Japan's nuclear power fleet continues to suffer low capacity factors, primarily because of the prolonged shutdown of seven earthquake-affected reactors.
The country's trade association for the nuclear industry, the Japan Atomic Industrial Forum (JAIF), has announced figures showing a weighted average capacity factor of 60% over the period from 1 April 2008 to 31 March 2009.
JAIF said this was the lowest such figure in the last ten years, apart from a 59.7% weighted average in FY2003, when a major program of inspections was launched after a safety scandal.
One factor in the lower level of performance was the extended shutdown of the seven large reactors at Kashiwazaki Kariwa, which was affected by a violent earthquake in July 2007. Nuclear safety was maintained throughout the incident and no-one was hurt at the plant site, but all the units have remained shut down for repairs since the day of the tremors - removing some 7965 MWe from available capacity. However, even excluding these units and three others that have had extended shutdowns, the capacity factor would only rise to 73.0%.
Some 258 billion kWh were generated by Japanese nuclear power plants in FY2008, which was 2.2% down on figures for FY2007. Historically, nuclear power has provided about 30% of Japanese electricity and this is expected to rise to 40% by 2017.
Globally, capacity factors from boiling and pressurized water reactors like those operated in Japan are around the 85% mark. Most reactors operate at around 100% capacity for 12- or 18-month stretches between refuelling, with outages due to unforeseen maintenance jobs or grid issues coming only rarely. One exception is France where the amount of nuclear power on the grid requires some reactors to power up and down with demand.