The Criticality Implications of Taking Credit for Fuel Burn-Up

The first problem usually facing a criticality engineer is data specification. The design engineer and operator need a design and operating ··envelope'' of data which allows practical operation, but the criticality engineer must ensure that key parameters remain within specific limits to maintain criticality safety. Given the high safety standards demanded in the nuclear industry, a naturally cautious view is taken and pessimistic assumptions of parameter values are therefore made. This explains why assessments of spent fuel transport and storage assume unirradiated fissile compositions (the '' fresh fuel'' assumption).