DESIGN AND SAFETY ASPECT OF LEAD AND LEAD-BISMUTH COOLED LONG-LIFE SMALL SAFE FAST-REACTORS FOR VARIOUS CORE CONFIGURATIONS

Design and safety aspects of long-life small safe fast reactors using liquid lead or lead-bismuth coolant with metallic or nitride fuel are discussed. Neutronic analyses are performed to investigate the effect of core height to diameter ratio (H/D) on design performance of the pr oposed reactors. All reactors are subjected to the constraint of 12 ye ars operation without refueling and shuffling with constant 150 MWt re actor power and also to the requirement of maximum excess reactivity d uring burnup to be less than 0.1%Delta k. The results show that the pa ncake design with H/D of similar to 2/3 gives the most negative coolan t void coefficient under the requirements for excess reactivity. Modif ied designs with the central region axially fulfilled with fertile mat erial are proposed to improve the coolant void coefficient. Thermal-hy draulic analysis results show the possibility to operate the reactors up to the end of life without changing their orifice pattern, necessar y pumping power for the proposed design smaller than the conventional large sodium cooled FBR, and the natural circulation contribution of 2 5-40% at the normal operating condition. The reactivity feedback coeff icients are also estimated and appeared to be negative for all the com ponents including the coolant density coefficient.