Ooi Nuke Plant Reactor 4 Had 137 Alarms Set Off in 10 Days, But "Not A Problem", Says KEPCO

KEPCO seems to have much thicker skin than TEPCO, if that's even possible.

KEPCO says the alarm at one of the thermocouples inside the Reactor 4 Pressure Vessel has been triggered 137 times since the reactor started the full operation on July 25, but it's not a problem, things will sort themselves out soon.

From Mainichi Shinbun Fukui local version (8/3/2012):

関西電力は２日、大飯原発４号機（１１８万キロワット）の原子炉内の１次冷却水の温度が部分的に上昇したことを示す警報が同日午後３時現在で計１３７回作動したと発表した。警報は４号機がフル稼働に入った７月２５日早朝に初めて作動。燃料集合体（１９３体）のうち１体について、周辺の冷却水の温度が警報基準に達した。

KEPCO announced on August 2 that an alarm was sounded 137 times as of 3PM that day which indicated the rise in local temperature of the primary coolant [water] inside the Reactor Pressure Vessel in Reactor 4 (1.18 million kilowatts) at Ooi Nuclear Power Plant. The alarm was first sounded in the early morning on July 25, when the reactor started the full operation. The temperature of the coolant around one of the nuclear fuel assemblies (193 assemblies total) rose to the level that would trigger an alarm.

　関電によると、過去に１回使用した比較的燃焼度の高い燃料だったため、流量の変化で一時的に冷却水の温度が上がった。燃焼度に応じた燃料全体の配置に問題はなく、今月中旬ごろには安定した状態になるとみている。

According to KEPCO, the particular fuel assembly had been used once before and had relatively high fuel burnup. The company says that a change in the amount of flowing water temporarily raised the temperature of the coolant. KEPCO doesn't think there is any problem with the fuel assembly arrangement based on the fuel burnup, and says the temperature will stabilize by the middle of this month.

　また、７月３０日には取水口付近に漂着したクラゲの影響で３、４号機が共に取水量を抑えたため発電出力が最大約１・８％落ちた。

On July 30, the power output was decreased by 1.8% as both Reactors 3 and 4 reduced the amount of seawater intake because of jellyfish.

(So jellyfish are still protesting...)

KEPCO's press release on 8/2/2012 includes their explanation (in the attachment No.3) of why the alarm is being triggered and why it is no problem, in a very technical term (again, they outdo TEPCO).

From what I could figure, the thermocouple at this particular fuel assembly has been registering temperature higher than the standard (between 305 and 336 degrees Celsius), but it is because this assembly has high fuel burnup having been used once already, and as the time goes the relative output of the fuel assembly will drop, and the temperature will drop. The current cycle is the cycle No.15, and KEPCO uses more fuel assemblies that have been used once than in the previous two cycles, so the higher temperature is to be expected. As long as the temperature is below the saturation temperature (345.3 degrees Celsius), there is no problem with cooling.

(I put the English labels. KEPCO's press releases in English are almost all about financial results for the investors. They do have an English press release on the restart of Ooi Nuke Plant, dated June 16, 2012, if you're interested, here.)

Ooi Nuclear Power Plant's two reactors are both pressurized-water reactors from Mitsubishi Heavy Industries.

The temperatures of the coolant inside the PWR, according to wiki, is 275 degrees Celsius as the water enters the RPV at the bottom, and 315 degrees Celsius as it flows upward to the reactor core.

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Only Two Thermocouples Remaining to Measure Reactor 2 Pressure Vessel Temperature?

TEPCO's "Status of TEPCO's Nuclear Power Stations after the Tohoku-Chihou-Taiheiyou-Oki Earthquake (Daily Report as of 3:00 pm, April 19)" states:

On April 18, we evaluated the reliability of the thermometer (RPV bottom head 135°) which was monitored for reference based on safety regulations 138 through direct current resistive measurement. We evaluated the thermometer broken down based on the increase in direct current resistance. No large swings confirmed at other thermometers, monitoring posts, and PCV gas management system indicators. We will continue monitoring PCV temperature by thermometers (RPV bottom upper head 270° and RPV upper skirt junction 135°)

The failure of the thermocouple "69H2" (at RPV bottom head at 135 degrees) was noted in the blog post on April 15. So now there are two thermocouples left on the RPV of Reactor 2 - 69H3 and 69F2 - to measure temperatures to make sure the reactor is in the "cold shutdown state".

(Pay attention to the word "state", which makes this "cold shutdown" uniquely Japanese.)

