Reactivity management and burn-up management on JRR-3 silicide-fuel-core

Kato, Tomoaki; Araki, Masaaki; Izumo, Hironobu; Kinase, Masami ; Torii, Yoshiya ; Murayama, Yoji

On the conversion from aluminide fuel to silicide fuel, burnable absorbers were introduced for decreasing excess reactivity. The burnable absorbers influence reactivity during reactor operation. So, the burning of the burnable absorbers was studied and the influence on reactor operation was made cleared. Furthermore, necessary excess reactivity on beginning of operation cycle and the time limit for restart after unplanned reactor shutdown was calculated. After the conversion, the fuel exchange procedure was changed from the six-batch dispersion procedure to the fuel burn-up management procedure. The previous estimation of fuel burn-up was required for the planning of fuel exchange, so that the estimation was carried out by means of past operation data. Finally, a new fuel exchange procedure was proposed for effective use of fuel elements. The average length of fuel-staying in the core can be increased by two percent on the procedure.