A thermometer of Reactor 2 indicates 89℃ / Reaching 100℃ in 4.7 days at this rate

Following up this article.. Thermometer of Reactor 2 indicates rapid increase in temperature again / 79℃ on 5/10/2015 [URL]


The temperature indicated by the thermometer is still rising at 2.3 ℃ per day in Reactor 2.

From the end of April to mid May, the temperature indicated increased by 35℃, which has been in the constant increasing trend.

At 23:00 of 5/14/2015, it reached nearly 89℃. If it keeps increasing at this rate, it would reach 100 ℃ in 4.7 days.

The latest parameter shows a slight decrease lasting for 6 hours. It is not known what is occurring inside of PCV (Primary Containment Vessel) of Reactor 2 but Tepco has not made any announcement on this.


2 A thermometer of Reactor 2 indicates 89℃ : Reaching 100℃ in 4.7 days at this rate








Français :

Un thermomètre du réacteur 2 est à 89 °C : à ce rythme il sera à 100 °C dans 4,7 jours


Article lié : Un thermomètre du réacteur 2 indique à nouveau une augmentation rapide de la température : 79 ℃ le 10 mai 2015

Dans le réacteur 2, la température indiquée par le thermomètre augmente toujours de 2,3 ℃ par jour.

De fin avril à mi-mai, la température indiquée est montée de 35 ℃, ceci de façon continue.

Elle était pratiquement de 89 °C le 14 mai à 23:00. Si elle continue d’augmenter à ce rythme, les 100 ℃ seront atteints dans 4,7 jours.

Les derniers relevés montrent une légère baisse depuis 6 heures. On ne sait pas ce qui se passe dans la PCV2 (Primary Containment Vessel of Reactor 2 = Enceinte de confinement primaire du réacteur 2) et Tepco n’a fait aucun communiqué là-dessus.

2 A thermometer of Reactor 2 indicates 89℃ : Reaching 100℃ in 4.7 days at this rate


  1. Alarm bells should be ringing across Japan. Temperatures greater than 100 degrees will cause steam which means uncontrolled atmospheric radiation releases. At 89 degrees it’s likely that substantial amounts of highly contaminated water vapour are already being released. What is the cause of the temperature increase – recriticality? Why is the mass media ignoring this?

  2. No, what should be going on is a little thing called critical thinking.

    The first thing you ask yourself is, “what are the other temperature sensors reading?”

    If they all show an increase then it’s probably real. If they all show no change and only this one is changing then you likely have a radiation damaged sensor.

    Guess what? All the other temperature sensors show no change.

    1. Nuclear logic: When temperatures go down we have achieved cold shutdown. When they go up our equipment is faulty.

    2. By all means let’s have critical thinking.

      You argue that if the other sensors are showing no change then the readings from this one must be faulty.

      What makes you confident that the temperature must be uniform throughout the PCV?

      If the temperature is bound to be uniform, why have Tepco installed an array of sensors at different locations?

      If the sensor is faulty, why is Tepco still reporting its readings?

      1. Those four sharp dips in the rising slope seem intriguing too.
        First three about a day apart, except for the latest. Can barely see the first.

        A reminder by Diemos (s’il vous plait) of non-radiation & radiation environment failure modes might be of interest to rule out at least most of those. What possibilities remain might offer a narrower view towards enlightenment of that particular location.

        Is it a 2, 3, or 4-wire thermal probe though?

        Am out of time tonite (correction: this AM) to find Fukushima-Diary article of thermocouple map(s). Perhaps Mr. Hawes might agree to help.

        Thank you, gentlemen.

        1. I’m also out of time tonight (it is indeed night here) and unfortunately I can’t read Japanese. However I’d be very interested to learn more about the location of all the sensors and possible explanations for the rises and dips in the one we’re discussing. The indicated temperature has been declining fairly steadily since May 14 but there was another ‘dip’ on the way down – unlikely to be a statistical artefact because earlier parts of the curve appear highly uniform. It could all, pace Diemos, be the result of faulty equipment, but if it’s not then it’s surely extremely important to know the cause of these (apparently local) temperature fluctuations.

