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)