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#Fukushima I Nuke Plant Reactor 2 RPV: 2 More Thermocouples Gone Bad

Now, there are only 15 thermocouples left on the Reactor Pressure Vessel of Reactor 2 that are more or less working. Before the accident, there were 31 thermocouples on the RPV monitoring the temperatures, according to Yomiuri Shinbun (3/3/2012).

The thermocouple at the RPV bottom at 0 degree, 69H1, has already been declared failed (after TEPCO tested it...), and now 69H2 at 135 degrees is considered failed, as DC resistance is too low for a properly functioning thermocouple. Now, the thermocouple at 270 degrees, 69H3 is the only one measuring the temperature at the RPV bottom.

The other thermocouple gone bad is 69F3 at the junction of skirt supporting the RPV at 270 degrees.

According to Yomiuri, TEPCO plans to install new thermocouples by the end of July. No information about how.

From TEPCO's handout for the press, 3/3/2012 (reference, in English):

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#Fukushima I Nuke Plant Reactor 2 RPV: Temperatures at Bottom Seen Rising, Diverging

Something is going on inside or outside Reactor 2 Pressure Vessel. Either more thermocouples could be failing, or those that were deemed failed weren't failing.

Here's the latest temperature reading of the Reactor 2 RPV bottom from TEPCO (2/24/2012):

Notice:

1. Gradual temperature divergence between 69H2 (now the "official" temperature gauge of the RPV bottom after 69H1 at 0-degree supposedly "failed") and 69H3 (first 2 columns after the date and time column). Up till February 22, the temperature difference between these two thermocouples was 1 degrees Celsius. The difference started to widen on February 22, widened further on February 23, shrinking a little on February 24.

2. Overall rising trend of temperatures at all thermocouples at "the bottom head" and "support skirt junction". At 6PM on February 18, all temperatures measured at this location was below 30 degrees Celsius; at 5PM on February 24, temperatures are in the upper 30s to mid 40s.
   

No insight from the media there as to why this may be happening. I'll watch TEPCO's press conference archive later to see what TEPCO had said while I wasn't blogging.

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Temperature at Reactor 2 RPV Thermocouple (69H1) Slowly Coming Down

It doesn't look like the behavior of a thermocouple that has been broken, but what would I know?

From TEPCO's plant parameter, Reactor 2 RPV temperatures, hourly (latest: 2/15/2012 10AM):



In the meantime, the temperature at the CRD (control rod) Housing has been rising again. Again, instrument failure. (Brown line in the graph. 69H1 is light green.)

From TEPCO's plant parameters, Reactor 2 RPV temperature (2/15/2012):

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#Fukushima I Nuke Plant Reactor 2 RPV: 8 Thermocouples out of 41 Show Abnormality, TEPCO Says

From Kyodo News (2/14/2012):

福島第１原発２号機で原子炉圧力容器底部の温度計の数値が異常に上昇した問題で、東電は１４日、他の温度計の点検を進め、圧力容器に４１個ある温度計のうち計８個に異常がみられると発表した。

As the temperature at the bottom of the Reactor 2 Pressure Vessel shot up extremely high, TEPCO announced on February 14 that the company had conducted the test of 41 thermocouples on the RPV, and found 8 of them showing abnormality.

　一時、４００度を超えた温度計１個のほか、２個に温度を測るもととなる電気抵抗値に異常が見つかった。残りの５個は故障と判断していた。東電は残る３３個の温度計で圧力容器全体の温度傾向を監視する。

In addition to the thermocouple that exhibited the temperature above 400 degrees Celsius, 2 other thermocouples had abnormal electrical resistance. 5 had been deemed broken. TEPCO will continue to monitor the temperature trend of the RPV with the remaining 33 thermocouples.

　経産省原子力安全・保安院から、故障とみられる温度計に代わる温度監視の策を求められたことについて、東電は「新たに温度計を設置するのは難しい。実現可能性含め対応したい」としている。

As for the request from the Nuclear and Industrial Safety Agency to submit a plan to monitor the temperatures at the locations where the thermocouples failed, TEPCO says, "It is difficult to replace the thermocouple, but we would like to consider further whether it is possible at all."

8 out of 41 showing abnormality? That's not quite what I read in the TEPCO's report in December 2011. Page 1-64 of the report has a table that shows the numbers of thermocouples in Reactors 1, 2, 3 that were evaluated with equivalent circuit. In the case of Reactor 1 RPV,

• No. of thermocouples that can be used with equivalent circuit: 32

• No. of thermocouples that cannot be used with equivalent circuit: 1

• No. of normal (functioning) thermocouples: 2

So, as far as I can understand (correct me if I'm wrong, as I could be very wrong) one of the 32 thermocouples on the Reactor 2 RPV shows a certain value, and TEPCO compares it with the value of the equivalent circuit, and figure out over time whether the value shown by the thermocouple can be used after equivalent circuit calibration.

