#Fukushima I Reactor 2: Thermocouples in Containment Vessel Are Acting Up Again

The temperature is either 88 degrees Celsius, or 20 degrees Celsius, depending on which thermocouple you believe.

Or none of the above, and both thermocouples are broken. Given the previous history (from 2012 when one thermocouples after another was failing inside the Containment Vessel of Reactor 2), it is possible that both are broken.

Mainichi Shinbun (4/7/2015) reports:

福島第１原発:２号機格納容器内の温度計が異常な上昇表示

東京電力は７日、福島第１原発２号機格納容器内の温度計が異常値を示したことを明らかにした。

３日午前５時に２０．９度だった温度が同１１時に７０度に急上昇。５日午後５時には８８．５度まで上昇したが、２号機の別の温度計は平常値を示しており、東電は「原子炉の制御に影響はない」として、原因を調べている。

Thermocouple inside the Containment Vessel of Reactor 2 at Fukushima I Nuclear Power Plant shows abnormal rise in temperature

On April 7, TEPCO disclosed that a thermocouple inside the Containment Vessel of Reactor 2 at Fukushima I Nuclear Power Plant showed abnormal temperature.

The temperature was 20.9 degrees Celsius at 5AM on April 3 but it rapidly rose to 70 degrees Celsius at 11AM. On 5PM on April 5 it further rose to 88.5 degrees Celsius. Other thermocouples show normal temperatures. TEPCO says "It does not affect the control of the reactor," and is currently investigating.

Here's the latest temperature parameters for Reactor 2 Containment Vessel from TEPCO's plant parameters page, which omits the particular thermocouple that spiked:

So which thermocouple spiked? It is the thermocouple "supply air D/W cooler(TE-16-114K#1)". There is a site that continues to plot charts from the plant parameter data disclosed by TEPCO, and here's the chart plotting all "supply air D/W cooler" thermocouples:

Looking at the chart, it is more likely that this particular thermocouple broke, and the temperature inside the Containment Vessel remains between 20 and 30 degrees Celsius.

Quickly checking the measuring devices installed inside Reactor 2 (information from TEPCO's site), broken and malfunctioning devices are numerous.

As of July 2014, only 8 thermocouples out of 24 inside Reactor 2 Containment Vessel are monitored in accordance with the safety procedures set by regulatory authorities (meaning only 8 are properly functioning), according to TEPCO's information.

In contrast, 16 thermocouples out of 21 are functioning properly in Reactor 1 Containment Vessel, and all 19 thermocouples are functioning properly in Reactor 3 Containment Vessel.

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#Fukushima I Nuke Plant: TEPCO Managed to Insert a New Thermocouple to Monitor Reactor 2 RPV

There was only one thermocouple left at the bottom of the Pressure Vessel of Reactor 2. Now there are two, greatly enhancing the TEPCO's capability to monitor the "cold shutdown state".

Workers from TEPCO and an affiliate company (most likely Toshiba, who's in charge of probing inside the Containment Vessels of Reactors 2 and 3) finally managed to insert a replacement thermocouple through one of the penetrations on the Containment Vessel of Reactor 2 to 5 centimeters inside the wall of the Reactor Pressure Vessel (RPV).

Of the six thermocouples that monitor the temperature at the bottom of RPV, 5 of them had failed since the start of the accident.

From TEPCO's Photos and Videos (10/3/2012):

It's been a while since TEPCO last announced the details on workers - how many of them, how many teams of workers, what company they belong to, and how much radiation exposure they got from performing the task. This particular work took 2.5 hours, according to TEPCO's handout for the press (in Japanese) of the same day.

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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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4 More Thermocouples May Be Going Bad in Reactor 2 at #Fukushima I Nuke Plant

It looks like four more thermocouples inside the Reactor 2 Containment Vessel are failing:

• return air drywell cooler(TE-16-114A)

• return air drywell cooler(TE-16-114D)

• supply air D/W cooler(TE-16-114F#1)

• supply air D/W cooler(TE-16-114H#1)

The locations of these thermocouples can be (sort of) figured out with this TEPCO document, as of April 25, 2012 (I put the red rectangles around the failing thermocouples):

TEPCO's handout for press, 5/29/2012 lists "Thermometers which indicated large fluctuation". Temperatures have been fluctuating in a meaningful way (increase or decrease in large steps) since May 28 (red rectangles added to indicate the large fluctuations; click on the table for a better image):

But do not worry. TEPCO has a plan to send human workers inside the Reactor 2 building again to somehow install new thermocouples. According to the reference document for the Working Group meeting on May 28, 2012 (pages 10 to 17), the installation work should start sometime in August, after the decontamination of the 1st floor of the Reactor 2 building is complete by mid July. The trial decontamination has already been done by the workers to compare different methods (strippable paint is most effective, so is the radiation shield), and they have just stated the actual decontamination in the environment where the highest radiation level is 4,400 millisieverts/hour (on the surface of the penetration X-34, near the location that TEPCO wants to insert a new thermocouple).

I don't know why there is no robot by now that can do such a work.

Unlike Reactor 4, where carbon-based human workers routinely enter and work in the radiation levels measured in microsievert/hour, Reactors 1, 2 and 3 have much higher radiation levels measured in millisievert or even sievert/hour. Upper floors of Reactors 1, 2 and 3 are too radioactive for human workers, and even the robot (Quince) was left stranded in Reactor 2's 3rd floor because of high radiation that precluded the rescue mission.

