Optimization of Core Reload Design for Low-Leakage Fuel Management in Pressurized Water Reactors

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Abstract
A method was developed to optimize pressurized water reactor low-leakage core reload designs that features the decoupling and sequential optimization of the fuel arrangement and control problems. The two-stage optimization process provides the maximum cycle length for a given fresh fuel loading subject to power peaking constraints. In the first stage, a best fuel arrangement is determined at the end of cycle (EOC) in the absence of all control poisons by employing a direct search method. The constant power, Haling depletion is used to provide the cycle length and EOC power peaking for each candidate core fuel arrangement. In the second stage, the core control poison requirements to meet the core peaking constraints throughout the cycle are determined using an approximate nonlinear programming technique. For the core description, the design method utilizes a currently recognized licensing-type code, SIMULATE-E, that was adapted to the CYBER-205 computer. The methodology was applied to the core reload design for cycles 9 and 10 of the Commonwealth Edison Company (CECo) Zion-1 reactor. The results showed that, compared with the reference design used by CECo, the optimum loading pattern for cycle 9 yielded almost a 9% increase in the cycle length while reducing core vessel fluence by 30%. Cycle length increase is a direct measure of economic savings for a given fuel loading. The results of cycle 10 optimization produced similar improvements. Should cycle length constraints apply, the procedure could be used to yield a decrease in fuel enrichment, with comparable savings resulting.