TEPCO's report says the standard deviation for Reactor 1 RPV's thermocouples is about 15 degrees Celsius, and 8 degrees Celsius for Reactor 2 RPV's thermocouples. Thus the margin of 20 degrees Celsius mentioned by TEPCO for the maintenance of "cold shutdown state", I think, to be on the safe side of 15 degrees Celsius.

The report says 14 thermocouples on the Reactor 3 RPV can be used with equivalent circuit calibration, while 18 thermocouples cannot. There is no normal thermocouple on the Reactor 3 RPV.

Hmmm. Maybe it is Reactor 3 we should be worrying about.

FYI, the latest temperature information of Reactor 3's RPV is here.

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Reactor 2 RPV Bottom Temperature at Support Skirt Junction Also Fluctuating Widely

The location whose thermocouple (69H1, bottom head) apparently broke after the resistance test by TEPCO yesterday and the location at the support skirt junction are both located at 0 degree.

The thermocouple at the support skirt junction, 69F1, is not spiking up or continuously trending up like 69H1, but the range of fluctuation is rather wide, compared to the other two at the same height at different angles.

Hmmm. Next to go?

From the latest plant parameter on Reactor 2 RPV temperature, hourly, 69H1 (bottom head at 0 degree) and 69F1 (support skirt junction at 0 degree) highlighted:

Hourly temperature fluctuation at the thermocouples at the support skirt junction:

69F1 (at 0 degree): by 0.1 to 11.7
69F2 (at 135 degrees): by 0.1 to 0.3
69F3 (at 270 degrees): by 0.1 to 0.2

By the way, TEPCO released the graph of the thermocouple 69H1 (2/13/2012). It sure looks like TEPCO's resistance test did something:

People are chiming in on Japanese Twitter, saying "Yes I've done exactly that, pushing one test too far..."

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#Fukushima I Nuke Plant: Additional Info on That "Broken" Thermocouple on Reactor 2 RPV

From Yomiuri Shinbun (2/13/2012):

東京電力は１３日、温度上昇を示していた福島第一原子力発電所２号機の原子炉圧力容器底部の温度計が同日午後の点検後、記録上限の４００度を超えて振り切れるなど、異常な数値を示したと発表した。

TEPCO announced on February 13 that the thermocouple on the bottom of the Reactor 2 Pressure Vessel at Fukushima I Nuclear Power Plant, which had been showing the rising temperature, exhibited the abnormal temperatures after the inspection in the afternoon on February 13, at one time going overscale over 400 degrees Celsius which is the limit.

　東電は「ほぼ確実に故障している」とみている。温度計は炉心溶融で高温にさらされた後、湿度の高い環境に置かれていた。

TEPCO thinks it is "most certainly broken". The thermocouple had been exposed to high temperature from the core meltdown, and has been in the high humid condition [inside the Reactor 2 Containment Vessel].

　東電は同日午後２時頃から、中央制御室内で温度計の電気回路の点検を実施。回路の電気抵抗が通常より大きく、温度計の指示値が高く出やすいことが判明した。検査直後、回路を元に戻した際には３４２度を示し、一時振り切れるまで数値が上昇した。

TEPCO conducted the test of the electric circuit of the thermocouple from the central control room from 2PM. The electrical resistance was higher than normal, which would result in the temperature indicated by the thermocouple higher [than the actual temperature]. Right after the test, the temperature showed 342 degrees Celsius, and it rose sharply at one time and went overscale.

　温度計は、２種類の金属を接合したセンサー（熱電対(ねつでんつい)）で温度を検知する。センサーが熱を受けると電流が流れる仕組みで、回路に異常が生じたために電圧が変化し、極端な値が表示された可能性がある。

The thermocouple is a bi-metal sensor to detect temperature. It produces a voltage when it is heated. It is possible that an abnormality occurred in the circuit which caused the voltage to change, resulting in the extreme measurements displayed.

In the press conference yesterday, TEPCO's Matsumoto said it was a copper-constantan thermocouple. Constantan is a copper-nickel alloy.

I was watching the press conference live, and was quite amused that TEPCO's Matsumoto and the junior PR manager were rather put off and irritated at some of the senior journalists who kept asking tough questions. They are not the usual fixture these days at TEPCO's press conferences.

These journalists, unlike the regulars (dwindling number, these days) who are mostly young boys and girls in their 20s and early 30s at most who hunch over their laptops and ask questions from behind the laptop display screen while they type, looked straight into Matsumoto, and ask questions with a pen in hand and a notebook on the desk.

