via EX-SKF / May 7, 2014 / As of May 7, 2014, 814 fuel assemblies (22 new (unused) assemblies, 792 used fuel assemblies) out of the total 1533 in the Reactor 4 Spent Fuel Pool have been successfully removed.

Removal of the fuel assemblies in Reactor 4’s SFP started on November 18, 2013. At this pace, it will be completed sometime in November this year, as scheduled.

From TEPCO’s English page on Reactor 4’s SFP fuel assembly removal (which has been updated finally, to my surprise):

 

This job seems to be about the only one job at Fukushima I Nuclear Power Plant these days that is carried out without a major glitch or accident, though with a significant radiation exposure to the workers who manipulate the Fuel Handling Machine on the platform above the pool to remove the fuel assemblies. The bulk of radiation comes not from radioactive cesium but cobalt-60 in the water, according to Nuclear Regulation Authority.

SOURCE: EX-SKF.blogspot.com

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By Broc West| 4 Comments | Featured, News

4 comments

  1. 792/1331 = 60% of the spent fuel is removed. The worst possible decay heating is down to 18% of the level when the tsunami struck. This is based on the decay heat from the remaining 539 most hot fuel rods.

    The Co-60 comes from reactor “shavings”, Im not sure why Tepco needed to cut into the reactor. Co-60 becoming the primary source source of radiation for SFP4 is good news. This means the workers are exposed less to the sent fuel fission products.

  2. The delay in updating is probably due to Golden Week, a series of holidays that occur around the beginning of May each year in Japan. The English-language pages weren’t translated and published during this time, same with the NRA sea and land radioactive measurement reports.

  3. I finally dug deep enough through the blog-chain to discover the Co-60 report mentioned in the top article. A high level of activity attributed to Co-60 was discovered in particles removed from Spent Fuel Pool 4 but only from that source, it seems. The radiation exposure to workers on the fuel handling floor is going to be almost entirely from fallout from the explosions that was deposited on the building structure rather than sand/concrete particles several metres under water from where they are working. Remember too that the fuel rods remain underwater at all times as they are transferred to the transport casks so there is no airpath for direct radiation exposure to the workforce from the rods themselves.

    The fact there is any Co-60 in the pool is interesting in itself — activation of Co-59 by neutrons been a well-known phenomenon since the 50s and low-cobalt and no-cobalt steel alloys are specified in reactor designs where high neutron fluxes are expected, the reactor pressure vessel for example. There is some Co-60 produced from fission but usually very little compared to the mid-range isotopes like I-131 or Cs-134/137 (each about half the mass of a U-235 atom).

  4. Interesting headline 60% of one reactor is only ~15% of all four reactors fuel.. So the headline should say 15% right?
    Of course the remaining reactors being melted down creates some serious difficulty and exposure removing the rest… I pray for the workers health..

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