Jul 24 6:53 PM

NAS Fukushima report: Accidents will happen

More than three years after the start of the Fukushima crisis, nuclear regulators and industry still lag on implementing upgrades.

If there is one message to take from the National Academy of Sciences report, Lessons Learned From the Fukushima Nuclear Accident for Improving the Safety of U.S. Nuclear Plants, released today, it is that accidents can happen, and it is essential for nuclear plant operators, regulators and public safety responders to all have plans for what to do when one does.

The congressionally mandated report, the result of over two years of work, looked at the responses at Japanese nuclear facilities after the Great East Japan Earthquake and tsunami of 2011, and found the outcomes indicate some obvious actions going forward.

Foremost in both the lengthy report and at the press conference with its authors: Emergency managers, regulators, and most pointedly, nuclear plant operators need to pay better attention to what are called “beyond design basis events” (BDBEs).

The nuclear industry will tell you that its reactors are designed with a degree of redundancy — that there are backup systems, should primary essential safety and monitoring equipment fail. But critics ask a follow up: What if the backup systems fail or are inadequate?

This scenario was very much in evidence at Fukushima Daiichi after the March 11, 2011 earthquake. The plant had backup generators to handle the loss of station power triggered by the quake, but those generators were knocked out by the tsunami. At that point, Fukushima’s crew was left with no obvious disaster mitigation protocol.

The same could be said for emergency responders, who presented with severely damaged infrastructure, had limited access to the plant, limited tools for monitoring external contamination, and no effective plan to evacuate residents both inside and beyond a previously determined quarantine zone.

These “X+1” scenarios have long been the focus of industry watchdogs, and though the NAS will couch their recommendations in terms of better evaluating risk, the strong emphasis in their report makes clear the risk of these BDBEs has not been adequately assessed.

The report’s authors seemed to stress that there exists more and better information on the type of risks to the stability and security of nuclear power plants than is currently considered by operators and regulators. “It is not to say that risks haven’t been considered,” said one of the report’s authors, it is just that the “opportunity exists to expand the breadth and depth of the analysis.”

The light water paradox

Take, again, what happened at Fukushima Daiichi.

The disaster has, at its root, something I’ve previously called “The Light Water Paradox.” As I explained in response to a prior Fukushima study:

Return for a moment to something discussed here last summer, The Light Water Paradox: “In order to safely generate a steady stream of electricity, a light water reactor needs a steady stream of electricity.” As previously noted, this is not some perpetual motion riddle–all but one of Japan’s commercial nuclear reactors and every operating reactor in the United States is of a design that requires water to be actively pumped though the reactor containment in order to keep the radioactive fuel cool enough to prevent a string of catastrophes, from hydrogen explosions and cladding fires, to core meltdowns and melt-throughs.

Most of the multiple calamities to befall Fukushima Daiichi have their roots in the paradox. As many have observed and the latest Japanese report reiterates, the Tohoku earthquake caused breaches in reactor containment and cooling structures, and damaged all of Fukushima’s electrical systems, save the diesel backup generators, which were in turn taken out by the tsunami that followed the quake. Meeting the demands of the paradox — circulating coolant in a contained system — was severely compromised after the quake, and was rendered completely impossible after the tsunami. Given Japan’s seismic history, and the need of any light water reactor for massive amounts of water, Fukushima wouldn’t really have been a surprise even if scientists hadn’t been telling plant operators and Japanese regulators about these very problems for the last two decades.

In the case of Japan, Fukushima operator TEPCO did not account for known seismic and tsunami risks, and, even if they had, they still did not have a plan of action for the total station blackout (known as an SBO) — that X+1 scenario or beyond design basis event.

In the months (and even years) after the beginning of the Fukushima crisis, advocates for American nuclear power commonly downplayed the implications of Japan’s experience, arguing it was a freak “one-two punch.” The NAS report appears to frown on that kind of blinkered assessment. As a case study for U.S. facilities — and the NAS study is meant to inform management of the U.S. nuclear fleet — analysis of the Fukushima disaster says that the earthquake and tsunami were far from unforeseeable, that there were experts that saw it, and that even if that specific chain of events was surprising, the consequences of it should still be considered and prepared for.

