Nuclear materials management at Mallinckrodt can be divided into three major sections. These are: (1) maintain the integrity of enrichment, (2) prevent the accumulation of a critical mass, and (3) maintain control over the extremely valuable materials being processed. Since the nuclear power industry has not as yet progressed to the point where definite standards can be set up, each reactor is designed and fueled separately. Thus there are as many core designs as there are designers and each core has its own unique enrichment. The choice of enrichment is a critical part of the reactor design and once the enrichment has been determined there is little or no latitude for changes. After the fuel allocation has been approved, the Commission provides uranium hexafluoride of the desired enrichment. The fuel processor then has the problem of converting the UF& into usable fuel without altering the enrichment in any way. The problem can become quite complicated when several enrichments are being processed simultaneously or in close sequence.