Fukushima: The Salt Problem

Posted by Eben Harrell Thursday, March 24, 2011 at 3:09 pm

Chernobyl, Fukushima, meltdown, Salt

It's worth remembering, as the battle to prevent a massive radioactive release at the Fukushima power plant approaches the end of its second week, what a best-case scenario might now look like. In the best-case, emergency crews will restore cooling to the reactor cores and spent fuel pools and thus prevent the further release of radiation. What will then follow is a hugely expensive clean-up operation of the surrounding area and an (even more) expensive decommissioning of the plant itself. Decommissioning of nuclear power plants, even ones that haven't suffered serious accidents, is an eerie business; the plant is gutted until all that remains is an abandoned, radioactive hulk that is locked up for hundreds of years before it can be dismantled. That, at this point, would be a dream outcome at Fukushima.

Before then, emergency crews face a number of obstacles that many experts believe will take weeks to resolve. Workers must drain radioactive water that has come into contact with damaged reactor cores and they must find a safe way to release radioactive gas. As they do so, they face multiple problems, including one that has only recently come to the attention of outside experts: the build-up of salt in the reactors.

The salt, which has accumulated from the seawater that emergency crews have used as a last-ditch method to cool the reactors, might cause the reactors to overheat and possibly even meltdown. As seawater evaporates, salt scaling could insulate the reactor fuel and impede heat transfer and thus cooling. In a worst case, as the rods heat up, their zirconium cladding could rupture, and gaseous radioactive iodine inside could leak out; the uranium core itself could even melt. This, of course, would release event more radioactive material.

The New York Times, citing a former engineer with General Electric, which designed the reactors at Fukushima, estimates that 57,000 pounds of salt have accumulated in Reactor No. 1 and 99,000 pounds in Reactors No. 2 and 3. But those reactors are larger. And Shan Nair, a British nuclear safety expert who was part of a panel that advised the European Commission on its response to the Chernobyl disaster in 1986, told Ecocentric that it's very difficult to know the danger posed by salt accumulation without more information. "Simply the amount of salt is not the only factor. The salt will melt, some of it will be burned off in vapor. Determining the safe level is like the sort of question you'd ask a PhD student applying for a job in the nuclear industry. Without more information, however, I can already tell you, roughly, it would take a hell of a lot of salt to cause a problem. I'm not concerned about it."

Not all nuclear experts share Dr Nair's sang froid. Some even worry that the Fukushima crisis will get worse before it gets better. The Union of Concerned Scientists (UCS)--not known for taking alarmist positions—criticized the Japanese government yesterday for not extending the evacuation zone around the site, which is currently set at a 12-mile radius. The U.S. Nuclear Regulatory Commission has advised US citizens within a 50 mile radius around the site to evacuate, but Japan has not extended the zone. In a editorial on the UCS's blog, the UCS's Ed Lyman said: "The crisis is not over. Given the uncertainty over future releases, we believe Japan should extend that evacuation zone."

For his part, Dr. Nair is more optimistic. He says the crisis has already shifted to a clean-up operation. "The key was getting power restored to the pumps. Until then they were in a dicey situation. But now they have brought power back to the facility I am not concerned.

"The challenge is now dealing with the clean-up and taking action to avoid contamination of foodstuff. It sounds terrible that some of the radioactive releases have been taken up by crops—but it's simply a question of throwing away those crops. It's a short term contamination event that will create bad publicity and a very expensive clean-up but in terms of public health the problem is very manageable."

Indeed, health experts on Thursday reported that--barring any further release of radioactivity or unforeseen events—the health effects of the Fukushima crisis should remain minimal. As for a panic in Tokyo following the discovery of Iodine 131 in the tap water, Mary Helen Barcellos-Hoff, the Director of Radiation Biology in the Department of Radiation Oncology at NYU Langone Medical Center, told Ecocentric that it should not be cause for concern. "The risk is when there is chronic exposure--that happened in Chernobyl as people ate contaminated food over a course of months. These levels in Tokyo are already very low and they were transient."

But that's not to say that Fukushima has not already proven to be a massive nuclear accident. Indeed, Reuters cited an Australian expert on Wednesday who claimed that the release of two types of radioactive particles in the first 3-4 days of the nuclear crisis is estimated to have reached 20-50 percent of the amounts from Chernobyl in 10 days. That followed an estimation from France's IRSN radiation protection and nuclear safety institute that leaks represented about 10 percent of those from Chernobyl.

Health experts were quick to point out several crucial differences, however.

"At Chernobyl, the population was not generally aware that the accident had happened," Malcolm Crick, Secretary of the U.N. Scientific Committee on the Effects of Atomic Radiation, told Reuters. "People in the nearby town of Pripyat were watching the fire from just a kilometer or so away. They were evacuated a day or so later. In Japan, there was a precautionary evacuation early on."

What's more and perhaps most crucially, wind blew Chernobyl's radioactive cloud over population and land; the prevailing breeze in Fukushima has dispersed most of the radioactivity over the Pacific.

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