Unit 2 Temperature rising

Fukushima Update #79, February 11, 2012

by Nelle Maxey

This is getting serious.

RPV Temperature at 74.9 degrees C (highest since this whole tragi/comedy began) and cooling water increased to 14.5 tons/hour.

Can TEPCO stop this run away train? Especially since they don't really know what is going on .

chart of water and temperature

Trend lines show that despite the large volumes of cooling water being injected into Unit 2, the temperature is RISING.

As you see from the story below, no one was aware of the actual trend in the temperature shown on my charts.
Temperature at Reactor 2's RPV Bottom Shoots Up to 75 Degrees Celsius

Saturday, February 11, 2012
"TEPCO's plant parameters on temperatures haven't been updated yet to reflect the number, but Jiji Tsushin reports that the temperature at the bottom of the Reactor Pressure Vessel of Reactor 2 at Fukushima I Nuclear Power Plant shot up to 74.9 degrees Celsius as of 11PM on February 11, Japan Time.

"The temperature at this location has been trending in the upper 60s, but TEPCO's Matsumoto and his junior PR manager (who can only read what's given to him) have been saying the temperature "is trending down". In TEPCO-speak, remaining at a high temperature is clearly "trending down", because it is not going up.
From Jiji Tsushin (2/11/2012):
"One of the three thermometers at the bottom of the Reactor 2 Pressure Vessel that had been trending in the upper 60s started to rise again in the evening of February 11. In response, TEPCO has increased the amount of water being injected into the RPV by 1 tonne per hour to 14.6 tonnes per hour. As of 11PM on February 11, the thermometer showed 74.9 degrees Celsius, while the other two thermometers placed at the same height were trending around 35 degrees Celsius.
The temperature is the highest since the rising trend started on February 1, and the amount of water being injected into the Reactor 2 RPV now is the highest ever since March 11, 2011.
"Since the margin of error may be as much as 20 degrees either way, 5 more degrees to go until the temperature at that location may be reaching 100 degrees Celsius."

The recent temperature rise at Unit 2 received a flurry of attention in the international press and on blog sites a few days ago, but has pretty much died down. However all is not well yet.

The Operational Limits requirements for any of the Fukushima reactors to be classified in (TEPCO-defined) "cold shutdown" have two conditions.

The first condition is that the temperature remain below 100 degrees centigrade.
To meet this requirement, TEPCO has been publishing the temperature measured at the bottom of the RPV (reactor pressure vessel) which contains the melted nuclear fuel rods on a twice daily basis since the accident. When Unit 2 began to heat up at the beginning of February, TEPCO announced this problem in their daily press releases and began altering the flow of cooling water into and around the RPV to lower the temperature. The problem arose when TEPCO changed the flex pipe carrying cooling water to the reactors to solid plastic pipe in mid-January. (Probably to avoid freezing and leakage problems, though this is nowhere specified by TEPCO). During this change-out process, the levels of cooling water were altered significantly and the RPV at Unit 2 began to heat up. TEPCO has published more detailed temperature charts during this heat-up, culminating in the publishing of near hourly temperature readings on their website yesterday. Since the temperature has somewhat stabilized, the press has lost interest in this issue however.

Which takes us to the second condition in the operation limits. In order to retain "cold shutdown" status, the total volume of cooling water can not be adjusted by more than 1 metric ton (cubic meter) per day. Prior to changing the piping the total volume of cooling water injected into Unit 2 were averaging 10 tons per hour. As you see in the chart, volumes of cooling water have been increased by more than 3.5 tons per hour in order to stabilize the temperature. TEPCO alludes to this in their morning press release on Feb 7, but the English translation is so garbled, it is not surprising the point is not well understood:

"In the Chapter 12 of Nuclear Reactor Facilities Security Regulation "The Way of Ensuring Mid-term Security", as the treatments like "Operational limitation" or "Measures required in case of not satisfying the operational limitation" are determined, it is supposed the operator act per the required measures if it fails to satisfy the operational limitation. This time, to implement maintenance works, we changed the amount of water injection into Unit 2 (from 3:48 am on February 7) by conducting a planned shift beyond the range of operational limitation."

All the press stories and blogs I have read discuss only the temperature requirement. No one is discussing the increased water volume requirement.

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