With regard to the temperature of the lower part of the Reactor Pressure
Vessel of Unit 2 at Fukushima Daiichi Nuclear Power Station, since
February 2, 2012, it has shown a gradual increase at one point in the part
and therefore we have kept changing the water injection amount and
monitoring the temperature. At 2:15 pm today, we confirmed that the
temperature indicator has reached 82°C.
At 2:20 pm on the same day, we judged that it does not clear one of the
"Conditions for operation"*2, which are provided in the Reactor Facility
Safety Regulation*1, and as "Required countermeasures" *3, we injected
water with boric acid as countermeasure to prevent from reaching
re-criticality, and we increased the water injection amount through the
core spray system from approx. 6.9m3/h to approx. 9.9m3/h. We also
adjusted the water injection amount through the reactor feed water system
from approx. 7.2m3/h to approx. 7.5m3/h. as it showed some fluctuation.
(Previously announced on February 12, 2012)
On February 13, we received an instruction document*4 titled "Submission
request for report on the correspondence for temperature increase in the
lower part of the Reactor Pressure Vessel of Unit 2 at TEPCO Fukushima
Daiichi Nuclear Power Station" from Nuclear and Industrial Safety Agency
(NISA) of Ministry of Economy, Trade and Industry, we have organized a
report including the assumed causes of the fluctuating temperature
readings of the thermometers, etc., regarding the temperature increase at
the lower part of the Reactor Pressure Vessel of Unit 2, and submitted the
report to NISA yesterday.
As result of conducting the temperature increase in the lower part of the
Reactor Pressure Vessel of Unit 2 at TEPCO Fukushima Daiichi Nuclear Power
Station, we judged that the thermometers had trouble.
(Previously announced on February 14 and February 16, 2012)
At 2:00 pm today, as result of conducting the thermometers concerned, we
judged that it does not deviate with the "Conditions for operation"
which are provided in the Reactor Facility Safety Regulation for the
temperature of the lower part of the Reactor Pressure Vessel of Unit 2, we
corrected an original judgment retroactively to on February 12.
And we decided to exclude the thermometers from the monitoring items for
the temperature of the lower part of the Reactor Pressure Vessel in Safety
Regulation Article 138 and we checked the temperature of the lower part of
the Reactor Pressure Vessel than other thermometers and we continuously
confirm that there is not critical state inside the Reactor.
We decrease the water injection amount into Unit 2 as soon as we are ready.
We try the maintenance of the cold shutdown state and the ensuring safety
of the plant continuously
End
*1 Reactor Facility Safety Regulation
Based on Clause 1, Article 37 of Act of the Regulation of Nuclear Source
Material, Nuclear Fuel Material and Reactors, it provides basic
conditions to be satisfied for operating nuclear power stations safely
and keeping it stable (operation management, fuel management, radiation
management, emergency treatment, and facility management based on
"Mid-term safety securing" etc.). It is approved by the national
government.
*2 Conditions for operation
Reactor Facility Safety Regulation provides necessary conditions such as
the numbers of the permitted machines etc. or criteria of temperatures
and pressures for securing multiple safety function for operating
reactors and for keeping nuclear power stations stable and these are
treated as conditions for operation. When there happen some malfunctions
of equipment provided in the regulation and a nuclear power station can
not clear the conditions temporarily, operators have to take required
countermeasures.
*3 Required countermeasures
Article 138 of Reactor Facility Safety Regulation provides that the
temperature of the reactor pressure vessels shall be below 80°C and that
if it rises over 80°C, operators shall take countermeasures against the
rising and clear the temperature condition for operation.
*4 Instruction document
Submission request for report on the correspondence for temperature
increase in the lower part of the Reactor Pressure Vessel of Unit 2 at
TEPCO Fukushima Daiichi Nuclear Power Station
(February 13, 2012, NISA)
We have provided a Japanese press release version of the instruction
document received from NISA. However, at this time we have reserved the
right not 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.