NRA announced the dry cask for spent fuel of Fukushima plant might be overly vulnerable

On 12/4/2015, NRA (Nuclear Regulation Authority) announced that the dry cask to store the spent fuel assemblies can be excessively vulnerable.

In order to stock the fuel assemblies of SFP 4 (Spent Fuel Pool of Reactor 4) in the common pool, Tepco transferred the fuel assemblies from the common pool to the dry cask.

By the end of October 2014, Tepco had stocked 28 dry casks to contain 1,412 fuel assemblies. They were planning to transfer additional 1,600 fuel assemblies to more 23 dry casks. NRA reports that only 11 casks of this issued type are in actual use in Fukushima plant.

According to NRA, there is a possibility that an internal part of dry cask doesn’t have enough strength. It was designed based on the standard of the Japan Society of Mechanical Engineers, however the standard was abolished this October, just before this scandal became public, because it did not have enough basis and overrated the strength.

https://www.nsr.go.jp/data/000131890.pdf

https://www.nsr.go.jp/disclosure/committee/roanshin_kakunen/00000003.html

http://www.nsr.go.jp/data/000051156.pdf

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