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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

Perovskite-based ceramics ABO3 (A = La or Gd; B = Al or Fe) and a pseudobinary system: LaAlO3 + CaZrTi2O7 are promising matrices for immobilization of actinide fraction of HLW. The ceramic samples containing 241Am, 238Pu or 147Pm were prepared by cold pressing in pellets at 100–300 MPa and sintering at 1300–1500 °C. Leach rates of radionuclides and matrix elements (La, Gd, Al and Fe) from powders were measured using Soxhlet unit. Sintered ceramics in the series: LaAl1-xFexO3 were composed of perovskite phase. Ceramics in the compositional series xLaAlO3 + CaZrTi2O7 (0.4 ≤ x ≤ 6) consisted of perovskite, zirconolite, and baddeleyite at x = 0.4 and x = 0.7, and perovskite and baddeleyite at higher x values. Leach rate of radionuclides and matrix elements from all the ceramics were lower than 10-8 g·cm-2·day.