On August 10, 2012, we reported to NISA on the details of the partial peel-off on the upper part of the fuel assembly channel box^*1 found in the past at Kashiwazaki-Kariwa Nuclear Power Station (overview of the matter, investigation conducted and measures implemented) in response to the verbal instructions received.

In accordance with the directive document^*2 regarding this matter received from NISA on the same day, we have been inspecting the fuel assemblies in the reactor and the spent fuel pool for the similar damage. (Previously announced on August 10, 2012)

As a result of inspecting the upper part of all the fuel assembly channel boxes in the spent fuel pool of Unit 1, 4 and 7 at Kashiwazaki-Kariwa Nuclear Power Station (which can be inspected at this point in time) by utilizing an underwater camera, the upper part of some of the channel boxes seemed to be whitened or damaged. The inspection results were put together as an interim report and submitted to NISA today.

The following is the outline of the inspection results.

[Kashiwazaki-Kariwa Nuclear Power Station]

As a result of inspection, possible whitening (maximum of approx. 19mm large) or damage was found on some of the channel boxes. However, such issue was found in our past inspections as well and there is no problem with the clip strength. Considering that the part which seems to be whitened or damaged is a fragile oxide, there should be no impact on the fuel assembly. Thus, this issue is not considered to be of risk to safety.

The channel box inspection at Fukushima Daiichi and Daini Nuclear Power Stations is to be considered as the top priority is the restoration from the Tohoku-Chihou-Taiheiyou-Oki Earthquake.

We plan to continue the investigation on this matter in accordance with the direction given. The channel boxes which seem to be whitened or damaged will be lifted up by the fuel handling machine for a detailed inspection utilizing an underwater camera. The cause of this matter will be investigated in consideration of the investigations conducted by other operators of electric utilities that received the same directive document, and the results will be reported to NISA.

End

Attachment
Outline of the "Partial Damage on the Upper Part of the Fuel Assembly Channel Box (Clip) Found at TEPCO's Nuclear Power Station (Interim Report)"(PDF 44.0KB)

*1 Channel box
Square metal tube cover installed on the fuel assembly. By installing the channel box, the coolant flow path through the fuel assembly can be fixed. It also functions as a guide when the control rods operate and protects the fuel assembly.

*2 Directive document
"Partial damage on the upper part (clip) of the fuel assembly channel box (Direction)" (August 10, 2012 NISA No.2)

The aforementioned documents are available only in Japanese. We apologize for the inconvenience this may cause.