Evaluation of the specific radioactivity of 40 elements created by nuclear transmutation of fission products

Abstract

A burnup calculation was performed to analyze Après ORIENT process which aims at creating highly-valuable elements by nuclear transmutation of fission products (FPs) separated from LWR spent nuclear fuels. In this paper, numerical evaluation of the specific radioactivity of 40 created elements, from reloaded each FP element, with atomic number from 31 to 70 at the end of the time of 5-year-cooling after the irradiation for 1125 days in each LWR and FBR was carried out. These 40 created elements were classified in 6 categories according to levels of the specific radioactivity and the length of additional cooling period, which was needed for the specific radioactivity to decrease below the exemption level defined by International Atomic Energy Agency. As a result, created 31Ga, 32Ge, 33As, 35Br, 68Er, and 70Yb did not contain any radioisotopes at the end of the 5-year-cooling. It should be noted that created 37Rb, 57La, and 60Nd had much lower specific radioactivities than natural composition of them. Moreover, specific radioactivities of created 40Zr, 42Mo, 44Ru, 46Pd, 49In, and 54Xe were sufficiently lower than their exemption levels at the end of the 5-year-cooling. On the other hand, created 39Y, 45Rh, 50Sn, 52Te, 58Ce, 59Pr, 65Tb, and 66Dy needed additional cooling period less than 10 years until their specific radioactivities decreased below their exemption levels. Then, each additional cooling period required for created 48Cd, 51Sb, 64Gd, and 69Tm was estimated at 10–100 years. Additionally, specific radioactivities of other 13 created elements would not decrease below their exemption levels even if they had been stored for 100 years. There could be significance to create important elements as resources classified in first 4 of the 6 categories defined in this paper, by nuclear transmutation of fission products. In consideration of the efficiency of creation, the radioactivity, and the importance as resources of each product, 44Ru, 46Pd, 52Te, 60Nd, and 66Dy were specially selected as the most important created elements to be more researched in the future Après ORIENT program.