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U.S. Nuclear Plants Not Fully Equipped to Handle Extreme Events

After studying the Fukushima disaster, a Nuclear Regulatory Commission task force recommends a dozen changes to U.S. reactors



Nuclear Regulatory Commission

U.S. nuclear plants should be hardened to better withstand earthquakes and other extreme emergencies that could lead to a radioactive release, the Nuclear Regulatory Commission's Japan Task Force has recommended.

The task force's 90-page report on the implications of Japan's nuclear disaster said that an accident involving damage to reactor cores and uncontrolled escape of radioactivity was "inherently unacceptable." It called for a dozen actions to improve plant safety and redefine NRC regulations governing severe emergencies. The report was delivered to commission members and key congressional committees yesterday and will be released to the public today.

"Continued operation and continued licensing activities do not pose an imminent risk to public health and safety," the task force of NRC experts said. "However, the Task Force also concludes that a more balanced application of the Commission's defense-in-depth philosophy using risk insights would provide an enhanced regulatory framework that is logical, systematic, coherent and better understood," according to a summary released by the NRC last night.

The dozen recommendations include:

  • Requiring that equipment and procedures are in place to keep reactor cores and spent fuel pools cool for at least 72 hours after an emergency, and that backup power is available to run cooling systems for at least eight hours if power from the outside grid or emergency generators is lost in a "station blackout" emergency. Some U.S. plants have a four-hour backup power capability. The 72-hour requirement would be new.
  • Requiring that emergency plans address accidents involving multiple reactors on the same site. Current regulations generally center on single-reactor emergencies.
  • Adding seismically protected systems and instrumentation to assure continued cooling of spent fuel pools, including at least one source of electric power that can operate cooling pumps and instruments at all times.
  • Requiring hardened vent designs for Mark I and Mark II reactors, the models at Japan's Fukushima Daiichi reactor complex where three units suffered explosions tentatively blamed on hydrogen that leaked from vent systems.
  • Strengthening regulatory oversight of plant safety "by focusing more attention on defense-in-depth requirements."

The Japan task force headed by NRC veteran Charles Miller will meet with NRC commissioners July 19 to review the report, and will hold a public meeting on its recommendations July 28.

More extensive review still to come
It is not clear whether the commission will initiate regulatory changes on the basis of the task force recommendations, or will wait until a second and more extensive review of the Japanese accident is completed at the end of this year.

But initial reactions to the report indicated it may be pulled into the ongoing political debate over nuclear power and NRC regulation.

Rep. Ed Markey, (D-Mass), a senior Democrat on the House Energy and Commerce Committee, said the commission should quickly to adopt the task force recommendations, saying "America's nuclear fleet remains vulnerable to a similar disaster."

Sen. James Inhofe, (R-Okla.), top Republican on the Senate environment committee, disagreed. "Changes in our system may be necessary," Inhofe said, but "a nuclear accident in Japan should not automatically be viewed as an indictment of U.S. institutional structures and nuclear safety requirements," the Associated Press reported.

"A 90-day review does not permit a complete picture of the still-emerging situation," said Steve Kerekes, a spokesman for the Nuclear Energy Institute. "Therefore, we strongly recommend that the NRC seek additional information from Japan that would help establish the bases for actions."

Last month, Japanese authorities released an initial investigative report on the causes and consequences of the March 11 earthquake and tsunami disaster at Fukushima Daiichi that documented weaknesses in planning for extreme emergencies and anticipating severe damage to multiple reactors at the site, and chaotic conditions confronting operators as because of equipment and instrumentation failures.

Following the emergency, the NRC ordered inspections of emergency preparedness at the 104 U.S. reactors. While the results did not reveal imminent threats to reactor safety, the commission said, the inspections documented gaps in emergency planning and cases where emergency equipment might not withstand earthquakes or other severe events.

Miscellaneous risks
For example, the NRC reported that the Diablo Canyon nuclear power plant on southern California's coast had a single diesel-driven pump to provide emergency cooling water to a single reactor in case an earthquake cut off normal water flow. The pump could not have serviced both of the plant's reactors if they lost normal water supply simultaneously, the NRC staff said.

The plant's six emergency diesel generators were located in the same plant area, and thus vulnerable to a "common mode" failure. An earthquake could cause a structural failure in the building where the fire truck is stored, and debris could block crews from using the truck.

Entergy's Arkansas Nuclear One plant safety plan was directed against the loss of offsite power to one of its units, and did not anticipate a simultaneous additional threat such as an earthquake.

At Duke Energy's Oconee Nuclear Station in South Carolina, pumps required to remove water from auxiliary buildings in a flood could not be used because the plugs did not fit any outlets in the area. Instrumentation on spent fuel pools would be unavailable if power were lost, which would require workers to visually inspect water levels -- "an unacceptable requirement under some scenarios," the NRC said. One such scenario would be a loss of water in the pool to a level that permitted fuel rods to ignite and release perilously high radiation levels.

The NRC said that all issues have been fixed or put on schedule for correction, and that the safety of the reactors was not compromised.

The task force recommendations included proposals to strengthen and standardized plant defense in response to the inspection findings.

The task force also called for a more "coherent" approach to reactor safety issues to improve what it called a "patchwork of regulatory requirements and other safety initiatives."

The NRC's review of the Japanese accident has centered on a key distinction in NRC regulations that cover "design basis" or anticipated accidents, and "beyond design basis" threats from extreme disasters that are considered less likely but are potentially more dangerous. "I am really bothered by this separation between design basis and beyond-design basis," NRC Commissioner George Apostolakis said at a commission meeting in May.

"I appreciate the need for a design basis. Licensees know what they have to do. We impose all sorts of conditions. This particular pump must deliver this flow rate under these conditions. And then we are going to inspect. We asking them to test it and tell us what they find, all that."

The plant owners' responses to beyond design basis threats are usually voluntary. "We keep saying, 'Oh, these are beyond basis events therefore we don't' get involved.' We are happy that the industry responded. We look at it once. That's it. In the future it's up to them. I am really bothered by that," Apostolakis said.

"It is a constant challenge we have to deal with," NRC director of operations Bill Borchardt responded. "There is a balance."

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500

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