Assessing Heat Sink Loss Will Delay Flooding Re-Evaluations, Industry Says

The following news article originally appeared in NEI’s Nuclear Energy Overview.

The NRC’s plan to require licensees to evaluate the potential loss of a nuclear energy facility’s ultimate heat sink, or long-term cooling source, as part of flooding hazard re-evaluations will extend the time needed to complete the work, the industry said last week—a situation the industry believes is unnecessary and inadvisable.

“We do not believe it is prudent to delay the completion of flooding re-evaluations, given the priority attention they merit based on what actually occurred at Fukushima Daiichi,” Anthony Pietrangelo, senior vice president and chief nuclear officer at NEI, said. “The implementation of the flooding re-evaluations based on new information and current methodologies is one of the most important and safety-significant lessons learned from Fukushima.”

Flooding from a tsunami disabled safety systems at the Fukushima Daiichi nuclear energy facility in Japan last year, leading to fuel damage and the release of radiation. In March 2012, the NRC requested updated information on seismic and flooding hazard assessments for all U.S. nuclear energy facilities as part of its response to recommendations from the agency’s post-Fukushima task force. These assessments are among recommendations the NRC staff categorized as Tier 1, or highest priority.

The flooding hazard re-evaluations include the impact on the structures, systems and components that supply cooling from the ultimate heat sink to the reactor, used nuclear fuel pool and containment, Pietrangelo said, but they do not include the loss of the heat sink itself. Adding this element to Tier 1 actions would adversely affect the schedule for completion of the flooding hazard reevaluations for 21 reactors at 13 sites that have downstream dams that hold their ultimate heat sink, he said.

The NRC in 2010 identified dam failure as a potential generic safety issue, based on new information suggesting the possibility of failure was higher than previously thought. An agency review panel recommended assessing flooding from upstream (but not downstream) dam failure as a generic safety issue. The generic issue review panel decided last December to review the effect on the ultimate heat sink of downstream dam failure separately from upstream dam failure “due to the different technical nature of the topic.”

The NRC also decided in March to merge the assessment of upstream dam failure with post-Fukushima actions.

Pietrangelo said the industry is continuing with the re-evaluation of flooding hazards per the current work scope and schedules, which do not include downstream dam failure and the potential loss of the ultimate heat sink.

The industry believes loss of ultimate heat sink should be evaluated as a lower-priority activity. This evaluation would include all potential failure modes, not just flooding, Pietrangelo said. “We look forward to a prompt resolution of this issue so that licensees can continue to move forward with implementing the lessons learned in the most efficient and expeditious manner.”