Old fashioned way of journalism, which I thought was refreshingly effective. You have to knock TEPCO's PR people out of their kilter to get an edge and draw answers which TEPCO didn't intend to give.

As I mentioned in my post reporting the press conference, Matsumoto was particularly announced by the 2 questions:

One was posed by a reporter from Yomiuri Shinbun (he's a regular). The reporter asked if the test itself broke the thermocouple. (Bingo...) Matsumoto denied the possibility, saying the test was conducted distantly from the central control room, not at the thermocouple (no way, as it is inside the CV).

The other was posed by an independent journalist who kept asking Matsumoto if TEPCO was consulting the manufacturer of the thermocouple for insight and technical assistance. That really set off Matsumoto, who immediately said TEPCO was fully capable of the maintenance of the thermocouples at the plant. Despite repeated questions, Matsumoto refused to give the name of the manufacturer or whether the representative of the manufacturer was on hand at Fukushima I Nuke Plant.

Never mind that this is not an ordinary maintenance of the thermocouples in a functioning reactor.

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TEPCO Evening Press Conference 2/13/2012: Reactor 2 RPV Thermocouple Is Broken, Matsumoto Says

Press conference live link is here.

Reactor 2 RPV's thermocouple that's been going up seems to have finally broken. (0r else...)

15:00 285.4 degrees Celsius
16:00 260.9
17:00 275.9

Screen capture from the press conference screen:

The last time this particular thermocouple went to that level, it was March 2011.

TEPCO was measuring the electrical resistance of the thermocouple before the temperature suddenly shot up to 285 degrees at 3PM.

Resistance 500 to 530 ohm.

The instrument has totally failed, says TEPCO's Matsumoto.

Interesting question from a reporter from Nico Nico: Are you going to test the other two thermocouples at the bottom of the RPV?
A: No.

Yomiuri: Did measuring the resistance break the thermocouple?
A: We don't know why the temperature shot up after we finished the measurement.

Yomiuri: Do you know when this thermocouple broke?
A: At least, until the end of January it was showing the same trend as the other two. We want to carefully compare with other thermocouples.

===========================
Jiji Tsushin says right before 3PM, the temperature was 342.2 degrees Celsius.

===========================

Q: Who decided that the thermocouple was broken? Was the manufacturer consulted?
A: TEPCO decided. We have experience in maintenance of the thermocouple. (Matsumoto sounds very testy.)

Q: Is there a possibility of a thermocouple showing temperature lower than what really is and therefore it is broken?
A: If this thermocouple were correct, there would be other thermocouples that would show higher temperature. The other temperatures are trending down. So we think this particular thermocouple is broken.

Q: The temperature rise in early February - was it related to the instrument failure now?
A: We think so. But we didn't know at that time whether it was actually a rise in temperature or the instrument failure. The temperature did go down after increasing the water injection.

Q: How reliable is it to judge "recriticality" by xenon-135?
A: We think it is a reliable indicator.

Q: When was 342.2 degrees Celsius recorded?
A: We finished the testing at 2:54PM. So it must be between that time and 3PM. We'll have to check.

Q: How high did the temperature go? (looking at the graph that was provided)
A: It went overscale, so the graph shows temperatures like that [over 400 degrees Celsius].

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Reactor 2 RPV Bottom Temperature: 94.9 Degrees Celsius at Noon, 2/13/2012

(UPDATE: Instrument deemed broken, as the temperature at 5PM on February 13, 2012 is 275.9 degrees Celsius. It was as high as 342 degrees before 3PM. See my new post.)

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10:00 91.2
11:00 93.7 (from TEPCO's Plant Parameter, 2/13/2012 noon)
12:00 94.9 (Mainichi Shinbun, 2/13/2012, last update 12:57PM)

Mainichi does not have much to say beyond what I've already reported in the posts, here and here. Most certainly it is the instrument failure, TEPCO, NISA say.

The measurement of the temperature at noon must have been disclosed during the press conference held by the Nuclear and Industrial Safety Agency after the TEPCO's press conference. There was no mention of the temperature at noon, as the press conference was brief and was over by 11:30AM.

There are nuclear engineers and experts who doubt this foregone conclusion of "instrument failure". I will write a post about it later once I understand it myself.

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Reactor 2 RPV Bottom 91.2 Degrees Celsius (TEPCO Press Conference 11AM, 2/13/2012 11AM)

(UPDATE 2: Instrument deemed broken, as the temperature at 5PM on February 13, 2012 is 275.9 degrees Celsius. It was as high as 342 degrees before 3PM. See my new post.)

