Evaluation for the nuclear characteristics of the low U enriched fueled MK-III core

Yoshida, Akihiro ; Aoyama, Takafumi 

The investigation is underway to reduce the U enrichment of Joyo MK-III core fuel. The difficulties of obtaining enriched Uranium and reducing fuel fabrication costs are the items being investigated. In addition, the utilization of weapon-grade Plutonium, of which Pu content exceeds 90%, instead of current reactor-grade Pu, is also under investigation. Initially, specification of the MK-III core fuel was adjusted in order to have the same reactivity worth as the current fuel. The U enrichment were reduced from 18% to 10%, and in some cases as low as 5%. The results are as follows: (1)When Pu content was improved from 30% to 35%, or when weapon-grade Pu was adopted, U enrichment can be decreased lower than 5% for the inner core fuel. (2)To decrease U enrichment lower than 5% for outer core fuel, Pu content must be improved up to 37%. Then deplated Uranium can be adopted for the inner core fuel. When weapon-grade Pu was adopted and Pu content was improved up to 33%, deplated Uranium can be utilized for both inner and outer core fuel. The nuclear characteristics of the low U enriched fueled core were calculated and compared with that of the MK-III standard core (reference corc). The results are as follows: (1)With the increase of Pu and Pu, burn-up reactivity increase. By increasing the substitution reactivity between a spent fuel and fresh fuel subassembly, burn-up reactivity could be compensated. (2)When weapon-grade Pu was adopted, the change of Pu vector per unit burn-up increased when compared with current core fuel. However, the nuclear characteristics were almost the same when compared with the standard core.