Corporate Information

Press Release (Jun 27,2008)
RE: Defective Coupling between a Control Rod Drive and the Corresponding Control Rod in Unit No.6 of Kashiwazaki-Kariwa Nuclear Power Station
TEPCO has been conducting the 8th regular inspection for Unit No.6 (Advanced Boiled 
Water Reactor with a rated output of 1,356 MW) of its Kashiwazaki-Kariwa Nuclear Power 
Station since May 24, 2007. Functional tests for the control rod drives (205 in total) 
have been conducted since June 2, 2008 to validate their soundness following the 
Chuetsu-Oki Earthquake*1. Today, we found out that one control rod drive was not coupled 
with the corresponding control rod*2, and hereby announce this fact since we judged 
that this was an event to be reported under the Decree*3.

All fuels had been taken out of the reactor of Unit No.6 and thus there is no safety 
issue. As for the remaining 204 control rod drives, we have confirmed that all were 
properly coupled with their respective control rods.

The coupling in question had been visually inspected by an underwater camera and no 
damage was found. Therefore, we suppose that the defective coupling is not related 
with the Chuetsu-Oki Earthquake. We will carry out detailed investigation for the cause.

*1 Functional tests made on control rod drives (205 in total) to check their soundness 
   following the Chuetsu-Oki Earthquake
   Functional test to validate the soundness of control rod drives as part of post-quake 

*2 Control rod
   The control rod in question had been replaced during this regular inspection. All 
   control rods had been fully inserted for regular inspection when the earthquake 

*3 Decree
   Rules on the Installation, Operation and Others of Commercial Nuclear Rectors for 
   Power Generation.  

Appendix: Structure and Position of the Control Rod Drive's Coupling in Unit No.6(PDF 74.5KB)
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