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(UPDATE: 94.9 degrees Celsius as of noon on February 13, 2012. Instrument failure most likely, the company says.)

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The temperature at the bottom of Reactor 2 RPV (69H1):

2/13 5:00 89.6
2/13 (missed the time, I think Matsumoto said 10:00) 91.2

It is not responding to the increased amount of water injected (about 18 tonnes/hour). The temperatures at the other two locations (69H2, 3) are going down. Therefore, it is the instrument failure most likely, TEPCO's Matsumoto concludes.

TEPCO will maintain the amount of water injected for the time being. No plan to change the amount for the time being.

Q: The steady rise of temperature like this doesn't seem like instrument failure.
A: We want to investigate whether such "failure" is possible where the temperature rises in small increments.

Many reporters, hardly any questions, and the press conference is over in less than 30 minutes.

Matsumoto said the temperature may change because they are conducting some test of the instrument.

The temperature data is not yet updated on TEPCO's site.

UPDATE: Hourly temperature at Reactor 2 RPV bottom, latest.

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Reactor 2 RPV Bottom Temperature: 89.6 Degrees Celsius, 5AM on Feb 13

(UPDATE: The latest number is 91.2 degrees Celsius as of 10AM, 2/13/2012.)

==========================

For nearly 18 tonnes/hour water injection, the temperature hasn't dropped a bit. It remains high at 89.6 degrees Celsius at the Pressure Vessel bottom, but we're not supposed to worry. It's all nothing but instrument failure, as TEPCO and NISA have assured us.

From TEPCO's plant parameters, 2/13/2012:

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NISA on Reactor 2 RPV Temperature: Not a Problem

(UPDATE: Latest temperature is 89.6 degrees Celsius as of 5AM, 2/13/2012.)

since it is most likely to be the instrument failure.

Yomiuri Shinbun (2/11/2012):

東京電力福島第一原子力発電所２号機の原子炉圧力容器の底部温度が保安規定で上限と定めた８０度を上回ったことを受け、経済産業省原子力安全・保安院の森山善範原子力災害対策監は１２日夜、臨時の記者会見を開き、「原子炉全体としては冷却されている。放射性物質の放出量にも変化は無く、安全性に問題はない」と述べ、昨年末に政府と東電が宣言した「冷温停止状態」について、変更する必要はないとの認識を示した。

As the temperature at the bottom of Reactor 2 Pressure Vessel at Fukushima I Nuclear Power Plant exceeded 80 degrees Celsius, which is the upper limit in the safety regulations, Yoshinori Moriyama of the Nuclear and Industrial Safety Agency held an ad hoc press conference in the evening of February 12, and said "The reactor as a whole is well cooled. There is no change in the amount of radioactive materials released, and there is no problem with the safety", sharing the agency's view that there was no need to change the status of "cold shutdown state" that the national government and TEPCO had declared at the end of last year.

　保安院によると、複数ある温度計のうち上昇傾向を示しているのは１か所だけで、温度も激しく変化していることから、故障の可能性もあるという。保安院は同日、東電に対し、圧力容器の温度の把握方法や、故障した温度計の保安規定上の取り扱いについて検討し、報告するよう口頭で指示した。

According to NISA, there is only one thermometer among several that shows uptrend and the temperature fluctuates widely, which has led to the speculation that it may be the instrument failure. NISA issued an oral instruction to TEPCO on February 12 to come up with a report to the agency regarding the ways to measure the temperatures of the RPV, and how to handle thermometers that are broken in light of the safety regulations.

Just remember that NISA is staffed with the nuclear and electric power industry people on leave.

In TEPCO's defense, though, the declaration of "cold shutdown state" to the derision of the world (even in Japan, surprise) was made by the prime minister of Japan whose interest seems to be more aligned with the "global" community than with the subjects in the increasingly Orwellian Japan. TEPCO went along with it, for sure.

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(Updated) TEPCO Press Conference on Reactor 2 RPV Temperature

TEPCO's Matsumoto opening remarks:

No Xe-135 detected in the latest gas sampling test.
Preparing to increase water.
1090 kilograms of boric acid solution has been poured into the RPV.

At 2:20PM, the temperature exceeded 80 degrees Celsius.
Since other temperatures at the bottom of the RPV remain low and the temperature of the Containment Vessel is not rising, the cold shutdown state remains.

(There are many reporters this time...)

It's the blue line in the chart (screen capture):

TEPCO thinks it is physically "very difficult" for the temperature to rise above 80 degrees Celsius, and it is likely to be the instrument failure.

No cesium-134 and 137 have been detected, so there is no steam being generated inside the RPV/CV.

