Cycle Length Changes

In the early commercial era (1960s-1970s) of U.S. nuclear power plants, a typical cycle length ranged from 9-12 months. These are relatively short cycle lengths compared to the modern cycle lengths of 18-24 months. In the earlier years, there were many contributing factors to having short cycles. First-generation fuel designs had low achievable fuel burnup, limited uranium enrichment levels, and high uncertainty in fuel performance. Couple that with conservative regulatory philosophy based on limited operational experience and you would expect more frequent outages, inspections, and innovation. The early years tended to error on the side of operability and safety over efficiency and economic operation.

Around the 1980s, operators began to transition towards 18-month cycle lengths. With innovation and significant advancements in research and development, the industry saw improvements in fuel reliability and behavior. Additionally, optimization of reactor core design and loading strategies motivated by reductions in outage frequency and costs began to surface. As fuel enrichment improved and performance improvement initiatives swept across the industry, 18-month cycles became dominant going into the turn of the century.

As both power plant and fuel designs and operational experience continue to evolve, there is increased confidence in 24-month cycle operations. Optimizing plant capacity to meet higher power demands and achieving better economic margins are driving the industry.