[en] The use of burnup credit in the criticality design of spent fuel shipment casks and spent fuel storage pools has been discussed for a long time. In the safety design of the Rokkasho Reprocessing Plant, the use of burnup credit for the spent fuel storage was officially approved in Japan, after a long discussion among specialists of nuclear criticality safety. In the past design of nuclear criticality safety, fresh fuel was assumed, while the effects of fuel burnup were ignored. In this paper, the use of burnup credit in the design of spent fuel transport casks and spent fuel storage pools is discussed. (author)