The following story originally appeared in NEI’s Nuclear Energy Overview.
One year after the Fukushima Daiichi accident in Japan, the U.S. nuclear energy industry has begun acquiring additional safety equipment as part of a “diverse and flexible” response strategy that is generally aligned with the U.S. Nuclear Regulatory Commission’s near-term priorities, industry executives told about two dozen reporters at a press conference this week in Washington, D.C. While the industry and the NRC agree that America’s nuclear energy facilities are safe, making them safer based on lessons from Fukushima is a high priority.
“Time is of the essence,” said Chip Pardee, chief operating officer for Exelon Generation and chairman of the industry’s Fukushima Response Steering Committee. “We are well-prepared for extreme natural disasters,” he said, “but simply concluding that if it happened here we would be well-prepared is not an adequate response.” The industry intends to complete safety enhancements within the five-year time frame established by the NRC, Pardee said. To that end, “we are proceeding informed by what the NRC is doing, but [we are] out in front of regulations,” he added.
The NRC is expected shortly to issue three orders and three requests for information, which were made available in draft form last month. The orders address mitigation capability for beyond-design-basis events, reliable hardened vents for Mark I and II containments, and additional instrumentation for used fuel pool monitoring. The information requests focus on the re-evaluation of seismic and flooding hazards, communications and staffing during multi-unit events.
The industry determined that a symptom-based approach is the best way to ensure continued safety, given the range of extreme events that potentially could affect a nuclear energy facility.
Pardee said the industry “concluded that our defenses would best be improved by going to the end state that occurred in Japan—that is, loss of all AC electrical power and loss of heat sink. There were no systems functioning that would allow those nuclear power plants to reject the heat that was continuing to be generated.” It was the loss of these functions that led to the Fukushima accident. Rather than focusing on the cause of an event, the industry’s approach is to focus on the symptoms.
Pardee likened this approach to the decision-making process followed by medical professionals treating patients in a hospital emergency room. Rather than diagnose the ailment, they seek first to stabilize the patient, Pardee said.
“We said never mind how we got there, never mind debating how likely it could be or how extreme it could be,” Pardee said. “We’re going to assume that our plants will lose AC electrical power [and the] ability to reject heat through any of our normal systems or emergency systems.” The question is what to do in that situation.
This line of thinking led to the development of an approach called “FLEX,” which addresses major challenges such as the loss of power to maintain effective reactor cooling, as was encountered at Fukushima after the massive tsunami swept over the facility and damaged three of the facility’s six reactors.
FLEX is intended to provide an additional layer of defense-in-depth for beyond-design-basis events. This all-hazards approach uses backup portable equipment to prevent fuel damage and preserve containment integrity if a plant loses off-site electrical power and heat-removal capability. The response strategy calls for positioning additional portable generators, pumps and other backup equipment at strategic locations on site and in regional depots. The additional equipment builds on the substantial safety enhancements made after the terrorist attacks of Sept. 11, 2001.
“We think we can provide basically an indefinite supply of AC power such that you preclude core damage,” said NEI Senior Vice President and Chief Nuclear Officer Anthony Pietrangelo. “FLEX is totally focused on preventing core damage.”
The industry last month unanimously committed to order the first phase of portable on-site equipment by March 31. Some companies already have started to procure additional contingency equipment, including large portable generators, diesel-driven pumps, small-load diesel generators, fire trucks and portable ventilation units.
Pietrangelo said the industry is developing guidance on how to implement FLEX, the keystone of the industry’s response to Fukushima. Additional guidance will focus on the detailed reviews, or walkdowns, conducted throughout a plant to assess seismic and flooding protection as well as communication and staffing for multi-unit events, hardened vents and additional monitoring for used fuel pools.
“We have task forces working on each of these topics,” Pietrangelo said, in advance of the NRC orders and requests for information. “We think we’ll be able to move through all this work in a very quick manner—within five years. That’s the commission’s expectation.”