Optimization of depleted uranium loading in fresh core of large sized Indian PHWR by evolutionary algorithm

Pressurised Heavy Water Reactors (PHWRs) are based on Natural Uranium (NU) fuel and heavy water as moderator and coolant. At the beginning of reactor life of PHWR, if all NU bundles are loaded, the power peaking is high and full power cannot be drawn. In order to draw full power, it is possible to flatten the power in fresh core by loading some depleted uranium (DU) (or Thorium) bundles. The determination of the best possible locations of DU bundles which maximize economy and preserve safety is a constrained combinatorial optimization problem. This paper presents optimization of DU bundle distribution in the fresh core of the 700 MWe PHWR. An evolutionary technique based on Estimation of Distribution Algorithm (EDA) is used to determine the optimum DU loading pattern. The best suitable locations for DU bundles are determined using EDA. In order to meet some additional constraints, some additional DU bundles are placed at 11th and 12th bundle locations in few channels. These channels are selected manually. The overall aim of the optimization is to maximize K-effective and get 100% full power without violating safety parameters such as maximum permissible bundle power, channel power peaking factor and permitted reactivity worth in shut-down system. The optimum configuration is explicitly presented.