Study on Neutronic Performance Evaluation Method of Burnable Poisons

Burnable poisons (BPs) play a critical role in reactivity control for small long-lifetime pressurized water reactors (PWRs). However, traditional evaluation methods are subjective and one-dimensional, which cannot fully capture their multi-stage neutronic performance. Methods: A multi-dimensional evaluation system was established to cover the initial, middle, and end stages of the burnup cycle. Six key evaluation indices were selected, including initial reactivity suppression, end-of-cycle burnup reduction, maximum reactivity peak, integral area of supercritical residual reactivity, reactivity integral area difference with/without BP, and BP burnout rate, and their quantitative models were defined. The CRITIC method was adopted to determine the objective weights of the indices. Burnup calculations for ten typical BP materials (B4C, Gd2O3, Er2O3, Dy2O3, Eu2O3, Sm2O3, 231Pa, 237Np, 240Pu, 241Am) were performed using the DRAGON code to verify the evaluation system. Results: The weights of initial reactivity suppression, maximum reactivity peak, and BP burnout rate were 0.2332, 0.2190, and 0.2019, respectively, which are the key factors affecting the comprehensive performance of BP. 231Pa exhibited the best comprehensive performance with no end-of-cycle burnup reduction and increased burnup depth. B4C and Gd2O3 showed excellent initial reactivity suppression and smooth reactivity release. Dy2O3 and Eu2O3 had poor comprehensive performance due to significant end-of-cycle reactivity penalties.