Graph generated from the automatic digital reading showing 10 degrees "noise" starting 12 noon (before noon, the noise was 1 degree):

Asahi Shinbun's reporter asked how high exactly the temperature went, as the graph seemed to show the spike above 90 degrees Celsius.

Matsumoto answered the graph is plotting all the 1-second readings from the digital display, not visually verified by the workers. The official reporting is every 6 hours, the reference reporting is every hour.

Q: Will the amount of water be increased if the thermometer at that location continues to rise?
A: We will have to be careful. If the increased water doesn't lower the temperature, the instrument failure will be more likely.

Q: How to verify the instrument failure?
A: We want to do the resistance testing from the central control room.

Q: Why has the temperature started to vary widely since noon?
A: We don't quite know.

Q: When will you get back to the normal operation under the safety regulations?
A: To do it, we have to make sure it is the instrument failure.

Q: Does the instrument failure have to do with the variance?
A: It's not that the instrument failure started today, but it may have started late January when this thermometer started to behave differently from the other two at the bottom of the RPV. The 10 degrees Celsius water is right near the thermometer (15 centimeter away), and the thermometer shows rising temperature. The location of the thermometer should be uniformly cooled.

Q: Where do you measure the temperature of the water injected?
A: The temperature of the water is measured at the buffer tank. No place along the way to get heated.

Q: What happens if the temperature doesn't drop?
A: We will wait and see for a day.

Q: Why did you start mentioning "instrument failure" only when the temperature started to approach 80 degrees Celsius?
A: We didn't think it was behaving erratically. The variance of 1 degrees was understood. The trend changed at the end of January. Also, the temperature remained high as more water accumulate inside the RPV, therefore the instrument failure more likely.

A: We want to see if it is possible to have the instrument failure where the temperature drops, instead of going up.

A: The Containment Vessel is still hot and humid, so we have to make sure the other instruments are working properly. At this point, we don't have better alternatives.

9.9 (core spray, from 6.9) + 7.5 (feed water) = 17.4 tonnes/hour of water is to be injected into the RPV.

Q: Why are you increasing the amount of water if you think it is the instrument failure? What do you think of the safety regulations?
A: We have always informed the NISA and followed the safety regulations. (No answer on why they are increasing water.)

Q: Why did you pick this particular thermometer as the representative temperature for the RPV?
A: Perhaps it was one of the first to come back online last fall, but we will confirm.

Q: What happens if other thermometers fail?
A: We have to think about how to monitor the condition of the reactor, as we cannot enter the Containment Vessel.

(The press conference just finished. The above note is not necessarily comprehensive. In short, TEPCO thinks it is more likely to be the instrument failure, not the actual temperature rising, but it will continue to monitor the situation.)

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JUST IN: #Fukushima Reactor 2 RPV Bottom Temperature at 82 Degrees Celsius

TEPCO's press conference scheduled at 5PM February 12, 2012, Japan Time.

10:00 78.3
11:00 74.9
12:00 79.1

Decision was made at 2:20PM that the the condition of "the temperature at the bottom of the Reactor Pressure Vessel at 80 degrees Celsius and below" was not met; the condition is specified in the safety regulations.

From authoritative source, here's Yomiuri Shinbun.

For more info, see my notes from the 5PM press conference.

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#Fukushima Reactor 2 RPV Temperature: 79.1 Degrees Celsius as of Noon, February 12, 2012

(UPDATE: The temperature exceeded 82 degrees Celsius as of 2:20PM February 12, 2012.)

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Mainichi Shinbun (2/12/2012 1:54PM):

東京電力は１２日、福島第１原発２号機の原子炉圧力容器底部にある温度計の一つが、同日正午現在で７９．１度に達したと発表した。昨年１２月の「冷温停止状態」宣言後で最高値。温度計の誤差を考慮し、８０度を超えると「冷温停止状態」の条件を満たさなくなる。東電は温度計の故障もあり得るとする一方、原子炉への注水量を増やす。

TEPCO announced that one of the thermometers at the bottom of Reactor 2 Pressure Vessel at Fukushima I Nuclear Power Plant was showing 79.1 degrees Celsius as of 12 noon on February 12. It is the highest temperature since the "cold shutdown state" declaration in December 2011. Considering the margin of error, if the temperature exceeds 80 degrees, it would violate the definition of "cold shutdown state". TEPCO thinks the instrument failure is possible, but will increase the amount of water injected into the reactor.