          Here are some links re thermocouples:

          http //fukushima-diary.com/2013/01/tepco-cant-disclose-the-circuit-diagram-of-the-issued-thermometer-in-reactor2-for-saving-intellectual-property-of-toshiba/

          http //fukushima-diary.com/2012/02/heating-gauge-was-lost/

          http //fukushima-diary.com/2012/02/fukushima-worker-suspects-the-heating-gauge-is-not-broken/

          1. … and here’s a better link

            http //ex-skf.blogspot.com/2015/04/fukushima-i-reactor-2-thermocouples-in.html

      2. Tepco’s site does not report its reading. There a different site that takes TEPCO’s raw data and plots it.

        Which lead to an interesting conundrum. If one of your sensors goes bad do you;

        a) Keep reporting its values and have everyone start howling that the reactor is melting down.


        b) Stop reporting its values and have everyone start howling that TEPCO is engaging in a coverup.

        1. a) The reactor has long since melted down.

          b) There is ample evidence that Tepco routinely engages in coverups.

          1. Yes, reactors 1, 2 and 3 melted down 4 years ago and spewed a bunch of contamination into the environment.

            Since then the cores have been congealed blobs somewhere lower than they used to be and contamination has continued to dribble out of the site.

            So, why … exactly … do you say “Alarm bells should be ringing across Japan” because a thermocouple went bad?

            1. I do not accept your claim that the cores are congealed blobs. Given that explosions occurred, parts of the cores could be splattered over the walls of the PCV, stuck in pipes…we do not know.

              Re your claim that Tepco’s site does not report its readings – it clearly does report the readings, as evidenced by the tepco.co.jp link at the end of Iori’s article. Note that the temperatures have been going down for some days now. Faulty sensor or local heat anomaly?

              Why should alarms bells be ringing? – because there is no certainty that the sensor is faulty and because evidence that temperatures may be rising, and at risk of exceeding 100C, implies (a) there may be a risk of recriticality and (b) there may be a heightened risk of releases of (highly) radioactive steam.

              Apologies for the typo in my last entry.

            2. I would have hoped to have seen an argument formulated & documented to show that the thermal sensor is indeed defective. Perhaps you were a little short on time yourself.

              We don’t see any obvious failure modes that i’m familiar with in the above graph, do we?

              Perhaps another “black box” problem may offer another opportunity to find and discuss facts, as commentary will sadly shortly disappear here.

              I do appreciate that you are both willing to discuss the matter in a non-ad-homenim manner, and I thank you both for participating!

              1. There is still at least a couple of days to add comment here, by the way.

                Would it be telling if recent 131I detections had occurred?

                1. Detection of short-lived fission products at the site would be a clear signal of criticality.

                  Detection of short-lived fission products at the site with spikes in the temperature sensors and “Alarm bells should be ringing across Japan.”

                  Detection of I-131 in sewage sludge without detection at the site is a sign of medical patients undergoing radioactive iodine therapy excreting I-131 into the sewers.

                  I-131 has not been detected at the site.

              2. The sign of failure is odd readings in one sensor without odd readings in the redundant sensors. That’s why you put in redundant sensors.

              3. http //www.omega.com/temperature/z/pdf/z021-032.pdf

                Here’s a primer on how thermocouples work and how they can go bad.

                In this environment my first guess would be either degradation of the wire insulation from radiation or corrosion of the wire.

        2. In other words Tepco’s dilemma is whether to conceal the facts or risk being accused of once again concealing the facts. Poor Tepco.

  3. http //fukuichi.mods.jp/?p=20%2C21%2C22%2C23%2C24&fname=p02.csv&cnt=10000&update=更新

    A plot of all the redundant sensors using data going back several years.

    From the title of the plot you can see that these are measuring the temperature of the outside air coming into the heat exchanger.

    Here’s a plot of the temperature of the air coming out of the heat exchanger:

    http //fukuichi.mods.jp/?p=15%2C16%2C17%2C18%2C19&fname=p02.csv&cnt=10000&update=更新

  4. http ://fukushima-diary.com/wp-content/uploads/2015/05/2-A-thermometer-of-Reactor-2-indicates-89%E2%84%83-Reaching-100%E2%84%83-in-4.7-days-at-this-rate.png
    http ://fukushima-diary.com/wp-content/uploads/2015/05/Thermometer-of-Reactor-2-indicates-rapid-increase-in-temperature-again-79%E2%84%83-on-5102015.png

    For reference, both listed as “SUPPLY AIR D/W COOLER HVH2-16E(TE-16-114K#1) in upper left corner of graphs.

