On March 2, 2012, we confirmed that in the Unit 5 of Kashiwazaki Kariwa
nuclear power station (boiling-water reactor, rated output is 1,100MW),
which was under a regular inspection, an air isolation dumper (valve) of
the emergency air ventilation systems in the main control room*1 was
unable to close due to regular inspections, during some radiated fuel work
(moving control rods and external inspection of spent fuel) on February 25
and 27, 2012, and did not satisfy a restriction for operation*2 for a
while, although a safety regulation for reactor facilities of Kashiwazaki
Kariwa nuclear power station provides that work related to the radiated
fuel in reactor buildings is only allowed when the both of the 2 emergency
air ventilation systems in the main control room are workable. 
                                    (previously announce on March 2, 2012)

Today we have received an instruction document*3 from Nuclear and
Industrial Safety Agency (NISA) of Ministry of Economy, Trade and Industry
concerning this event.

With this event, as a result of researches so far, we have found:
- that an operation worker of Unit 5 mistakenly thought that as long as
  the other dumper which is installed in the upstream of the dumper at
  stake (valve) works, no violation of the rule is caused and therefore
  allowed workers to work on radiated fuel under the situation stated in
  the above.
- that the worker did not recognize that an internal rule of the power
  station provides that inspections for emergency air ventilation in the
  main control room and radiated fuel work are not allowed to be conducted
  at the same period but that among regular inspections for emergency air
  ventilation, only the inspection for the dumper at stake was planned to
  be conducted at the same period of the radiated fuel work.

We assume, from this research result, the cause of this event is the
correct interpretation for the restriction of operation provided in the
safety regulations was not shared enough with the workers 

Based on the instruction document, we will further investigate the causes,
establish countermeasures to prevent the same kind of errors and report to
NISA.

                                                                       END

*1 Emergency air ventilation systems in the main control room
Air conditioning equipment installed separately in order to operate and
take measures in the main control room without the workers exposed to
excessive radiation at accidents. There are 2 systems of these and only
one system can provide 100% capacity.

*2 Restriction for operation
Safety regulations provide a "restriction for operation" with regard to
reactor operation and in this case it provides that when workers work on
radiated fuel, both of the 2 systems of emergency air ventilation systems
in the main control room (2 fans, 1 filter unit and necessary dumpers
(valves) and duct) shall be workable.

*3 Instruction document
"Violation of safety regulations for the operation of emergency air
ventilation syststems in the main control room of Unit 5 of Kashiwazaki
Kariwa nuclear power station (instruction)"
                                              (March 15, 2012, NISA, No.3)

*We have provided a Japanese press release version of the instruction
document received from NISA. However, at this time we have reserved the
right to provide an English version due to potential misunderstandings
that may arise from an inaccurate rendering of the original Japanese text.
We may provide the English translation that NISA releases in our press
releases. However, in principle we would advise you to visit the NISA
website for timely and accurate information.