On March 11, 2011, the Fukushima Daiichi nuclear power plant on Japan’s east coast was designed to withstand a magnitude-7-plus earthquake. A flood wall 18 feet high stood between the plant and the Pacific. But the Great East Japan earthquake that day measured magnitude 9, unleashing a tsunami that topped 45 feet.

The plant was inundated, backup generators were flooded and fuel supplies were swept away. Tokyo Electric Power Co. (TEPCO) emergency crews soon were without any electric power to run cooling water recirculation pumps to prevent the meltdowns of three reactor cores, explosions from leaking hydrogen, and the second-worst nuclear power accident in history. TEPCO workers, who could not know whether their families were among the 18,500 people killed or missing, had to battle through a horrific crisis they had never prepared for, subsequent investigation found.

The Fukushima tragedy triggered an intense safety review of U.S. reactors by the Nuclear Regulatory Commission and the industry, and a debate that has at times divided the NRC staff from its policymaking commissioners. The industry and its regulator, riveted by the crisis, faced core questions that their Japanese counterparts had not asked in time.

U.S. plants are designed to withstand natural disasters of expected dimensions – a “design basis” threat. Plant operators are also required to prepare for certain “beyond-design-basis” emergencies, such as power outages and large fires or explosions, prompted by the 9/11 attacks. Were the U.S. plants really prepared for such challenges?

And what if a more complex and profound emergency unfolded, a one-two punch such as an earthquake and flooding? What if a once-in-a-millennium, “black swan” catastrophe occurred, like Japan’s magnitude-9 quake? How would defenses and defenders stack up then?

At the NRC’s annual Regulatory Information Conference last week, NRC staff and industry representatives looked back on the five years of response to the Fukushima event and listed an industrywide investment of $4 billion in new equipment, precautions, studies and procedures that they agreed made the U.S. plants more secure.

“We’ve worked very hard implementing lessons learned from Fukushima,” said Jack Davis, director of the NRC’s Japan Lessons Learned Division. “We’ve made substantial progress. There are real, tangible safety enhancements that have been made out there.

“Today, U.S. plants are definitely much better prepared to deal with extreme natural hazards and other beyond-design-basis events,” he added.

FLEX response

The most important of these enhancements has been the NRC-mandated creation of two new flexible emergency response “FLEX” centers, in Memphis, Tenn., and near Phoenix, where spare portable generators, water pumps, hoses and other emergency equipment are stored and maintained. Those supplies are ready to be deployed in 24 hours or less, using heavy-lift helicopters if necessary, to maintain cooling capability for reactors and spent fuel pools if plant power is lost.

Anthony Pietrangelo, the Nuclear Energy Institute’s vice president and chief nuclear officer, noted that hose and power connections for emergency equipment have been standardized across the industry. “In addition to the national response centers, all emergency equipment used across 60 sites in the country are interchangeable, so it’s like you have 62 response centers. We’ve simplified the connections on these,” he said in an interview. “Basically, they are all plug and play.” Emergency equipment is more tightly protected now, as well.

The changes give plant operators new capability to handle potential emergencies, including those that can’t be predicted, conference speakers said.

At last week’s conference, Edwin Lyman, a senior scientist at the Union of Concerned Scientists and a persistent critic of industry and NRC safety actions, faulted the commission’s response to Fukushima as incomplete and confusing. The FLEX equipment must be subject to NRC rules and inspections, he said.

“UCS certainly acknowledges there has been an enormous effort on the part of the NRC and the industry to address the safety vulnerabilities after Fukushima,” Lyman said. “We thank everyone for all that work that has been done, but we’re just not sure it’s good enough.”

In addition to volumes of mandatory regulations, nuclear plant safety is addressed by voluntary, industry-developed severe accident management guidelines (SAMGs) that deal with accidents beyond anticipated design-basis threats.

Inconsistent remedies

Immediately after the Fukushima accident began, the NRC ordered inspections of every U.S. reactor to check on emergency preparedness. The inspections revealed a sizable list of shortcomings, involving both regulated design-basis threats and emergencies covered by voluntary guidelines.

A valve that operated a water main needed for fire response at the Millstone plant in Waterford, Conn., would be underwater in a design basis flood. At the Brunswick reactor in Southport, N.C., fire pumps were located in a building that was not protected against earthquake damage. A fire pumper truck at the Callaway plant near Fulton, Mo., did not have a suction hose long enough to reach water supply sources. Operators at the Wolf Creek nuclear plant in Burlington, Kan., couldn’t find some emergency equipment and had to locate it in a computer database – which would not have run if the plant lost electric power.

The issues found in the post-Fukushima inspections were promptly remedied, the NRC said, but the inspection results indicated that “worst case” thinking wasn’t the rule in all the plants before the Fukushima disaster. The NRC inspectors who found inconsistent implementation of SAMGs attributed it to the guidelines’ voluntary nature.

The starting point for the NRC’s Fukushima review was a report by senior NRC staff members called the Near-Term Task Force, delivered four months after the accident, which urged that the voluntary guidelines be made into requirements. In opposing such a move, the NEI said the NRC’s “regulatory cost-benefit evaluations indicate this is not justifiable using quantitative measures.” The commission sided with the industry on the issue.

At the conference, Davis said he had heard “from many stakeholders and even some NRC staff” that “where we are today … is significantly different from what the Near Term Task Force originally envisioned or had recommended.”

“Some view this as perhaps watering down or chipping away at what the original recommendations were. In reality, it was learning and then focusing on what really matters for safety,” he said.

The commission has backed up the task force’s concern that the design basis threats to U.S. reactors were calculated in inconsistent and potentially inadequate ways. The task force said that in some nuclear plants, the design basis does not consider the probable maximum flood. In other cases, the maximum flood is calculated differently for different units at the same plant. Some plants are overly reliant on stopgap measures to deal with extreme emergencies, such as the use of unstable sandbags to raise levels of flooding protection.

“The Task Force has concluded that flooding risks are of concern due to a ‘cliff-edge’ effect, in that the safety consequences of a flooding event may increase sharply with a small increase in the flooding level.”

The NRC responded by ordering new studies of flooding and earthquake hazards, and implications for U.S. reactors.

What took so long?

Several speakers at last week’s conference took up the question of why it took the tragic failures of planning and analysis that were at revealed in the Fukushima Daiichi disaster to prompt a deep look at U.S. reactor safety.

“We struggled early on to think beyond design basis, because we’ve all grown up with design basis and that’s been our focus,” said Scot Greenlee, senior vice president for Exelon Nuclear Generation. It put guardrails around the issue. “We have learned that we have to have our plants designed and capable of dealing with things outside that design basis.”

“I think that is where the safety culture has changed,” he added.

New threat profiles will be completed to reflect the most recent evidence for seismic and flooding hazards – a step Japan never took.

Davis concluded, “There is still a sizable amount of work that still needs to be completed.” History will have to reveal whether the new threat profiles got it right.