In response to the bent found on part of the water rods of 2 spent fuel assemblies while inspecting the upper part (clip) of fuel assembly channel box at Unit 5 of Kashiwazaki-Kariwa Nuclear Power Station (under regular inspection), we have inspected the appearance of 65 fuel assemblies to check for similar conditions. As a result, 18 out of the 65 fuel assembly water rods were found to be bent.
2 out of these 18 spent fuel assemblies on which major bent was found were inspected further utilizing a fiberscope. As a result, the following conditions have been found.
- Deformation was found near the hole on the thin area in the lower part of water rod where strength is relatively low.
- Though some holes have become smaller due to deformation, no hole was completely closed.
- The fuel rods adjacent to the bent water rods were touching or close to one another.
As fuel rods were found to be touching one another due to the bent water rods, it has been judged by the Nuclear Regulatory Agency that the incident applies to Article 19-17, Item 3 of the Rule for the Installation, Operation, etc. of Commercial Nuclear Power Reactors (Rule for Commercial Nuclear Power Reactors). (Previously announced on December 12, 2012)
We have submitted a report regarding the bent fuel assembly water rod found at Unit 5 of Kashiwazaki-Kariwa Nuclear Power Station to the Nuclear Regulation Authority today in accordance with "Article 19-17, Item 3 of the Rule for the Installation, Operation, etc. of Commercial Nuclear Power Reactors (Rule for Commercial Nuclear Power Reactors)".
In response to the directive document* received from the Nuclear Regulation Authority on November 28, 2012, we are currently carrying out inspection in other units. As a result of inspecting 31 fuel assemblies in Unit 2, part of the 2 spent fuel assembly water rods were found to be bent (approx. 1.5cm).
As for these 2 fuel assemblies, the water box was installed under water before loading in the reactor as unused fuels (similarly to Unit 5). The cause of the bent water rods is considered to be the same as previously estimated (water rods were bent because of the excessive force applied while installing the channel box).
In accordance with the directive document received from the Nuclear Regulation Authority, we will continue inspection and further investigate the cause of the incident. The results will be summarized and submitted to the Nuclear Regulation Authority.
Reactor Facility Failure Report (Title: Fuel rods touching one another at Unit 5 of Kashiwazaki-Kariwa Nuclear Power Station) (PDF 13.8KB)
Overview of the bent fuel assembly water rods found at Unit 2 of Kashiwazaki-Kariwa Nuclear Power Station (PDF 44.3KB)
* Directive document
Bent fuel assembly water rods found at Unit 5 of Kashiwazaki-Kariwa Nuclear Power Station (Direction)
The aforementioned documents are available only in Japanese. We apologize for the inconvenience this may cause.