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 ²³⁵U(n,f) and ²³⁹Pu(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 ²³⁹Pu, ²⁴⁰Pu, ²⁴¹Pu, ²⁴²Pu, ²³⁷Np, ²³⁵U, and ²³⁶U 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 ⁹⁰Sr, ¹⁰⁷Pd, ¹³⁵Cs, and their isobars ⁹⁰Rb, ¹⁰⁷Rh, and ¹³⁵Xe 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.