２号機圧力容器下部の温度は２月に入り上昇傾向で、６日午前７時には７３．３度に達した。そのため７日に原子炉への注水量を毎時３立方メートル増の同１３．５立方メートルとし、一時は約６４度まで下がった。しかし再び上昇傾向を示し、１１日午後９時には７３．３度まで上昇。さらに注水量を毎時１立方メートル増やし同１４．６立方メートルにしたが、効果がないため、１２日午後にもさらに毎時約３立方メートル増やす予定。

Temperature at the bottom of the Reactor 2 RPV has been trending up since the beginning of February. It reached 73.3 degrees Celsius at 7AM on February 6. TEPCO increased the amount of water to be injected into the RPV by 3 cubic meters (tonnes)/hour to 13.5 cubic meters/hour on February 7, which lowered the temperature to about 64 degrees Celsius at one time. But the temperature resumed the up-trend, and reached 73.3 degrees Celsius at 9PM on February 11. The company increased the amount of water by 1 cubic meter/hour to 14.6 cubic meters/hour, but so far there hasn't been any effect. The amount will be increased by another 3 cubic meters [to 17.6 cubic meters/hour] in the afternoon.

Other two locations at the bottom of the RPV show the temperatures that continue to go down, in the mid 30s.

Want to bet if TEPCO will say in the evening press conference, "It's instrument failure after all"?

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Just In: Reactor 2 RPV Temperature at 78.3 Degrees Celsius as of 10AM, Feb 12, 2012

From TEPCO's plant parameter - Reactor 2 RPV bottom hourly temperature table (Japanese, for now):

2/11 17:00 69.5
2/11 18:00 71.2
2/11 19:00 71.1
2/11 20:00 70.9
2/11 21:00 73.3
2/11 22:00 72.5
2/11 23:00 71.2
2/12 0:00 71.1
2/12 1:00 69.5
2/12 2:00 71.9
2/12 3:00 74.1
2/12 4:00 75.7
2/12 5:00 74.0
2/12 6:00 74.4
2/12 7:00 76.3
2/12 8:00 74.5
2/12 9:00 77.1
2/12 10:00 78.3 (at TEPCO's morning press conference, 2/12/2012)

2/12 11:00 74.9

TEPCO do not give morning presser on weekends any more, but today is the exception due to the concern over the Reactor 2 RPV temperature. Matsumoto is doing the press conference, instead of the usual junior manager of PR department.

Q: What happens if the temperature here exceeds 80 degrees Celsius?
A: Further increase of water to be injected into the RPV. But the cold shutdown state should take other parameters of the reactor into consideration.

Q: Possible causes?
A: Unstable cooling at the location. Some movement inside RPV of melted fuel, possibly, disturbing the flow of water. We don't think it's likely because we haven't been working near the reactor. Instrument failure is another possibility.

Q: What evidence to verify the accuracy of the thermometer?
A: Difficult.

Q: Containment Vessel's temperature?
A: Dry Well 39.5 degrees Celsius as of 5AM February 12. Other parameters about Reactor 2 is stable, trending down, except for this particular location at the RPV.

A: We're watching out for Xe-135 for any indication of recriticality, so far there is no detection from the gas management system of Reactor 2.

Q: Are municipalities around the plant informed?
A: Yes. We've been informing them of the temperature and the amount of water being injected.

Q: Which is more likely, the unstable water flow or the instrument failure?
A: Not sure. We're on the safety side (that there is actually a rise in temperature), so we're increasing the amount of water.

Q: Current decay heat?
A: We estimate it to be 0.6 megawatt, but we're not sure whether the temperature rise like this is possible, given the uncertainty of how the water flows through the reactor.

74.9 degrees Celsius at 11AM.

Q: Is this the only location that shows abnormality?
A: No abnormal numbers anywhere else.

Q: Amount of boric acid solution to be injected?
A: 1000 kilograms, as before.

Amount of water from feed water system 7.8 tonnes/hour (from 6.8 tonnes/hour), core spray ssytem 10 tonnes/hour.

If the temperature doesn't respond to increased water, then the instrument failure may be suspected.

Q: When are you going to decide on the cause - instrument failure or water flow?
A:

Q: What does the manufacturer of the thermometer say?
A: Nothing so far.

Q: Why is it taking so long to figure out the cause?
A: The problem is that we cannot enter the Containment Vessel. So we do everything we can from outside the CV to figure it out.

(Press conference just ended.)

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Temperature at Reactor 2's RPV Bottom Shoots Up to 75 Degrees Celsius

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):

東京電力は１１日、福島第１原発２号機の原子炉圧力容器底部に３カ所ある温度計のうち、６０度台後半で推移していた温度計が同日夕から再び上昇し始めたため、冷却水の注入量を毎時１トン増やして同１４．６トンとした。同温度計は１１日午後１１時に７４．９度を示す一方、同じ高さにある残り２カ所の温度計は３５度程度で推移しているという。

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.

