Shortly after the nuclear disaster at power plants in Fukushima, Japan, the head of the Nuclear Regulatory Commission said that U.S. reactors are safe. Now a Nuclear Regulatory Commission (NRC) task force created in response to the disaster is recommending extensive safety upgrades to deal with problems like the ones seen in Japan, although it also said that nuclear plants pose "no imminent risk."

One of the biggest problems at Fukushima was extended loss of power at the plant that shut down cooling systems, requiring plant operators to take extreme measures such as pumping seawater directly into the reactor, which in turn resulted in the release of radioactive seawater into the environment.

In the U.S., nuclear power plants are typically equipped to operate without grid power for four to eight hours. The new report suggests plants be required to have systems for keeping the reactor and spent fuel pools cooled for at least 72 hours without outside electricity.

The report also recommends updating flood and earthquake assessments after 10 years, rewriting regulations to make them clearer, and conducting training exercises that simulate problems at more than one reactor at a time.

One of the other big issues raised by Fukushima is what to do with spent nuclear fuel, which is currently packed into cooling pools at most nuclear power plants. In Japan, spent fuel in such pools overheated after water escaped. Spent fuel pools can hold more radioactive material than the reactor, and most of the fuel has had a chance to cool off significantly, making it easier to manage than fuel in the reactor.

The task force recommended upgrading the ability to refill these pools at U.S. plants, and the introduction of instrumentation for monitoring them. But it did not recommend that spent fuel be moved more quickly into dry cask storage, which does not require water for cooling, as some experts have advised.

Some experts called for more safety improvements, the Los Angeles Times noted:

The Union of Concerned Scientists, a nuclear watchdog group, issued its own set of recommendations Wednesday that would go much further than the NRC's. It suggested that U.S. nuclear plants be prepared for extreme events. The organization also would require nuclear plants to store more of their spent fuel in dry casks, rather than pools that can overheat in an accident.

It also was critical of the NRC's methodology, noting that it met with industry officials but not outside groups.

"We were somewhat disappointed that the task force did not meet with the public during its deliberations," said David Lochbaum, an official at the union.

Meanwhile, the nuclear industry called for more study before any new rules are implemented. It's worried about the implication of some subtle wording in the report that could lead to much higher costs for nuclear power, according to the The Wall Street Journal:

The panel also proposed essentially setting aside a 1988 rule that has protected the nuclear-power industry against costly upgrades. The industry has used the rule, which requires benefits to public safety to be balanced against industry costs, to beat back regulatory changes it didn't like.

Tony Pietrangelo, chief nuclear officer for the industry's Nuclear Energy Institute, said the proposal to set aside the cost-protection rule amounted to "sweeping change." The NRC "will have to think long and hard," he added, before embarking on such a "major policy shift.". . .

The cost-protection rule was created to shield the nuclear sector after its costs spiraled out of control because of the NRC's reaction to the 1979 accident at the Three Mile Island reactor in Pennsylvania. Billions of dollars of added costs were imposed on the nuclear-power sector, which the industry said stalled its growth for more than two decades.

The cost-protection rule adopted in 1988 has insulated the industry against major upgrades without proof that human health benefits exceeded those costs. In the calculation, a human life was valued at about $3 million. Critics say the rule undervalues human lives, noting that other federal agencies place a value on a human life of between $5 million and $9 million for the purpose of cost-benefit calculations in other areas.

In the days following the disaster at Fukushima, experts believed that getting the situation under control would be a simple matter. The reactor vessels were containing the nuclear fuel, and all that was needed was to pump water into the reactors until power could be restored and the plant's cooling systems restarted. But it has proven much harder to control the situation than expected. Now, TEPCO, the utility in charge of the plant, says that fuel rods in at least one of the reactors melted and made a hole in the reactor vessel. It could take years to construct a containment wall to make up for the hole.

From Reuters:

"There must be a large leak," Junichi Matsumoto, a general manager at the utility [TEPCO] told a news conference.

"The fuel pellets likely melted and fell, and in the process may have damaged...the pressure vessel itself and created a hole," he added. . . .

The finding makes it likely that at one point in the immediate wake of the disaster the 4-meter-high stack of uranium-rich rods at the core of the reactor had been entirely exposed to the air, he said. Boiling water reactors like those at Fukushima rely on water as both a coolant and a barrier to radiation.

U.S. nuclear experts said that the company may have to build a concrete wall around the unit because of the breach, and that this could now take years.

A summary of events at the plant through May 3 can be found here. The International Atomic Energy Agency says that the situation at the plant "remains very serious."

In the United States, meanwhile, a review of nuclear power plants suggest they aren't as safe as regulators had thought. The review, by the Nuclear Regulatory Commission, found problems with equipment installed after the 9/11 attacks to help keep reactors stable in the event of a terrorist attack or a disaster on the scale of the one at Fukushima.

From the New York Times:

Marty Virgilio, the deputy executive director of the agency, told the five commissioners that inspectors checked a sample of equipment at all 104 reactors and found problems at less than a third of them. The problems included pumps that would not start or, if they did, did not put out the required amount of water; equipment that was supposed to be set aside for emergencies but was being used in other parts of the plants; emergency equipment that would be needed in case of flood stored in places that could be flooded; and insufficient diesel on hand to run backup systems . . .

Another problem, staff members acknowledged, is that they have never paid much attention to the issues posed by handling an emergency when there is widespread damage to surrounding roads, power systems and communications links. In the past, the commission has explicitly rejected the notion that it should consider such combined events when reviewing a plant's safety preparations.

And finally... a blue ribbon commission appointed to recommend what should be done with nuclear waste in the United States is meeting today, and is likely to recommend that spent fuel be stored above ground at centralized facilities for decades until a permanent storage facility is built. Spent fuel at the Fukushima plant contributed to radiation leaks there.

A confidential Nuclear Regulatory Commission document obtained by the New York Times details serious threats still facing workers at the severely damaged Fukushima nuclear plant, as well as previously undisclosed details about what has happened at the plant so far. Ordinarily, fuel in a nuclear plant cools to the point that it is easy to manage within several days after the reactor is shut down. But difficulty circulating water and damage to the fuel rods suggest keeping them cool could be a challenge for months.

From the Times story:

Among the new threats that were cited in the assessment, dated March 26, are the mounting stresses placed on the containment structures as they fill with radioactive cooling water, making them more vulnerable to rupture in one of the aftershocks rattling the site after the earthquake and tsunami of March 11. The document also cites the possibility of explosions inside the containment structures due to the release of hydrogen and oxygen from seawater pumped into the reactors, and offers new details on how semimolten fuel rods and salt buildup are impeding the flow of fresh water meant to cool the nuclear cores . . .

Among other problems, the document raises new questions about whether pouring water on nuclear fuel in the absence of functioning cooling systems can be sustained indefinitely. Experts have said the Japanese need to continue to keep the fuel cool for many months until the plant can be stabilized, but there is growing awareness that the risks of pumping water on the fuel present a whole new category of challenges that the nuclear industry is only beginning to comprehend.