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(Zp 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 238U,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 crosssections.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.