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#Fukushima I Nuke Plant Reactor 2 RPV Temperature Remains Near 70 Degrees Celsius Despite Increased Water Injection

70.6 degrees Celsius at 5AM on February 9, 67.9 degrees Celsius twelve hours later at 5PM.

TEPCO's thinking on this: It will go down eventually, someday. (Seriously.)

From TEPCO's reference data sheet on Reactor 2 RPV temperatures as of February 9, from February 8:

Let's review the recent events on Reactor 2, a Boiling Water Reactor with Mark 1 containment designed by GE.

In October last year, Quince the robot was sent on a mission to survey the radiation levels in the reactor building. After going all the way to the top floor and measuring 250 millisieverts/hour, it started the descent, and was stuck somewhere between the 5th floor and the 2nd floor after the communication cable was either severed or disconnected. Now, Quince is on a solo mission somewhere in Reactor 2 building to monitor the effect of radiation on electronic equipment.

On January 14, 2012, out of nowhere the temperature at CRD (control rod) Housing spiked to 142 degrees Celsius, only to be plunged to -197 degrees Celsius 5 days later on January 19. TEPCO announced it was an instrument failure. The temperature there spiked above 130 degrees Celsius again in late January, and since then has been dropping down. As of February 9, it is back down to 70s.

On January 19, TEPCO conducted an endoscopy using the industrial endoscope by Olympus to peek inside the structure called Containment Vessel, inside the reactor building. Dozens of carbon-based workers, having trained on Reactor 5, drilled a hole on the CV, inserted the endoscope, and manipulated the endoscope to get the glimpse of the interior of the CV which still contains the Reactor Pressure Vessel (RPV). TEPCO was hoping to find water at about O.P. (Onahama Peil) 6000, which is about the level of the first floor, 5.3 meters from the bottom of the CV. There was no water at that level. Another peek is not scheduled in the near future.

Needless to say, the thermometers at the bottom of the RPV have not been measuring the temperature of water for a very long time, as everybody knows.

Then in February TEPCO announced that the temperature at the bottom of the RPV had been rising since February 2. TEPCO responded by increasing the amount of water injection to the RPV by 50% (from 9 tonnes/hour to 13.5 tonnes/hour) and adding boric acid. Probably as the result of this 50% increase in water, the Reactor 2 sub-drain pit overflowed.

It's not that hard to imagine the decent increase in the amount of contaminated water to be treated.

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Temperature at the Bottom of Reactor 2 RPV Slowly Going Down, For Now

after pumping the largest amount of water since March 11, 2011, the temperature at the RPV bottom went from 72.2 degrees Celsius at 5AM on February 7 to 66.7 degrees at 5AM on February 8.

According to TEPCO's handout for the press on February 7, 2012, TEPCO has been injecting the water at the rate of 13.5 cubic meters (or tonnes)/hour in the Reactor 2 Pressure Vessel:

• The amount of the core spray system injection water was increased from 3.7 m3/h to 6.7 m3/h at 4:24 am on February 7.

• The amount of the continuing feed water system injection is 6.8 m3/h.

On February 1, the total amount of water being injected to the Reactor 2 RPV was 9 cubic meters/hour.

By the way, Mainichi Shinbun reported (2/7/2012) that the margin of error of the thermometers on the RPV may be 20 degrees Celsius:

温度計は事故後、最大２０度の誤差が生じた。東電は冷温停止状態の定義が「圧力容器底部が１００度以下」であることから、誤差を最大に見積もって８０度を超えれば地元自治体に通報すると保安規定で定めている。東電の松本純一原子力・立地本部長代理は６日の記者会見で「炉全体としては十分冷えており、冷温停止状態の判断を見直す必要はない」と話した。

Thermometers exhibited the maximum 20 degrees Celsius error after the March 11, 2011 accident. Since the definition of a cold shutdown state is "to keep the temperature at the bottom of the Reactor Pressure Vessel at 100 degrees Celsius and below", TEPCO's safety regulation specifies that the local municipalities are to be notified when the temperature exceeds 80 degrees Celsius given the maximum margin of error. TEPCO's Matsumoto said in the press conference on February 6, "The reactor is sufficiently cooled, and there is no need to revise the judgment of the cold shutdown state."

So, the current temperature of 66.7 could be as low as 46.7, or as high as 86.7. That's comforting.

The ever-incurious TEPCO and the overseeing agency NISA simply pump more water into the RPV, instead of ever wondering what may be causing the temperature to rise.

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