Analysis of Large Liquid-Metal Fast Breeder Reactor Critical Experiments by Improved Methods

To solve the problems encountered in the analysis of the large homogeneous and heterogeneous fast critical assemblies, Zero-Power Plutonium Reactor (ZPPR) 9, 10, and 13, we have revisited the analysis using improved methods. Two-dimensional cell calculations, cell calculations using multidrawer cell models, and three-dimensional transport theory core calculations were introduced. Using these methods, the discrepancies in the calculation-to-experiment (C/E) values of k_eff for the fast critical assemblies was reduced. The use of the multidrawer model reduced the C/E spatial dependency of the control rod worths in the ZPPR-10 cores. To investigate the remaining problems of the spatial dependence of the C/E values of reaction rate distribution and control rod worth, we have adjusted a cross-section set obtained from the JENDL-2 library using the integral experiments. The cross-section changes, particularly for the diffusion coefficient, ²³⁸U scattering and capture, and ²³⁹Pu fission cross sections, have corrected the spatial dependence, as well as the overestimation of the ²³⁸U capture to ²³⁹Pu fission rate ratio and sodium void worth.