Using a combination of weighting factor method and imperialist competitive algorithm to improve speed and enhance process of reloading pattern optimization of VVER-1000 reactors in transient cycles

In this research, an innovative solution is described which can be used with a combination of the new imperialist competitive algorithm and the weighting factor method to improve speed and increase globality of search in reloading pattern optimization of VVER-1000 reactors in transient cycles and even obtain more desirable results than conventional direct method. In this regard, to reduce the scope of the assumed searchable arrangements, first using the weighting factor method and based on values of these coefficients in each of the 16 types of loadable fuel assemblies in the second cycle, the fuel assemblies were classified in more limited groups. In consequence, the types of fuel assemblies were reduced from 16 to 6 and consequently the number of possible arrangements was reduced considerably. Afterwards, in the first phase of optimization the imperialist competitive algorithm was used to propose an optimum reloading pattern with 6 groups. In the second phase, the algorithm was reused for finding desirable placement of the subset assemblies of each group in the optimum arrangement obtained from the previous phase, and thus the retransformation of the optimum arrangement takes place from the virtual 6-group mode to the real mode with 16 fuel types. In this research, the optimization process was conducted in two states. In the first state, it was tried to obtain an arrangement with the maximum effective multiplication factor and the smallest maximum power peaking factor. In the second state, the objective of optimization was to obtain a reloading pattern with the most flattened thermal power distribution. Using the method proposed in this paper, the optimum arrangement was obtained almost 2.5 times quicker than the conventional direct method. In addition, optimality of the arrangements obtained from this method was higher than the conventional direct method and even the pattern proposed by Russian contractors. However, it is worth mentioning that the method proposed in this research is not solely limited to the imperialist competitive algorithm and it is possible to use other meta-heuristic smart algorithms with the proposed solution. Finally, to calculate the objective parameters more precisely during evaluation of arrangements and examine their desirability during an operational cycle length, a computational thermo-neutronic coupling was designed using the WIMSD5-B and CITATION-LDI2 codes in the neutronic section and the WERL code in the thermohydraulic part.