Investigation of burnable poisons effects in reactor core design

Burnable absorber rods (BAR) and chemical shim are the main control poisons that are used in the core for improving the reactor behavior and satisfying the safety criteria during the core life time. These poisons have several constraints, criteria, advantages and also disadvantages from the safety and operation points of view; and these characteristics depend on the concentration and distribution of mentioned poisons in the reactor core. Therefore, understanding their effects on the reactor core behavior, especially the mutual interaction between them, is a crucial issue in reactor core design procedure. In this study, the influences of the burnable poisons on the main parameters of the reactor such as multiplication factor, burnup, soluble poison concentration, moderator temperature coefficient and power peaking factor over the reactor life time are investigated. The VVER-1000 reactor was selected for this investigation.The reactor core was modeled by WIMS and CITATION codes. Several different loading patterns based on different distributions and concentrations of BARs were defined. Subsequently, the main parameters of the core for each pattern were calculated by the core model and were investigated to analyze the effects of BAR concentration and distribution on the reactor behavior.The presented results made it possible to analyze and understand the BAR and chemical shims effects on the behavior of the nuclear reactor core.

► In this study, the influences of burnable poisons on the main parameters of a reactor are investigated. ► Based on the performed research, the mutual effects of chemical shim and BAR in the core could be realized. ► Based on the presented results, the effect of BAR can be quantified and used in the design of a reactor core.