Void reactivity analysis on high temperature fast reactor

Otani, Nobuo*

Core physics was studied on the High Temperature Fast Reactor (HTFR) whose prime objective is to produce hydrogen. Core of HTFR consits of nitride or oxide fuel, and thermal power of a commercial HTFR is assumed to be 300 to 400 MWt. The analysis in this report aims at the core design having negative or small positive void reactivity from view point to attain safety if the reactors, The method of decreasing sodium void reactivity coefficient was to increase neutron leakage through the large surface area of the core by adopting its shape of a pan cake (core height/core diameter=1/2 to 1/3). Result of the analysis revealed that, total void coefficients is negative for all cases analyzed with U fuel. However almost all the cases analyzed had positive void reactivity coefficients for MOX fuel. Burn-up calculation was peformed for U fuel core. Calculational results showed that the excess reactivity of about 5% was necessary to compensate reactivity decrease due to the burn-up during a year. The above calculations were performed using the CITATION code.