    Quote: “The parameter is updated every 6 hours. This thermometer is installed in PCV (Primary Containment Vessel) of Reactor 2, and it is not considered to be out of order.”
    http ://fukushima-diary.com/2015/05/thermometer-of-reactor-2-indicates-rapid-increase-in-temperature-again-79%E2%84%83-on-5102015/

    Quote: “From Tepco’s credibility review of thermometers, the issued thermometer is still supposed to be used for “reference”.
    They observed an abnormal change in the indicated temperature, however they could not conclude it is out of order.”
    http ://fukushima-diary.com/2015/04/a-thermometer-of-reactor-2-indicates-a-rapid-increase-of-temperature-from-20%E2%84%83-to-70%E2%84%83-within-6-hours/

    Quote: “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 …”
    http ://ex-skf.blogspot.ca/2015/04/fukushima-i-reactor-2-thermocouples-in.html

    Quote: “Tepco defined they were “broken”, but the indicated temperatures are showing the relationship with the volume of coolant water.”
    … “In the press conference of 1/23/2013, journalist Oshidori inquired Tepco for the circuit diagram of the thermocouple of the indicator so we can look into if the thermometers are really disordered, what is the actual state etc.”
    http ://fukushima-diary.com/2013/01/tepco-cant-disclose-the-circuit-diagram-of-the-issued-thermometer-in-reactor2-for-saving-intellectual-property-of-toshiba/

    http ://fukushima-diary.com/2013/01/reactor2-temperature-started-decreasing-since-the-volume-of-injection-water-was-increased/

    Quote: “Reactor 2 marked 93.7℃ at 2/13/2012 11:00, but it went to 276.4℃ at 17:00.
    Tepco is asserting the heating gauge is broken.
    The heating gauge is thermocouple, Tepco tried to check resistance but immediately after the test, the heating gauge indicating 276.4℃. The resistance was about 500Ω. Tepco is asserting the wire is nearly broken.
    The reason why it was broken is not known. The meter is not indicating error message.”
    http ://fukushima-diary.com/2012/02/heating-gauge-was-lost/

    Quote: “Actual Fukushima worker, Happy20790 suspects the heating gauge is not broken.”
    … “ハッピー @Happy20790″ …”Source” https ://twitter.com/#!/Happy20790/status/168681701357273088
    … ” Even if it’s true that the heating gauge is broken, we can’t fix it, and what if other 2 gauges got broken too ? I don’t think it’s broken though. I don’t know the distance of the nuclear debris and heating gauge, nor the flow of cooling water but I think it’s likely that only one part gets heated.”
    … ” and even if it’s actually broken again, I don’t know how it can be broken but breaking wire or problem of a terminal makes it indicate maximum + or – in case of thermocouple thermometer. It can’t be noise either. I wonder if Tepco will try to repro agian..”
    http ://fukushima-diary.com/2012/02/fukushima-worker-suspects-the-heating-gauge-is-not-broken/

    Remember the muon imaging?
    http ://fukushima-diary.com/2015/03/nagoya-uni-significantly-small-amount-of-fuel-remaining-in-reactor-2-no-announcement-about-underground-situation/

    Reference & contrast to http ://2.bp.blogspot.com/-Ez0vYBjnibo/VSTd2QmmX1I/AAAAAAAAHaQ/xFE8k63oDHo/s1600/R2CVTemp4-7-2015TEPCO-2.jpg please. No alignment markings seem obvious to me, so am uncertain which way is North in any image.

    Redundancy implies two or more sensors in one distinct location. 15~21 appear to be in the same bore hole, according to that diagram. All “O” thermocouples appear very near each “bundle”. Are they anywhere near the red blob in that image?

    Some real data on those thermocouples would be helpful now (without divulging Toshiba IP), IMHO. Are they two, three or four wire thermal sensors? A note on which metals are used to form the bimetal would be interesting, as well as the material used for insulation.

    It often seems one finds a whole universe within any topic, and we are just scratching the surface here.

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This website updates the latest news about the Fukushima nuclear plant and also archives the past news from 2011. Because it's always updated and added live, articles, categories and the tags are not necessarily fitted in the latest format.
I am the writer of this website. About page remains in 2014. This is because my memory about 311 was clearer than now, 2023, and I think it can have a historical value. Now I'm living in Romania with 3 cats as an independent data scientist.
Actually, nothing has progressed in the plant since 2011. We still don't even know what is going on inside. They must keep cooling the crippled reactors by water, but additionally groundwater keeps flowing into the reactor buildings from the broken parts. This is why highly contaminated water is always produced more than it can circulate. Tepco is planning to officially discharge this water to the Pacific but Tritium is still remaining in it. They dilute this with seawater so that it is legally safe, but scientifically the same amount of radioactive tritium is contained. They say it is safe to discharge, but none of them have drunk it.


May 2015