Studies on Plutonium Burning in the Prototype Fast Breeder Reactor Monju

Studies have been performed on plutonium burning in the Japanese prototype fast breeder reactor Monju. The main aims of these studies were to illustrate the plutonium-burning capabilities of fast reactors and to investigate the consequences of the related core design measures on the main core characteristics of Monju. Burner cores with diluting pins, with diluting subassemblies (also called diluents), and with an internal slice of inert material have been investigated; these require an increased average plutonium enrichment and thus offer an enhanced plutonium-burning rate. On the other hand, the consequences of the elimination of the radial and/or axial blanket have been investigated.

Among the burner concepts, the B₄C containing diluents have been found to be preferable because they cause the smallest maximum linear rating increase and offer the largest flexibility to adapt their reactivity via a modification of the B₄C content. They also do not require a new fuel subassembly concept.

For the case of the blanket elimination, the replacement of the blankets by steel reflectors has been found to be the best solution. The main consequence of the elimination of both blankets is the increase of the maximum linear rating by up to 11%. Whether this increase may lead to problems will depend on the actual linear power level of the core.