Theoretical analysis of long-lived radioactive waste in pressurized water reactor

Background The accelerator-driven subcritical transmutation system(ADS) is an advanced technology for the harmless disposal of nuclear waste. A theoretical analysis of the ingredients and content of nuclear waste, particularly long-lived waste in a pressurized water reactor(PWR), will provide important information for future spent fuel disposal.Purpose The present study is an attempt to investigate the yields of isotopes in the neutron-induced fission process and estimate the content of long-lived ingredients of nuclear waste in a PWR.Method We combined an approximation of the mass distribution of five Gaussians with the most probable charge model(Z_p model) to obtain the isotope yields in the~(235)U(n,f) and~(239)Pu(n,f) processes. The potential energy surface based on the concept of a di-nuclear system model was applied to an approximation using five Gaussian functions. A mathematical formula for the neutron spectrum in a PWR was established, and sets of differential equations were solved to calculate the content of long-lived nuclides in a PWR.Results The calculated isotopic fission yields were in good agreement with the experimental data. Except for~(238)U, the contents of~(239)Pu,~(240) Pu,~(241) Pu,~(242) Pu,~(237) Np,~(235) U, and~(236) U are predominant in the PWR after reaching a discharge burnup. In addition, some isotope pairs of heavy nuclei reach a similar value after stabilization, which can be explained by the decay chain and effective fission cross-sections. For fission fragments, we simulated the content evolution of some long-lived nuclides~(90) Sr,~(107) Pd,~(135) Cs,and their isobars~(90) Rb,~(107) Rh, and~(135) Xe during a fuel cycle in a PWR. The variations in the inventories of uranium and plutonium were in good agreement with the data in Daya Bay.Conclusion A new method is proposed for the prediction of the isotopic fission yield. The inventory of long-lived nuclides was analyzed and predicted after reaching a discharge burnup.

Nuclear Science and Techniques

2021年07期