The following news article originally appeared in NEI’s Nuclear Energy Overview.
The study considered ways to prevent the release of radioactive materials following an accident in which loss of core cooling capability results in fuel damage and challenges containment integrity.
After such an accident, operators can cool the reactor, reduce containment pressure and retain radioactive materials by using water-spraying systems, immersing the core, and venting. EPRI’s analysis found that combining these strategies is more effective than individual measures.
In particular, the report says that combining containment sprays or immersion of damaged fuel with a specifically-designed vent that can reliably open and close at appropriate times would provide a more than 1,000-fold reduction in the amount of fission products released. The water would both cool the damaged fuel and absorb nuclear fission products.
The report urges additional analysis to more fully integrate controlled venting with plant emergency procedures.
Adding low-efficiency filters to vents can further reduce the release of radioactive materials, the report says, and recommends research to evaluate the efficacy of filter designs.
The report acknowledges the rarity of severe accidents such as occurred at Fukushima Daiichi. Based on the NRC’s nuclear plant safety goals, less than 0.01 percent of accident scenarios would result in fuel damage.
EPRI’s report also observes that “the best way to avoid radiological release and potential land contamination is to prevent an accident from occurring by improving and augmenting the strategies for preventing core damage.”
The U.S. nuclear energy industry is enhancing its capability to deal with extreme events such as long-term station blackout, in which the normal ability to spray or flood containment may not be available, by providing alternative mechanisms to supply water.
Applying lessons learned from the Fukushima accident, U.S. nuclear energy facilities are implementing a diverse and flexible, or FLEX, response strategy. To address the loss of cooling capability and off-site electric power, nuclear power plants are adding additional portable equipment like backup generators, pumps, hoses, fittings, satellite communications gear and more to provide another layer of safety. FLEX also includes positioning backup equipment at off-site locations, including regional response centers and other nuclear energy facilities.
“Prevention is the best protection when it comes to reactor fuel damage. We have built America’s nuclear energy facilities with a combination of permanent and portable safety systems,” said Steven Kraft, NEI’s senior director for Fukushima response coordination and strategy.
Kraft added, “We also are investigating additional measures to protect public safety and the environment, including providing a water flow that would quickly cover any damaged fuel, using existing or enhanced systems to provide cooling water spray or flooding inside the reactor containment building, and utilizing venting systems for the containment building should operators need to release the buildup of pressure and gases.”