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Press Release (Jun 01,2011)
Receipt of written direction regarding the implementation of necessary measures for fire prevention in relation to overhang-type high-voltage breakers at nuclear power stations
We received the written direction "regarding the implementation of 
necessary measures for fire prevention in relation to overhang-type 
high-voltage breakers at nuclear power stations" (*) from Nuclear and 
Industrial Safety Agency (NISA), Ministry of Economy, Trade and Industry. 
Following this instruction, we will promptly take response and summarize 
this matter, and report them to NISA.

*Written direction 
Regarding the implementation of necessary measures for fire prevention in 
relation to overhang-type high-voltage circuit breakers at nuclear power 
stations (direction)
                                                      (05.30.2011 NA No.2)

On May 30, 2011, Nuclear and Industrial Safety Agency (hereinafter 
referred to as "NISA") received a report from Tohoku Electric Power Co., 
Inc. on the status of Onagawa NPS following the 2011 off the Pacific Coast 
of Tohoku Earthquake and the ensuing tsunami. 
According to this report, a fire broke out on the high voltage normal 
distribution panel at Unit 1 of the aforementioned NPS on March 11. The 
fire is understood to have been triggered when seismic motion caused an 
overhang-type high-voltage breaker of the distribution panel to swing, 
bringing the bonding conductor into contact with the surrounding structure 
and creating a short or a ground, which in turn caused an arc discharge 
with heat sufficient to touch off a fire. Based on this report and in 
order to prevent similar fire incidents, NISA issued a written direction 
(see appendix) today, May 31, to commercial power reactor licensees to 
verify the presence if any of overhang-type high-voltage breakers at NPSs 
owned by these licensees, and should such a breaker be present, draft an 
implementation plan for necessary measures for fire prevention such as 
upgrading to a high-voltage breaker with highly seismically-resistant 
design or installing a seismic trestle on the lower part of the 
overhang-type breaker, and report this to NISA by June 15 of this year.
(Translation by NISA; http://www.nisa.meti.go.jp/english/press/2011/06
                      /en20110610-3.pdf)

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