Abstract
This study investigated the PWR burnup credit effect using the nuclide sensitivity method. From a typical PWR spent nuclear fuel, the method started with selecting the top 20 nuclides with significant macroscopic neutron absorption cross sections, which are expected to have potential effect on the system multiplication factor. After that, the sensitivity of each nuclide to the system multiplication factor at various cooling times was evaluated using the MCNPX Monte Carlo transport code. This method can be used to estimate the spent fuel burnup credit effect and identify what nuclides cause the difference. This study quantitatively analyzed the burnup credit effect of several PWR fuel depletion parameters, including initial enrichment, specific power, operation history, boron concentration, fuel temperature, moderator temperature, control rods effect, and axial power distribution. Compared to direct criticality calculations of spent nuclear fuel, two major advantages of the nuclide sensitivity method are: (1) The criticality safety of spent fuel can be examined in depth in terms of their characteristics and compositions; (2) The method can give quantitative estimate of the contribution of each nuclide in the spent fuel to the system multiplication factor.