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
Rules on the Installation, Operation and Others of Commercial Nuclear Rectors for
Appendix: Structure and Position of the Control Rod Drive's Coupling in Unit No.6(PDF 74.5KB)