Evaluating risk in this more sophisticated (one might even say “honest”) fashion led the NAS panel to make several concrete recommendations — or, as the report tends to phrase things, the panel “recommends particular attention” be paid to “improving the availability, reliability, redundancy, and diversity of specific nuclear plant systems.” Among them, DC backup power for instrumentation and safety systems, tools for monitoring plant status during an SBO, methods for removing heat, depressurizing reactors and venting built up gases, improved heat, hydrogen and radiation monitoring, and better real-time communications.

All are sound conclusions, and ones that have been more or less echoed in previous studies of the crisis, but the gap between saying “attention must be paid” and seeing activity on the part of nuclear regulators and operators still appears wide.

‘100 percent failure’

Case in point: vents.

The GE Mark I Boiling Water Reactor, the design of the damaged reactors at Fukushima Daiichi, and similar Mark IIs, were built with very small containment vessels, making them vulnerable to over-pressurization, and without vents to relieve the pressure in an emergency. This problem was actually recognized by some engineers in the 1970s; still, it took until 1989 for the U.S. Nuclear Regulatory Commission recommended adding the most basic vents to older reactors. (And, even today, one currently operating U.S. reactor — Fitzpatrick in upstate New York — still does not meet those requirements.)

The basic vents were back-fit to the Fukushima reactors prior to the 2011 earthquake.

But well before the 1989 NRC rule, some nuclear watchers, based on observations after the 1979 Three Mile Island accident, suspected the type of vents in the NRC recommendation would not be sufficient in accidents where the nuclear fuel was damaged. So-called “hardened vents,” designed to operate under more adverse conditions, with filtration systems engineered to remove some of the radiation from the released gas, would be necessary to respond quickly and minimize environmental contamination.

There is still some debate on exactly how the vents at Fukushima failed and what role they played in the hydrogen explosions that so severely damaged containment buildings at Daiichi, but there has been little argument that the design modification recommended for all U.S. boiling water reactors failed the test.

The system “demonstrated a 100 percent failure rate for Mark I over-pressurization events,” said Paul Gunter, director of the Reactor Oversight Project at Beyond Nuclear, a nuclear industry watchdog.

The need to retrofit the 23 Mark I and eight Mark II reactors still operating in the U.S. with “sever accident capable” vents and high-capacity filtration systems was a common finding in several post-Fukushima reports. Indeed, just such an upgrade was the firm recommendation of the NRC’s own Japan Lessons Learned Task Force.

But in March 2013, with the Fukushima disaster starting its third year, the Nuclear Regulatory Commission bowed to industry objections, ignored its own task force’s findings and voted 4 to 1 to reject ordering the installation of the robust vents and filtrations systems on the ancient GE reactors.

‘Tragic’ lack of independence

It was an example of “regulatory capture,” said Gunter, which represents the “fundamental problem” with nuclear regulation. “Industry essentially rules the regulators.”

It is a problem the NAS panel seemed to recognize, even if their report failed to recommend any solutions.

“The NRC and industry must maintain a strong safety culture,” said Dr. Emilie Roth, a cognitive psychologist and a member of the NAS Fukushima committee, adding that to do this, “the NRC must maintain its independence.”

When asked if these conclusions were based on any specific examples in either Japan or the U.S., Roth said they were not, but restated the necessity of regulators to represent interests separate from those of the nuclear industry.

It is a sentiment shared by industry watchdogs and good government advocates, but it is not a reality according to Gunther. While he praised the NAS for recommending plant regulations take into account BDBEs, he noted that under the current regulatory regime, “plants are not even in compliance with their design basis, let alone beyond design basis” considerations.

It is fine for the NAS report to recommend enhanced risk analysis, said Gunter, but at present regulators make rules based on a cost-benefit analysis keyed to “industry production costs, not to public health and safety.”

As an example, Gunter returned to the vents. In Japan, reactors now seeking to restart must install state-of-the-art vents and filtration systems. Such equipment has already been installed at the Kashiwazaki Kariwa facility, a demonstration, said Gunther, that the technology already exists.

The incestuous nature of government and industry in Japan is much documented, and regulatory capture was oft cited as a contributing factor to the Fukushima crisis. But even in Japan, its Nuclear Regulatory Agency has been able to require a “lessons learned” upgrade that seems beyond the reach of the U.S. NRC.

The story illustrates in detail the problem the NAS report alludes to by impression: A nuclear industry resistant to learning from the past, uninterested in planning for the future, and virtually impervious to oversight.

“It is tragic in a post-Fukushima world,” said Gunter.


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