Estimating NIRR-1 burn-up and core life time expectancy using the codes WIMS and CITATION

Abstract

The Nigeria Research Reactor-1 (NIRR-1) is a low power miniature neutron source reactor (MNSR) located at the Centre for Energy Research and Training, Ahmadu Bello University, Zaria Nigeria. The reactor went critical with initial core excess reactivity of 3.77mk. The NIRR-1 cold excess reactivity measured at the time of commissioning was determined to be 4.97mk, which is more than the licensed range of 3.5–4mk. Hence some cadmium poison worth −1.2mk was inserted into one of the inner irradiation sites which act as reactivity regulating device in order to reduce the core excess reactivity to 3.77mk, which is within recommended licensed range of 3.5mk and 4.0mk. In this present study, the burn-up calculations of the NIRR-1 fuel and the estimation of the core life time expectancy after 10years (the reactor core expected cycle) have been conducted using the codes WIMS and CITATION. The burn-up analyses carried out indicated that the excess reactivity of NIRR-1 follows a linear decreasing trend having 216 Effective Full Power Days (EFPD) operations. The reactivity worth of top beryllium shim data plates was calculated to be 19.072mk. The result of depletion analysis for NIRR-1 core shows that (7.9947±0.0008) g of U-235 was consumed for the period of 12years of operating time. The production of the build-up of Pu-239 was found to be (0.0347±0.0043)g. The core life time estimated in this research was found to be 30.33years. This is in good agreement with the literature