Nuclear Design Methodology for Spent Fuel Recycle without Reprocessing

Spent nuclear fuel management is one of the big question since nuclear power generation start. Especially, storage for spent fuel is an important issue in the side of both social and technical burden. The spent fuel pin composition retrieving methodology using a 2-step lattice/nodal code commonly used in PWR core simulations was presented by our team in Kyung Hee University [1, 2]. This study is an extension study of the previous research, and it is mainly divided into (1) validity check and improvement of proposed methodology, (2) production of spent fuel pin DB, (3) Establish spent fuel assembly re-construction methodology, and (4) Feasibility check of direct using with PWR reload core design. The spatial effect enough is not considered enough on spent fuel pin composition retrieving methodology which was proposed in previous research. Spatial effect was inspected by axial burnup effect and assembly internal location effect, respectively. Considering the effect of axial burnup, assembly-wise k-inf value did not differ greatly up to 100pcm through a cycle, and axial flux distribution was comparable, also. There was no significant difference in the composition of the isotope number density. On the other hand, considering the internal location effect of the assembly, the minimum difference between the existing method and 800pcm was 1300pcm on only one fuel assembly. In selecting the spent fuel pins to re-construct an assembly for direct recycling, burnup value was used only in the previous methodology. However, in this study, the η_burnup value of the spent fuel pin is used to measure the reactivity among the different types of spent fuel pins. The feasibility of the direct recycle with reload core design was tested by loading the reassembled spent fuel assemblies instead of the fresh fuel without changing the loading pattern of the reference core. As a result, the operating constraints satisfied all the conditions except the radial peaking factor. This value is comparable to the Fr value of the reference core, which would be sufficient to satisfy the operating constraint if the later optimization core is designed. The re-constructed fuel assembly can be loaded in one cycle only by the limitation of the burnup due to the maximum pin-wise burnup value in the re-constructed fuel assembly. Therefore, the spent fuel assemblies can be re-utilized during one cycle instead of fresh fuel. The loaded fresh fuel usually stays in the core for three cycles in OPR-1000 core. However, the re-constructed fuel assembly can only stay one cycle due to the limitation of the burnup. Thus, the re-constructed fuel assembly must not only replace only fresh fuel, but also replace the corresponding once burnt and twice burnt fuel assembly in follow-up cycle by newly re-constructed fuel assembly, respectively. the cycle length loss was not too large, and the operation restrict conditions were not violated except Fr value. The radial peaking factor was slightly exceeded the operating limit, but the exceeded value was quite small so that the optimized design could be mitigated below the operating limit in most cases. Therefore, it was possible to show the feasibility of the nuclear core design to directly with spent nuclear fuel reloading. The purpose of this study was to check the feasibility of directly recycling the spent nuclear fuel methodology into the reactor core. Thus, there was no design to be changed except the place where the spent fuel assemblies are loaded. If a core design that minimizes cycle length loss while satisfying all operating constraints through optimization design can be performed. Furthermore, a practical design of the equilibrium cycle core design with spent fuel re-loading can be proposed