Corporate Information

Press Release (Feb 12,2012)
Temperature increase of the lower part of the Reactor Pressure Vessel of Unit 2 at Fukushima Daiichi Nuclear Power Station
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. 
As the temperature of the lower part of the Reactor Pressure Vessel was not 
below 80°C, at 2:20 pm today, we judged that it does not clear one of the
"Conditions for operation"*2, which are provided in the Reactor 
Facility Safety Regulation*1.

When conditions for operation are not satisfied, as "Required countermeasures" *3,
it is required to take countermeasures against the temperature promptly, in 
order to clear the conditions. We therefore injected water with boric acid as
countermeasure to prevent from reaching re-criticality from 11:38 am to 1:50 pm
today, and from 2:10 pm to 3:30 pm today 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.

Although the temperature indicator for the lower part of the Reactor Pressure 
Vessel of Unit 2 is increasing at the point, as there is only one point where the
temperature is rising and with respect to other areas the temperatures tend to
decrease due to the increase of water injection amount, temperature indicators 
around the Reactor Pressure Vessel and in the Primary Containment Vessel show
decreasing and therefore the whole facility itself is presumed to be cooled, and 
we could assume that there is some water around the point at stake and that it 
cools down the point, judging from the relation between the entry pressure in the 
Primary Loop Recirculation System and the amount of water injection in the 
reactor feed water system, overall, we judge that cooling reactors works properly

Considering this event, at 3:22 am today, we conducted a sampling of gas in the
Primary Containment Vessel of Unit 2 and have found that each of short half-life 
nuclide Xe was below detection limit (9.5 x 10-2Bq/cm3) and the criterion
to judge re-criticality (1 Bq/cm3) and that there is no reaching criticality, 
and we have confirmed that there is no increase of radiation (Cs-134 and 137).

There is no significant variation of the values of monitoring posts around the 
site boundary of Fukushima Daiichi NPS and the consecutive dust monitors.

We will continue to the tendency of the temperatures, carefully.

*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. 
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