The number of unplanned shutdowns achieved near record levels in 2011, with just 62 across the whole of the US reactor fleet, according to data complied by the World Association of Nuclear Operators (WANO) and the Institute of Nuclear Power Operations (INPO).

“The record-low number of unplanned shutdowns helped America’s nuclear power plants achieve reliability levels on par with the high operational efficiency sustained throughout the past decade,” the US Nuclear Energy Institute said in a statement.

Unplanned shutdowns can result from severe weather or grid disturbances that trigger safety responses. In 2011—despite tornadoes in the Southeast, the Virginia-centered East Coast earthquake, Hurricane Irene and flooding in the Midwest—US nuclear energy facilities posted a capability or availabilty factor of 91.4% percent. The US industry’s record-high capability factor, 92%, was set in 2005.

“Plants with a high unit capability are successful in reducing unplanned outages and completing scheduled work effectively during planning outages,” states INPO’s report on the industry performance indicators.

In addition to the low number of unplanned shutdowns, US reactors also performed well in the areas of safety system performance, industrial safety, and forced capability loss rate.

For the 10th straight year, key backup safety systems concurrently met availability goals more than 93% of the time. The three principal backup safety systems are two main cooling systems and backup power supplies used to respond in the event of unusual situations. Each system at every plant has an availability goal just shy of 100% due to maintenance and testing, and 95% of these backup safety systems met their goal in 2011.

Further the US nuclear facilities demonstrated a low industrial accident rate in 2011 with a record 0.06 industrial accidents per 200,000 worker hours, well below the 2015 goal of 0.1. “Statistics from other industries through 2010, compiled by the U.S. Bureau of Labor Statistics, show that it is safer to work at a nuclear power plant than in the manufacturing sector and even pharmacies and personal care stores, real estate, and financial sectors,” NEI said in a statement.

Finally, in 2011 the median value of 1.4% capability loss remained near historically best levels. Forced capability loss rate measures a plant’s outage time and power reductions that result from unplanned equipment failures, human error or other limiting conditions when the plant is expected to be generating electricity. The 2015 goal for this indicator is a median value of 1%. In the mid-1990s, the median value exceeded 5%, but it has been under 2% each year since 2001 and 1.5% or lower for seven consecutive years.

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