Top > Releases ･ Announcements > Press Releases > 2013 > Report on the Progress of Investigation on the Bent Fuel Assembly Water Rods Found at Kashiwazaki-Kariwa Nuclear Power Station (Follow-up Report)
Regarding the bent found on part of the spent fuel assembly water rods*1 at Unit 5 of Kashiwazaki-Kariwa Nuclear Power Station under regular inspection, we have received a directive document*2 "Bent fuel assembly water rods found at Unit 5 of TEPCO Kashiwazaki-Kariwa Nuclear Power Station (Direction)" from the Nuclear Regulation Authority on November 28, 2012.
(Previously announced on November 28, 2012)
In accordance with the directive document, appearance inspection of fuel assemblies is being performed at Units 1-7 of Kashiwazaki-Kariwa Nuclear Power Station and Unit 4 at Fukushima Daini Nuclear Power Station.
Today, the inspection of 68 fuel assemblies stored in Unit 1 at Kashiwazaki-Kariwa Nuclear Power Station has been completed. As a result, bent was found on part of 6 fuel assemblies and one of them was found to be causing the adjacent fuel rods to touch one another.
Similarly to the case found at Unit 5, the incident found at Unit 1 this time has been judged to apply to Article 19-17, Item 3*3 of the Rule for the Installation, Operation, etc. of Commercial Nuclear Power Reactors (Rule for Commercial Nuclear Power Reactors) considering that the fuel assembly shape is no longer being maintained.
As a channel box was installed on these fuel assemblies in concern (at Units 5 and 1) under water before being loaded in the reactor as fresh fuels, the cause of the water rod bending is considered to be the excessive force applied when installing the channel box, which was previously assumed.
Based on the inspection results obtained, we will continue investigating the cause of the water rod bending. The investigation results will be reported to the Nuclear Regulation Authority.
*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 Directive document
"Bent fuel assembly water rods found at Unit 5 of TEPCO Kashiwazaki-Kariwa Nuclear Power Station (Direction)"
*3 Article 19-17, Item 3 of the Rule for the Installation, Operation, etc. of Commercial Nuclear Power Reactors (Rule for Commercial Nuclear Power Reactors)
As stipulated by Article 62-3 of the Act on the Regulation of Nuclear Source Material, Nuclear Fuel Material and Reactors, in the case of an incident which applies to the following, licensees of reactor operation (including former licensees of reactor operation, same as in the following Article and Article 24) must report the incident and countermeasures to the Nuclear Regulation Authority within 10 days from the incident occurrence.
When licensees inspect equipments critical for ensuring safety and the results do not comply with the standards stipulated in Article 9 or Article 9-2 of the Ordinance which specifies the technical standards of commercial nuclear power facilities or when the functions necessary to maintain safety of nuclear facilities are deemed inadequate.
The aforementioned documents are available only in Japanese. We apologize for the inconvenience this may cause.
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