STUDY ON LONG LIFE CORE WITH URANIUM FUEL FOR LSBWR

This paper describes an innovative core concept currently being developed for long operating cycle simplified BWR (LSBWR). LSBWR is a modular, direct cycle, light water cooled, small power reactor. The long cycle operation (15 years) of LSBWR is for the elimination of the fuel pool and the refueling machines and for the capacity usage ratio improvement. We adopt the medium enriched uranium oxide fuels with loose pitched lattice in consideration of the natural circulation for core cooling. To achieve long cycle operation, a combination of enriched gadolinium and 0.7-times sized small bundle with peripheral-positioned gadolinium rod was adopted as a key design concept. A nuclear design for fuel bundle was determined based on three dimensional nuclear and thermal hydraulic calculation. A core performance was evaluated based on this bundle design. Maximum enrichment needed for 15-years operation was estimated below 20wt%. The thermal performance indicated preferable value. Void reactivity coefficient kept negative throughout the operation. The behavior of parameter for the typical abnormal operation transient events was analyzed using computer code. The results showed that the transient performance satisfied the judgment criteria for transient event and was almost the same as the operation plant in Japan.