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Description
As engineering discussions of the feasibility of new reactor systems, it is necessary to evaluate the impact of the fuels and materials for the neutronics characteristics such as criticality, conversion rate, and fuel balance. It is important to perform the validation of 233Th and 233U nuclear data for a thorium-based nuclear reactor, because those nuclear data contribute significantly to the neutronics characteristics of the reactor.
In this study, in order to perform integral evaluation of 233U nuclear data, measurements of substitution reactivity worth between 233U sample and high enrichment uranium (HU) sample in Kyoto University Critical Assembly (KUCA) were carried out.
In KUCA with solid moderator core, fuel and moderator plates in fuel element were set in a 1.5 mm thickness aluminum sheath and all material plates have nominal cross section of 2” square. In this study, the experimental core was consist of 24 fuel elements and 1 special fuel element. A fuel element was consisted of 31 unit cells and sandwiched by a upper and a lower polyethylene reflector. The unit cell has one enriched uranium (EU) plates of 1/16” thickness, three polyethylene plates of 1/8” thickness. In addition, a special fuel element was loaded in the center of the core. A 233U of HU sample was installed in the central cell of the fuel element (S). The 233U sample was about 9 g U3O8-Al and the HU sample was about 9 g U3O8-Al. The substitution reactivity worth was defined as difference of excess reactivates between 233U or HU inserted core. The excess reactivates were measured by positive period method.
As the experimental results, the substitution reactivity was obtained 0.0146 ± 0.0006 %dk/k. On the other hand, a numerical results by MVP-3 with JENDL-4.0 was 0.0141±0.0006 and the C/E was 0.966 ± 0.041.