Hot reading at reactor blamed on faulty gear

[xchrom]

http://www.japantimes.co.jp/text/nn20120213x1.html

The temperature in the pressure vessel of reactor 2 at the Fukushima No. 1 nuclear power plant exceeded 90 degrees Monday, Tokyo Electric Power Co. said, but discounted the reading as the result of a faulty thermometer.

Two other thermometers at the same height — about 3 meters from the bottom of the pressure vessel — read 33.1 and 32.9 degrees at 10 a.m., while one read 91.2 degrees.

After more water was injected into the reactor at the troubled Fukushima Prefecture plant Sunday afternoon, the two thermometers in accord showed a drop in temperature while "the problematic one has stayed high, so we think it's more likely now that the thermometer is broken rather than the temperature is actually rising," Junichi Matsumoto, a Tepco spokesman, said at a morning news conference.

At 11 a.m. Sunday, the thermometer believed faulty showed a reading of 75.4 degrees, while the two others registered 34.3 and 34.8.

[kristopher]

1. Details of press conference, temp reading up to 345C.

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

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.

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

More at: http://ex-skf.blogspot.com/2012/02/tepco-evening-press-conference-2132012.html

[xchrom]

2. +1

[Yo_Mama]

4. Two possibilities if the other sensors stay low

The first is that the thermocouple is indeed broken. TEPCO was theorizing that the cable is snapped due to the resistance measured.

The second is that a hunk of blobbed fuel came loose and is now blobbed around the thermocouple.

The reason there only seem to be the two possibilities is that you can't have a temp that high so localized (the other temp sensors don't reflect this increase) except in some rare circs. Now if the temps of the other two start rising, the chances are that the fuel configuration has shifted and that cooling is less effective. That's another ball game entirely.

Also, continued monitoring of the gases don't show recriticality of any sort:
http://www.tepco.co.jp/en/press/corp-com/release/12021206-e.html

I would not think a recriticality of any sort is possible now, but then the condition of the fuel is unknown, so it's wise to check.

TEPCO has had multiple failures of the sensors - after all, we are approaching a year of this. This is not the environment these things were designed for, and they will not have a normal operating life.

This is their last regular update:
http://www.tepco.co.jp/en/press/corp-com/release/12021307-e.html

This Japan Times article implies that the other two are still reporting low temps:
http://www.japantimes.co.jp/text/nn20120214a1.html

Note the diagram in that article. If it is right, this sensor is lower down and fuel could be slumped over it, I suppose.

I'd like to know what the other two current readings are!!! If they are rising, the situation is entirely different, no matter what TEPCO says. This Mainichi article says that the other two are stable, which if it is still true is a highly positive sign:
http://mdn.mainichi.jp/mdnnews/news/20120214p2g00m0dm010000c.html

[kristopher]

5. Are you really qualified to say there are only two possibilities?

No one is in a position to say what is happening and there are definitely more potential scenarios than you've imagined.

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



The graph of the thermocouple being tested.



http://ex-skf.blogspot.com/2012/02/reactor-2-rpv-bottom-temperature-at.html

[Yo_Mama]

8. yes, because this little piece of it is a simple system.

That doesn't mean that there are a ton of unknowns, but look at the much more readable document from which that image was taken.

http://www.tepco.co.jp/en/nu/fukushima-np/f1/images/2u_temp2-e.pdf

This has been updated with data from 2/15. Look at where that lower skirt temperature is now. None of the other sensors show the rise in temp.

Either it's broken or it's encapsulated somehow with something hot, so the cooling water doesn't get to it very well. I don't think you can safely assume that it is broken, and the reports of very high temps I am reading here and there don't show up in this doc. The only way it could get to the very high temps reported would be if the very hot stuff were right there.

We are told from the simulations, which are extrapolated from the exposure of the core after the water evaporated, that quite a bit of that fuel melted partway. Without knowing where the sensor is and how big it is I don't know how plausible it is that something could have fallen off the rack and onto it, but it's a decent possibility.

I can't look at those readings and not think that a hunk of junk inside that thing hasn't shifted. That other sensor is also at 0 degree position, so it could be fluxing from partial blockage or it could be fluxing from waste heat. But it's not fluxing much and it's not very hot at all.

Since the official doc doesn't show the very high temps being quoted, I think that the simplest explanation is that something fell off the assembly, and this thing is now in close proximity to a chunk of very hot fuel amalgam. The increase in water feed could account for the cooling which is shown across all sensors.

I'll buy failure of one thermocouple, though I'll be damned if I'll buy the idea that you can just assume that, but the slightly higher temp on other other sensor near that point in the reactor seems to indicate that something really happened. One failure yes. Two failures, no. No wonder NISA's pissed.

[kristopher]

9. Where does the injection of boron fit into your scenarios?

[Yo_Mama]

10. Read this TEPCO statement carefully

http://www.tepco.co.jp/en/press/corp-com/release/12021206-e.html

They injected boron and raised water injection when the temp reading rose above 80 C because of their operational guidelines.

Then they confirmed by testing for gases that there wasn't renewed fission.

After that, as the reading rose they continued to investigate.

The operational guidelines are wise. It's never going to hurt anything to use boron. If something looks different, first apply the safety measures and then investigate.

Their current operational guidelines are that the reactors should be kept in cold shutdown, defined as 100 C. However because of operational uncertainties, they are mandated to keep those temps below 80 C to ensure that the "real" temps are below the 100 degrees Celsius. When the first reading of 82 C was found, that triggered required actions.

For what it is worth, if it had been going recritical they would have detected that in the gas sampling and would have continued injecting boric acid, because they are sluicing tons of water through that thing, so one injection of boric acid isn't going to keep anything under control. But FIRST you apply the safety measure. You do not bobble around waiting for the thing to show clear signs of fission and then try to control it.

NISA got really steamed off by the rapid categorization of the thermocouple as impaired, as well NISA should have. Assuming instrumentation is in error is a major flaming mistake in nuclear reactor operations, because it has contributed to some very bad accidents. That's one highly disturbing thing about this sequence of events.

Then there is the question "what happened?" Something changed. Did something fall over in there when they were mucking around? On February 2nd they changed the water injection rates due to the piping switchover, so it raises issues.
http://www.tepco.co.jp/en/press/corp-com/release/12020205-e.html

[kristopher]

11. Where is the corium?

[kristopher]

3. TEPCO refuses to divulge name of thermocouple manufacturer to reporters

Additional Info on That "Broken" Thermocouple on Reactor 2 RPV
From Yomiuri Shinbun (2/13/2012):

...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.

http://ex-skf.blogspot.com/2012/02/fukushima-i-nuke-plant-additional-info.html

[Throckmorton]

6. As someone who deals with RTD's and Thermocouples all the time,

Tepco's response to the journalists question smacks of the technical arrogance they have exhibited since day one. I routinely consult with manufacturers of these and other devices when one acts up and I can't readily explain the reading that we are seeing or the reason for the failure.

I might see dozens of instrument failures of this type in my career, the manufacturers of the instruments must see that many in a week I’d be willing to bet.

[Yo_Mama]

7. There's an untranslated NISA memo out to TEPCO to measure the temp at the bottom of the reactor

and report back to them by some time on Wednesday.

This will be interesting.

I'm not sure if it is true or not, but the thing was reported to have gone up to 752 C.

What struck me as so odd about this, which may have been due to translation, was that TEPCO seemed to be saying that they were assuming failure. That's not what you are supposed to do in these circumstances.