Press Releases 2013

On October 16, 2012, 2 spent fuel assembly water rods^*1 were found to be partially bent^*2 at Unit 5 of Kashiwazaki-Kariwa Nuclear Power Station under regular inspection. In response to this, we have received a directive document^*3 from the Nuclear Regulation Authority on November 28, 2012. Based on the directive document received, we are currently performing appearance inspection of fuel assemblies at Kashiwazaki-Kariwa Nuclear Power Station. The similar inspection will be performed at Unit 4 of Fukushima Daini Nuclear Power Station starting from March 6, 2013. The inspection will be performed on spent fuel assemblies (35) on which a channel box^*4 was installed under water before the installation method was changed in 1998.

We will continue performing the inspection currently being done at Kashiwazaki-Kariwa Nuclear Power Station at other nuclear power stations to understand the water rod conditions and the cause of the water rods being bent while performing tests utilizing fuel assembly mockup and evaluating the impact of this incident on safety.

The inspection results will be reported to the Nuclear Regulation Authority once they are prepared.

*1 Water rod
Hollow tube installed in the center of the fuel assembly in parallel with fuel rods. By passing water through the tube, the output inside the fuel assembly is optimized.
*2 Partial bent on the water rod
The water rod is assumed to be bent as a result of applying excessive force when installing a channel box. Based on the investigation (mockup test) results so far obtained, it was confirmed that there is a possibility of water rod bending due to excessive force applied when installing a channel box. After the channel box installation method was changed, the force to be applied on the fuel assembly during installation has been controlled and thus no bending has been found.
*3 Directive document
Bent fuel assembly water rods found at Unit 5 of Kashiwazaki-Kariwa Nuclear Power Station (Direction)
*4 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 fuel assembly.

The aforementioned document is available only in Japanese. We apologize for the inconvenience this may cause.