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(Zmodel) to obtain the isotope yields in theU(n,f) andPu(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 forU, the contents ofPu,Pu,Pu,Pu,Np,U, andU 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 nuclidesSr,Pd,Cs,and their isobarsRb,Rh, andXe 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.