Nearly all of the events that occurred at Japan’s Fukushima Daiichi nuclear energy facility following the massive March 11 earthquake and tsunami can be traced to the complete loss of electricity, including backup generators and emergency batteries, that was needed to power reactor cooling systems.
In response to the Fukushima accident, the U.S. Nuclear Regulatory Commission (NRC) is re-evaluating the agency’s “station blackout” requirements for dealing with power outages. U.S. nuclear plants are required to have a minimum of four hours of emergency power; many plants exceed that requirement. That’s in addition to the several locomotive-sized diesel generators that provide layer upon layer of backup power for systems to safely shut down and maintain a reactor should electricity from the grid be disturbed.
The nuclear energy industry agrees with the NRC that the issue should be re-examined and that pre-staging backup power sources is important for the continued safe and reliable operation of nuclear power plants after an extreme event.
Within days of the Fukushima Daiichi accident, every electric utility that operates a nuclear plant in America began a series of detailed inspections to validate safety and emergency response systems, personnel resources and programs. Companies continue to assess each facility’s ability to maintain safety systems and protect reactors even if a plant loses all electric power. Some companies already are adding equipment that will provide additional means of powering the systems that maintain core and fuel pool cooling, in the rare event that multiple layers of backup power sources fail.
U.S. nuclear power plants have demonstrated their ability to maintain plant safety systems even when they’ve separated from the power grid for extended periods of time. For example:
- In 1992, nuclear power plants in Florida withstood power blackouts related to Hurricane Andrew. The Turkey Point nuclear plant operated on emergency power from on-site diesel generators for nearly six and a half days.
- In 2003, a widespread loss of electricity throughout the Northeast and Midwest disrupted off-site power at nine nuclear power plants. All maintained backup power and operated without incident.
- In 2005, Hurricane Katrina struck southern Louisiana and disrupted off-site power at the Waterford nuclear plant. The plant remained safe while using emergency diesel generators for four and a half days.
- In April of this year, a tornado damaged the electrical switchyard at the Surry nuclear plant in Virginia, resulting in a loss of off-site power. Emergency diesel generators powered reactor safety systems, until off-site power was restored two days later.
Although the recommendation by the NRC’s Fukushima Daiichi task force that plants be required to have at least eight hours of emergency power might be appropriate for some nuclear energy facilities, it would be unnecessary for plants that have a low risk of a power outage and readily available alternative power supply options.
With on-site and off-site emergency response equipment, resources and strategies, U.S. nuclear plants will ensure containment integrity, core cooling and fuel pool cooling functions to prevent fuel damage from occurring. Application of the lessons learned from the Fukushima event will allow U.S. nuclear plants to maintain electrical power continuity so that all reactors are safe with cooling systems functioning after any extreme event.