Secret Cask Structure

As you may have heard, TEPCO started removing fuel elements from the spent fuel pool of reactor 4 at Fukushima Daiichi NPP. Looking through some images of the operation TEPCO released this Friday, I noticed a peculiar note:

“These photos include information concerning physical protection, etc. and therefore include altered parts.”

Obviously, I immediately became curious as to what the secrecy was about. Looking through the images as well as some older ones, I quickly discovered that the pixelated parts covered the transport cask’s internal structure as well as the attachment points for the crane, as you can see in the images below (if they’re too small, click the images for larger versions, or visit TEPCO’s media library).

Fuel transport cask in a water filled pit, with one fuel element lifted
Photo: TEPCO, released on 2013-11-22

I understand that TEPCO “cannot make public the detailed date of fuel transfer, etc. for security reasons” as stated in the press release, but why keep the structure of the NFT-22B fuel transport cask secret? If it is designed properly, it should be able to hold up to outside scrutiny, if not, it shouldn’t be used. However, I do not know if the decision to hide it was made by TEPCO, or if it was required by Japan’s nuclear safety regulations. That they’re openly mentioning the alterations is certainly a good thing. Interestingly, a presentation (in Japanese) also released by TEPCO describing the fuel removal operation does contain a schematic diagram of the NFT-22B in section 8.

Fuel transport cask hanging on a crane inside the cover around Fukushima Daiichi reactor building 4
Photo: TEPCO, released on 2013-11-18

Maybe it is interesting to you that the first two words in red on the banner in the background mean “Don’t fall!” and “Don’t drop!”, although the image is too blurry for me to read the rest. You can find more images in TEPCO’s media library.

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