Investigation of different burnable absorbers effects on the neutronic characteristics of PWR assembly

Abstract

There is an urgent need to find compact burnable BA materials as an alternative to the traditional materials (B4C and Ag-In-Cd). These materials must possess higher density, good thermophysical properties, radiation resistance, and swelling resistance. In this article, the most interesting rare earth nuclides for neutron absorption (gadolinium, erbium, dysprosium, hafanium and dysprosium) are studied and compared from the point of view of their possibilities for the control of core reactivity in PWRs to increase the cycle length. MCNPX code is used to design a three dimensional model for PWR assembly. The PWR assembly is loaded in different operation process with 2% Gd2O3 and 2% Er2O3 as integral burnable absorbers (IBAs). The effects of gadolinia and erbia on the thermal neutron flux and normalized power are investigated. The study presents that erbium is more effective IBA than gadolinium for a reactor with a very long cycle. The dysprosium titanate, dysprosium hafnate and hafnium diboride are investigated as material for a control rod in PWR assembly. The effects of these control rod materials on the multiplication factor and the concentrations of fission products are calculated. From the viewpoint of the achievable fuel discharge burnup, it was found that the suggested control rod materials achieve a satisfactory control rod worth (CRW), i.e., the CRW of the presented materials is comparable with the CRW of the standard AIC control rods.