14.6. The operating cycle length is the planned operating time before shutdown for refueling is required. It is an important fuel reload design parameter and sometimes is expressed in units of fuel burnup. For many years, operating cycles of 12 months were common. However, in recent years, longer cycles became economical as the cost of uranium and en­richment remained relatively low and the advantages of a higher capacity factor became more significant. Also, longer cycles offer more flexibility for generation management.

14.7. Generation management is important for a utility having several nuclear units so that overlapping refueling and maintenance shutdown periods will be avoided. Such outage periods are normally 1 to 2 months long. Also, less frequent refueling has the advantage of reduced radiation exposure to operating personnel. Therefore, many utilities have adopted operating cycles of 18 months and in some cases as long as 24 months [1]. The increase in permissible core peaking factors as a result of changes in 10 CFR 50 Appendix К tends to simplify reload core design for extended cycles.

14.8. Outage management requires long-range strategic planning to maximize plant availability by making the most efficient use of the time available for plant maintenance. For example, project priorities, many to meet NRC requirements, are generally established years in advance, with individual projects scheduled over a series of outages, as appropriate [2].