Preparation for restarting the high temperature engineering test reactor: Development of utility tool for auto seeking critical control rod position

Abstract

At high power operation of the HTTR, the control rod should be kept at the top of the active core for maintaining the optimized power distribution so as to minimize the maximum fuel temperature. It is important to calculate the control rod position each time the operating conditions change in order to ensure the safe operation of the reactor. Since the Monte-Carlo code cannot change the core geometry such as control rod position during criticality and burnup calculation, the critical control rod position was determined by adjusting the control rods manually at each burnup step. This complicates the calculation procedures as well as prolongs the total time including calculation time, handling time, and waiting time. Therefore, this study develops a new utility tool that seeks the control rod position automatically without any further handling procedures and waiting time. As a result, the determination of critical control rod position becomes simpler and the total time was also reduced significantly from about 5 days to less than 2 days. The calculated critical control rod position using the new tool also gives a good agreement with the experiment data.