Design of transition cycles to extend cycle length to 24 months in BWR reactors

Starting with an operating cycle of 18 months, four transition cycles were designed to reach equilibrium conditions based on a 24-month operation for a boiling water reactor. Pre-designed fuel assemblies for a typical BWR-5 reactor were used for the design of the refueling. In a first stage of development, the Haling principle was used to calculate the conditions at the end of the operating cycle and thus determine the burnout of the fuel assemblies. This paper presents a comparison of 3 fresh fuel load fraction scenarios to reach the 24-month cycle: 180, 184 and 188 fresh assemblies each with two levels of uranium enrichment. In terms of the burn-to discharge analysis, the scenario with the best fuel use is that of the load fraction of 188 assemblies. However, this scenario has the drawback of requiring more fuel assemblies than the others. In terms of the fuel purchase, the scenario of 180 assemblies is the one that represents the best option, but has the disadvantage of using less uranium than the other options. Therefore, according to the conditions in which this study was carried out, the best scenario is that of 184 fresh assemblies since it represents an intermediate scenario between the fuel purchase and the uranium use. (author)