Some Considerations in Spent Fuel Pool Fires

This morning, I read the Brookhaven National Labs report Severe Accidents in Spent Fuel Pools in Support of Generic Safety Issue 82 from 1987.  This is an analysis of the risk of large scale radioactivity release from the spent fuel stored onsite in a water pool at a nuclear reactor, in the case that an accident caused a loss of the water in the pool.  This is something that now may have happened (for the first time) in the pool at Fukushima-Daiichi.

The document is long and complex, and there are many very significant uncertainties - to the point where I judge that no-one will be able to reliably predict what may happen in this particular accident.  However, the key points seem to me as follows:

Japan Sliding Towards Worst Case

According to the chair of the US nuclear regulator:

The chairman of the United States Nuclear Regulatory Commission gave a significantly bleaker appraisal of the threat posed by Japan’s nuclear crisis than the Japanese government, saying on Wednesday that the damage at one crippled reactor was much more serious than Japanese officials had acknowledged and advising to Americans to evacuate a wider area around the plant than the perimeter established by Japan.

The announcement marked a new and ominous chapter in the five-day long effort by Japanese engineers to bring four side-by-side reactors under control after their cooling systems were knocked out by an earthquake and tsunami last Friday. But it also created a split between Washington and Tokyo, after American officials concluded that the Japanese warnings were insufficient, and that, deliberately or not, they had understated the potential threat of what is taking place inside the nuclear facility.

Gregory Jaczko, the chairman of the commission, said in Congressional testimony that the commission believed that all the water in the spent fuel pool at the No. 4 reactor of the Fukushima Daiichi Nuclear Power Station had boiled dry, leaving fuel rods stored there exposed and bleeding radiation. As a result, he said, “We believe that radiation levels are extremely high, which could possibly impact the ability to take corrective measures.”

If his analysis is accurate and Japanese workers have been unable to keep the spent fuel at that inoperative reactor properly cooled — it needs to remain covered with water at all times — radiation levels could make it difficult not only to fix the problem at reactor No. 4, but to keep workers at the Daiichi complex from servicing any of the other problem reactors at the plant.

Seems like there is a real potential to have several simultaneous not-fully-contained meltdowns here.

Chernobyl as a Worst Case for Japan