the radioisotopes 238 U, 235 U, and 234 U consumed in a reactor it is desirable to perform a similar calculation of the radiation hazard, which can be regarded as an averted harm, which depends on the time. Then the time for establishing radiation equivalence can be determined as the time when the potential hazard from radionuclides in high-level wastes becomes equal to the potential hazard of the consumed uranium radionuclides, i.e., to the averted harm.Actinides in High-Level Wastes. Table 1 gives the composition of the spent nuclear fuel from a VVÉR-440 reactor with initial enrichment 3.6% and burnup 33.4 kg/ton [3]. Although other degrees of enrichment and burnup are used at the present time, we shall consider these conditions to be model conditions which make it possible to develop a scheme for calculating the potential hazard of long-lived radionuclides from high-level wastes and radionuclides which have been burned up in a nuclear reactor. In so doing, we shall take account of the fact that in radiochemical reprocessing of spent nuclear fuel 0.01% of the uranium, 0.025% of the plutonium, and 0.5% of the neptunium [4] and all isotopes of americium and curium
The potential harm of long-lived radionuclides estimated as the product of the activity of a radionuclide and the dose coefficient is examined. The potential harm of actinides in high-level wastes is calculated taking account of the harm due to their decay products. At the same time, an analogous calculation is performed for the uranium isotopes 238 U, 235 U, and 234 U consumed in the reactor. The value obtained, which depends on the time, can be regarded as the averted harm. The time for establishing radiation equivalence between the high-level wastes and the consumed uranium is determined as the time in which the potential harm from actinides becomes equal to the averted harm. It depends on the holding time of the spent fuel before radiochemical reprocessing. For a 5 yr holding period, it is ~49000 yr.In [1], it was proposed that the potential harm due to long-lived radionuclides in high-level wastes be estimated as the product of the activity of a radionuclide by its dose coefficient, showing the dose which an adult person would obtain if 1 Bq of this radionuclide entered the stomach. Six radionuclides were separated from high-level wastes which remain dangerous to humans for periods longer than 100,000 yr: 99 Tc and 129 I among fission products and 239 Pu, 240 Pu, 241 Am, and 243 Am among transuranium elements [2]. However, this conclusion was drawn neglecting the products of decay of long-lived radionuclides and the holding time of spent nuclear fuel before radiochemical reprocessing. This deficiency is eliminated in the present paper.In a reactor, not only are dangerous radionuclides produced but uranium isotopes 238 U, 235 U, and 234 U are consumed, which results in a decrease of the overall radiation hazard as a result of these radionuclides and the products of their decay. Consequently, for the radioisotopes 238 U, 235 U, and 234 U consumed in a reactor it is desirable to perform a similar calculation of the radiation hazard, which can be regarded as an averted harm, which depends on the time. Then the time for establishing radiation equivalence can be determined as the time when the potential hazard from radionuclides in high-level wastes becomes equal to the potential hazard of the consumed uranium radionuclides, i.e., to the averted harm.Actinides in High-Level Wastes. Table 1 gives the composition of the spent nuclear fuel from a VVÉR-440 reactor with initial enrichment 3.6% and burnup 33.4 kg/ton [3]. Although other degrees of enrichment and burnup are used at the present time, we shall consider these conditions to be model conditions which make it possible to develop a scheme for calculating the potential hazard of long-lived radionuclides from high-level wastes and radionuclides which have been burned up in a nuclear reactor. In so doing, we shall take account of the fact that in radiochemical reprocessing of spent nuclear fuel 0.01% of the uranium, 0.025% of the plutonium, and 0.5% of the neptunium [4] and all isotopes of americium and curium
The radiation resistance of epoxy compounds, solidified by crystalline hardening agents -metaphenylenediamine and phthalic anhydride -is investigated. It is shown that under conditions of γ irradiation (E = 1.33 MeV) the temperature of vitrification of the compounds depends on the dose (doses up to 1500 Mrad were investigated) and temperature 20-160°C, and the radiation gas release depends on the vitrification temperature and irradiation. It is shown that epoxy-phthalic anhydride compound is best as a matrix for immobilizing solid radioactive wastes at high temperatures (80-130°C). The experiments showed that the proposed compound can be recommended for immobilizing solid radioactive wastes.A great deal of attention is now being devoted to choosing the compounds for immobilizing radioactive wastes [1][2][3]. Epoxy compounds are promising materials for handling wastes, because such compounds possess high radiation resistance due to their content of aromatic groups [1]. The possibility of fixing radionuclides in reactor graphite by an epoxy oligomer, whose density was increased by heterocyclic aldehyde of the furan series with a filler and special-purpose additive, was demonstrated first in our country. The solidifying agents used for epoxy compounds are characterized by a crystalline and liquid aggregate state and radiation resistance. Solidifying agents such as polyethylene polyamine and polyamides are used, for example, in the immobilizing agent F and the Atomik compound, whose operational properties are described in [1]. The compounds of these solidifying agents are convenient to use because they do not require additional heating. However, the relatively low vitrification temperature (~60°C) gives rise to difficulties in using such compounds for immobilizing solid wastes, whose radiation heating exceeds 60°C. If the temperature of radiation heating exceeds 80°C, it has been suggested that compounds undergoing hot solidification be used, and metaphenylenediamine (a crystalline substance with a melting temperature of 63°C) and phthalic anhydride (a crystal substance with melting temperature 130°C) be used as the solidifying agent [4]. The wastes are solidified at temperatures not less than the melting temperature of the solidifying agent. Then the compound is in a low-viscous state and when solid wastes are immobilized it penetrates into the microcavities, forming a reliable matrix.The immobilizing agents for solid wastes must meet the following basic requirements: they must have high mechanical and adhesion strength, they must remain stable in water solutions, including solutions of acids and alkali, they must be in a glassy state under operating conditions, leaching of radionuclides should not exceed 10 -4 g/(cm 2 ·day), and the gas release should be minimal (not greater than 10 -8 -10 -9 cm 3 /(g·rad)). Under operating conditions, the deviation of the first four parameters should not decrease by more than 25%.The experiments showed that solidified epoxy compounds in a glassy state have high strength under comp...
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