Physical Analysis of Control Rod Structure in Pressurized Water Reactor

Abstract

Reactivity control is an important field of reactor research, and control rod is one of main way of reactivity control. Currently, in order to improve the safety of some new reactors, boric acid is eliminated as a means of reactivity regulation, and the loss of controlled reactivity is compensated by increasing the reactivity value of control rods. The reactivity value of control rod is related to its size and structure. In this paper, the reactivity value of cylindrical
control rod and cross shaped control rod in PWR is calculated by using a Monte Carlo code, and the influence of two kinds of control rods on the core reactivity under the same volume and the same neutron irradiation area, and the relationship between the geometry size of cross shaped control rods and the core reactivity are analyzed. The results show that the reactivity value of control rod is directly proportional to its volume and neutron irradiation area; with the same volume of control material, the reactivity value of cross shaped control rod is higher; with the same neutron irradiation area, the reactivity value of cylindrical control rod is higher; when the reactivity value is the same, the volume of cross shaped control rod is smaller, about 75% of the volume of cylindrical control rod, which provides a new idea for the study of reactivity control scheme without boric acid.