May 14, 2011

US nuclear plant safety and waste disposal

Despite repeated assurances that American nuclear plants are better equipped to deal with natural disasters than their counterparts in Japan, regulators said Thursday that recent inspections had found serious problems with some emergency equipment that would have made it unusable in an accident.

In addition, the staff of the Nuclear Regulatory Commission acknowledged that the agency's current regulations and disaster plans did not give enough consideration to two factors that had greatly contributed to the continuing Fukushima Daiichi crisis in Japan: simultaneous problems at more than one reactor and a natural disaster that disrupts roads, electricity and other infrastructure surrounding a plant.
The briefing was part of a review requested by the commissioners to evaluate the vulnerability of American reactors to severe natural disasters like the ones that hit the Japanese plant in March.
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.
he N.R.C. now looks at how well a plant's design can handle a problem at just one reactor, even if there is more than one reactor at the site.
"You have to take a step back and consider what would happen if you had multiple units affected by some 'beyond design basis' events," Mr. Miller said.
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.
Simultaneous with the commission's meeting, Representative Edward J. Markey, a Massachusetts Democrat, released a report arguing that a variety of other shortcomings existed at nuclear plants, including the frequent failure of emergency diesel generators, which are essential to plant safety if the power grid goes down. He also criticized the commission for not requiring plants to have a backup power source for spent fuel pools while the reactor is shut for maintenance or refueling.
The Fukushima accident has cast new attention on spent fuel pools; the reason the United States government recommended that Americans stay 50 miles from the plant was damage to the spent fuel pool of Fukushima's Unit 4, a reactor that was shut down before the March 11 earthquake and tsunami.
Mr. Markey pointed out that in the last eight years, the commission had received 69 reports of inoperable diesel generators at 33 plants, with six of those generators out for more than a month. The diesels provide power for water pumps that allow removal of "decay heat," the heat that fuel generates even after a reactor shuts down. The Fukushima plants shut down successfully but decay heat wrecked their cores.
Mr. Markey also complained that the commission had allowed some plant operators to remove equipment that eliminates hydrogen produced by overheating fuel. In addition, there is no requirement for equipment to remove hydrogen in the rooms where spent fuel is stored; the building surrounding Fukushima Unit 4 was destroyed by the explosion of hydrogen that came from the spent fuel pool.
Commission officials said they were reviewing their previous decision to permit very heavy loading of the spent fuel pools. Thinning them out would reduce the amount of heat production that had to be dealt with in case of a severe accident, they said.
Waste Disposal
A commission created to help resolve the impasse over the disposal of the nation's nuclear waste will propose establishing one or more sites where used reactor fuel could be stored in steel and concrete structures above ground on the earth's surface for decades, members of the commission said this week.
A draft recommendation for such sites is to be discussed on Friday at a meeting of the panel, which was set up last year by the Department of Energy after President Obama canceled a longstanding plan to bury waste atYucca Mountain, a site in the Nevada desert.
The commission will also recommend opening a new effort to find a burial site, members said, and suggest that it be led by an organization that is independent of the Department of Energy, which has been working on the waste disposal effort for decades. 
The quest for a national repository for spent fuel has been a festering issue for decades but gained higher visibility after a March 11 earthquake and tsunami hit the Fukushima nuclear plant in Japan. The disaster not only damaged reactors but led to the loss of cooling water in at least one pool of spent radioactive fuel, raising the risk of the release of radioactive materials.
At nuclear plants in the United States, pools of spent fuel are far more heavily loaded. The National Academy of Sciences warned in a study in 2005 that the presence of vast stores of radioactive fuel could make the plants an attractive target for terrorists.
For now, members of the waste commission say, the panel is unlikely to make a recommendation for starting work on two controversial disposal methods: reprocessing the spent fuel to recover plutonium for reuse, as France and Japan do, or building a new class of reactors that would break up the most troublesome wastes into materials that are easier to handle. Instead, it will recommend more research, the members said. "Neither the technology nor the economics are ready to compel us to make a decision on that at this point," said Phillip A. Sharp, an Indiana Democrat on the commission.
The 2005 study by the National Academy of Sciences, ordered by Congress after the attacks of Sept. 11, 2001, made a variety of recommendations for nuclear waste disposal, some of which were kept secret. One obvious approach has been moving the fuel into dry casks, or steel and concrete structures in which the fuel is cooled by the natural circulation of air rather than any moving parts. Such casks are already in use at a variety of reactor sites.
The commission will recommended that storage of such casks be centralized at a handful of sites, starting with "orphan" sites where the reactors have been retired and torn down. The number of orphaned nuclear sites will grow significantly before the United States can establish a permanent burial place, commission members predict.

Read more here and here

Post a Comment