Give Us Our Daily Strontium Dose …
The damaged Fukushima nuclear plant fails to vacate the headlines. The latest revelation was that one of the rickety water tanks that were hastily erected to hold some of the contaminated water accumulating in the plant has apparently begun to leak. Radiation in the vicinity has spiked to 18 times the previous measurement, a level so high that it would reportedly kill a man exposed to it within four hours (meanwhile, even higher levels of radiation were measured).
When we last wrote about the plant, we didn't mention a problem that appears to be even more daunting than the contaminated water issue.
There are altogether 1,331 spent fuel rod assemblies stored on the top floor of the most heavily damaged reactor number 4. Each one of them weighs about 300 kg (660 lbs.) and they will have to be removed manually – underwater.
This is a huge challenge because workers won't be able to remain near the spent fuel very long: the radiation is simply too high. 550 of the assemblies had been removed from the reactor core just before the tsunami struck and are still extremely hot. The rods contain the radiation equivalent of 14,000 Hiroshima bombs (embodied in cesium 137 and strontium 90 with a half-life of about 30 years each, and plutonium 239 with a half-life of 24,000 years; presumably they also contain traces of technetium 99 and iodine 129). Therefore, work crews won't have a chance to develop routines. As soon as a crew is working well together, it will be replaced. According to the Asia-Pacific Journal:
“The assemblies are to be removed from a concrete fuel pool 10 meters by 12 meters in area, and from within water 7 meters deep. The structure’s base is 18 meters above ground level. Removing fuel assemblies is delicate enough at the best of times, but the pool itself may have been “damaged by the quake, the explosion or corrosion from salt water that was poured into the pool when fresh supplies ran out during the crisis.”
The entire reactor building is tilted and the cranes and related equipment that were previously used to move fuel rod assemblies by computer control were destroyed. The building has been propped up, but both it and the equipment inside have probably been corroded further by salt water. TEPCO originally planned for two years to remove the fuel rods and has now reduced the schedule to one year, but that seems rather overoptimistic.
The fact that the work crews won't have opportunity to develop good routines and learn to work together is a big problem because no mistake must happen. Just because fuel rods are spent does not mean they cannot go critical – they most definitely can. All it takes for that to happen is for two assemblies to get too close together. Dropping one of the things during the removal process is a strict no-no. If the spent fuel assembly does go critical – and note, another earth quake might do the trick as well – there will be no way to stop the chain reaction, since there are no cooling rods in a spent fuel tank. In that event a very large populated are would be affected and would likely have to be evacuated.
An Impossible Task?
In the meantime, Japan's government has reluctantly increased its involvement in the clean-up. Why the reluctance? Apparently it is seen as a political risk for prime minister Abe. As long as TEPCO is in charge, all mistakes and problems that crop up can be blamed on it. Once the government takes over, any future missteps will become its babies. In our previous update on the situation we wrote:
“The government may be able to marshal more resources, but the complexity of the task will remain exactly the same. It is beginning to look possible that the situation cannot be brought under control at all, regardless of which agency takes control of the clean-up process. It may well be that it is simply beyond current technical capabilities.”
There are two factors imposing limits on what can be done: technological capabilities and capital. The latter may not be a big problem for Japan, but we have just received official confirmation that our initial speculation about the difficulties posed by the task was apparently quite correct:
“The government has insisted that the utility should be responsible for the cost of decommissioning the reactors, a job expected to take decades and require as yet non-existent technologies, although the government has budgeted research and development funds – including an industry ministry request for a 40 percent boost to 12.5 billion yen in the budget for 2013/14.”
If the technologies required to decommission the Fukushima reactors don't even exist yet, it means that they can de facto not be decommissioned at this point in time. It seems that the risk of something going seriously wrong (this is to say, even more wrong) remains extremely high.
The explosion at Fukushima in March 2011 after the tsunami
(Photo via bbc.co.uk)
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