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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: Another Thermocouple on Pressure Vessel Dies

Another thermocouple goes kaput on the Reactor 2 Pressure Vessel.

From Jiji Tsushin (4/15/2012):

瞬時に６度上昇、異常と判断＝２号機圧力容器温度計で－東電

Reactor 2 Pressure Vessel thermocouple deemed abnormal after jumping 6 degrees Celsius instantly, says TEPCO

　東京電力は１５日、福島第１原発２号機圧力容器下部に設置された温度計が１４日夜、瞬間的に６．１度の上昇を記録したと発表した。上がり方が異常だったため調査したところ、温度計の電流が流れにくくなっており信頼性に疑問が生じたと判断。１５日未明に監視計器からは外すことを決めた。

TEPCO announced on April 15 that one of the thermocouples installed at the bottom of the Reactor 2 Pressure Vessel at Fukushima I Nuclear Power Plant jumped 6.1 degrees Celsius in an instant on April 14 night. TEPCO investigated, as the rise in temperature was abnormal. The resistance was found to be too high, and on early April 15 TEPCO decided to exclude the thermocouple from the list of instruments that are regularly monitored because there was a doubt on the reliability of the thermocouple.

　東電によると、異常とされた温度計は圧力容器底から高さ約２．９メートルの外壁に設置されており、１４日午後９時ごろ突然、それまでの５３．８度から５９．９度に上昇した。同じ高さにある別の温度計では４５度前後で大きな変化はなかった。

According to TEPCO, the thermocouple in question is installed on the outer wall of the Reactor Pressure Vessel, about 2.9 meters from the bottom of the RPV. At 9PM on April 14, the temperature suddenly jumped from 53.8 degrees Celsius to 59.9 degrees Celsius. The other thermocouple at the same height but at a different position stayed at about 45 degrees Celsius, showing no marked difference.

So, at this location, there will be only one thermocouple monitoring the temperature. Originally there were three, at the measurement location called "vessel wall above bottom head", but the first one, 69H1, died back in February after shooting up above 250 degrees Celsius. Now the second one has died, which must be 69H2, looking at TEPCO's temperature data on Reactor 2:

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1,640 Millisieverts/Hr Radiation in #Fukushima I Nuke Plant Reactor 2 Bldg

When Quince the robot entered the reactor building to measure the radiation levels on the 1st floor of Reactor 2 building, the radiation levels were in 2 digits.

Now, carbon-based colleagues of Quince (TEPCO and Toshiba) entered the same building, and they got to detect 1,640 millisieverts/hour (or 1.64 sievert/hour) radiation on the second floor.

TEPCO and Toshiba employees entered the Reactor 2 building to conduct the survey in preparation for installing the thermometers to replace the current ones that are failing fast. The survey was done on March 15, 16, 21 (this may be Quince only), and 22.

From TEPCO's handout for the press (3/23/2012):

(The first image says "1st floor", but it is "2nd floor".)

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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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Fukushima I Nuke Plant Reactor 2: TEPCO Changes to a Different Thermocouple for Cold Shutdown Assessment, Says No Problem at 30 Degrees Celsius

Kyodo News (2/18/2012):

　福島第１原発２号機で圧力容器底部の温度計が異常な高温を示した問題で、東京電力は１８日、同じ高さにある別の温度計の値を代表的な温度として採用することとし、３０度前後になったと発表した。

Regarding the thermocouple that exhibited abnormal temperatures at the bottom of the Reactor 2 Pressure Vessel at Fukushima I Nuclear Power Plant, TEPCO announced on February 18 that the company had decided to pick another thermocouple at the same height as representing the temperature at the RPV bottom. The official RPV bottom temperature was now about 30 degrees Celsius, the company said.

　東電は「同じ底部にあり、健全性が確認されている」と説明している。

TEPCO explained that "the new thermocouple is also located at the bottom of the RPV, and it has been confirmed to be working".

　圧力容器底部には、容器を囲むように同じ高さに温度計が三つ設置されている。これまで代表点としてきた温度計の数値が２月初めごろから大幅に上昇したため、東電は故障と判断。配線がほぼ断線状態になったとみている。

There are three thermocouples at the bottom of the RPV at the same height, surrounding the RPV. The temperature at the thermocouple that had been used as official temperature gauge for the RPV bottom [of Reactor 2] started to rise sharply in early February. TEPCO has determined that it is the instrument failure in which the wires have been nearly severed.

The new and improved official thermocouple for the RPV bottom is "69H2", as of 5PM on February 17, 2012 when "69H1" exhibiting -3 degrees Celsius was unceremoniously ditched. (See TEPCO's plant parameters for Reactor 2 RPV temperature as of 2/19/2012 11AM.) The ever-incurious TEPCO also stopped measuring the Reactor 2 RPV temperatures every hour.

The temperature at the CRD Housing is now 212.6 degrees Celsius, after it started the steady rise on February 14 from 112 degrees Celsius. Conveniently, the thermocouple there is also suffering the instrument failure.

On the other hand, the temperature at the "RPV Drain Pipe Upper Part" has plunged from about 50 degrees Celsius in mid January to -0.3 degrees Celsius on February 19, but it is not considered the instrument failure.

Nothing to see here, move on, say TEPCO and the government.

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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.

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

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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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