A couple of glitches aside, the U.S. nuclear power plant fleet has been posting very high plant capacity factors for the year to date, according to the federal Energy Information Administration.
From January through June of 2015, the average capacity factor – the ratio of generation produced compared to maximum potential output – was 92.5 percent. This is higher than 2014's impressive 91.7 percent and the 91.1 percent posted in 2010. It is also much higher than the 1970s, 1980s, and 1990s, when the average capacity factors were considerably lower: 54.3 percent, 58 percent and 74 percent, respectively. In the 2000s, the average capacity factor was 89.8 percent.
The improved scores reflect shorter planned outages and fewer unplanned shut downs, reported Power magazine's associate editor Aaron Larson.
The planned outages include refueling and basic maintenance servicing, but they also include uprate outages which involve adapting a plant to a higher output with a new fuel or a higher percentage of new fuel. This can involve considerable modification to plant components, which means longer outages, which means lower capacity factors.
The U.S. fleet has apparently reached a temporary plateau concerning uprates. There were 154 approved uprates as of April 2014, Larson reports. This added 7,035 additional megawatts generated. Uprate outages have declined since then.
In 2014, the fleet set a record low of 59 unplanned reactor shutdowns. However, during the summer season outages were less than 3 percent of the total capacity. That followed a spring refueling and maintenance season in which outages were less than 15 percent of the fleet's total capacity.