Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[etudiant]

Given the immediate problems TEPCO has, most notably a near overflowing super contaminated site,
they can be excused for believing that putting this ground water problem on the back burner is justified.
My only question is that this seems to rely pretty much on the idea that the contamination diffuses through the ground water, rather than getting streamed in bulk flows.
Whether that is a safe assumption given that the area has just had a substantial shifting from the quake is not obvious.

 

[Jorge Stolfi]

One thing that I find most disturbing is that TEPCO's knowledge of the state of reactors #1-#3, three months after the accident, is still entirely based on a dozen or so analog instruments, many of them clearly busted. Vital information, like water level and vessel pressure, are being read out from manometers that would look fine on Captain Nemo's control panel.

One would hope that more modern plants have better instrumentation; so that, in case of a severe accident, the operators would be able to tell whether and where the RPV is leaking, whether and to what extent the fuel has been damaged, whether there is corium on the drywell floor, and so on.

However, I suspect that modern plants may be even worse in this regard. Instruments seem to be increasingly based on digital electronics, which may not last long in case of an extended power failure and severe radiation leaks such as those now present at Fukushima. Is this the case?

(They recently found the black box of the Rio-Paris flight that fell in the ocean a while ago. According to the newspapers, the pilots started to climb in order to avoid a storm, but the plane stalled, lost speed and started to fall. They could have recovered easily, but were misled by the intruments. The pitot tubes did register ~100 km/h, but the on-board computer decided that such a low speed was absurd and could only be an instrument failure; it 'censored' that information and displayed a much higher assumed speed to the pilots instead. So they did not understand what was happening until it was too late. In this aspect, it reminds me of TMI...)

So, are we to understand that high radiation at the plant already from the morning of March the 12th made it impossible to send a man to each service floor to check the situation around the pools? Is that a fact or is it hokum? Are we to understand that absent the saving grace of three explosions it would have been impossible to gain 'access' to those pools?

Ming-boggling.

Presumably the regulating bodies will now recommend all exising nuclear plants to be upgraded by installation of redundant automatically triggered HTEDBAFs (Hydrogen Tanks for Emergency Direct Building Access Facilitation) on the service spaces.

 

[sigyn]

Please, are there some data as to oceanic radioactive contamination from Fukushima ? I have not seen anything lately, but I see that the Kuroshio carries to Alaska where McDonalds does get most of the fish fillets.

sigyn

 

[joewein]

One would hope that more modern plants have better instrumentation; so that, in case of a severe accident, the operators would be able to tell whether and where the RPV is leaking, whether and to what extent the fuel has been damaged, whether there is corium on the drywell floor, and so on.

For what it's worth, when the Monju FBR caught fire in 1995, half a year after entering testing, their fire alarm could say there was a fire somewhere in building related to the sodium coolant cycle, but was unable to tell them *where*. By now the Monju FBR may not exactly qualify as "modern", but at least there were already PCs when it was designed.

Presumably the regulating bodies will now recommend all exising nuclear plants to be upgraded by installation of redundant automatically triggered HTEDBAFs (Hydrogen Tanks for Emergency Direct Building Access Facilitation) on the service spaces.

To be fair, at least one pipe to refill the unit 4 pool was only destroyed by the hydrogen explosion. Unit 2 which didn't have its bulding top blown away has always been topped up using the pool cleaning and cooling system, as far as I know.

According to the status reported on the GRS site, on June 16 the unit 4 pool became the last to be switched from the Putzmeister concrete truck pump back to the pool cooling and cleaning system for refilling. They're adding 150 t of water every other day.

 

[etudiant]

Please, are there some data as to oceanic radioactive contamination from Fukushima ? I have not seen anything lately, but I see that the Kuroshio carries to Alaska where McDonalds does get most of the fish fillets.

sigyn

Latest TEPCO data is here: http://www.tepco.co.jp/en/press/corp-com/release/11062008-e.html
The sea report from a Woods Hole Oceanographic cruise off Japan to measure the radiation is here: https://www.whoi.edu/page.do?pid=67796

Note that the TEPCO data is very local, whereas the Woods Hole study is wide area oriented. Unfortunately, it does not appear that there will be any speedy conclusions released from the Woods Hole study, but rather a series of research papers. That may take many months.
That is what we have, it does not really begin to answer your question.

 

[MiceAndMen]

As for access, I think they mean access to spray water.

That was my thought as well. I've certainly been tripped up before by inaccurately parsing English translations of Japanese text. A lot of nuance can be lost in translation, and it doesn't help that a lot of information seems to be ambiguous even in the original Japanese. I've learned, more or less, to wait for further comments or clarification regarding what is being said exactly.

I'm fairly disgusted that the IAEA has chosen to exclude journalists and, by extension, the public from their meeting in Vienna this week with TEPCO and other representatives of various agencies in Japan. In the early weeks before the government took over the press conferences, it was said that the foreign journalists there in Japan were the only ones asking pointed questions or asking for clarification of certain statements. With IAEA's decision to hold this week's talks in secret, we'll no doubt be left with a single narrative when all is said and done, having no chance to pose followup questions or challenge any inconsistencies. That's assuming, of course, that news organizations would have anyone on hand capable of understanding enough of what was being said to ask such questions at an open forum. That is highly doubtful, now that I think about it, so maybe the closed meeting isn't such a travesty after all. On the other hand, it gives the impression that they have something to hide and are gathered in Vienna this week to make sure they all get their stories straight.

As in all things since 11 March, time will tell.

 

[tsutsuji]

http://www.asahi.com/national/update/0621/TKY201106210195.html & http://www3.nhk.or.jp/news/html/20110621/t10013661011000.html : This morning at 7:20 AM a pump that brings water to adjust the concentration of one of the chemicals in the Areva system automatically stopped after detecting the water flow was too high. It was started again in the afternoon after adjusting the water flow.

http://www.asahi.com/national/update/0621/TKY201106210195.html : Only 8 days are left until the storing capacity for contaminated water is full.

http://news.tv-asahi.co.jp/ann/news/web/html/210621016.html : It is expected that a 100 mm rain would result into a 68 mm rise of the water level in the turbine building at unit 2.

http://news.tbs.co.jp/newseye/tbs_newseye4756438.html TEPCO decided to slow down the flow of cooling water at the reactors of unit 1, 2 and 3 by injecting 0.5 to 1 ton per hour less than was previously injected, saying the plant parameters are stable enough.

 

[joewein]

Please, are there some data as to oceanic radioactive contamination from Fukushima ? I have not seen anything lately, but I see that the Kuroshio carries to Alaska where McDonalds does get most of the fish fillets.

The Kuroshio merges with the Oyashio and becomes the North Pacific Current, which crosses the North Pacific from East to West, then splits up and flows down the California coast or up the British Columbia coast / Alaska panhandle. So the Kuroshio does not go to Alaska directly, not all of it heads there and not all that gets there is from the Kuroshio.

I did a quick search on the speed of the current. One study involving buoys and drift nets suggested it would take debris about a year to float across the the North Pacific. The distance for the North Pacific crossing is similar to traveling the US coast to coast twice.

My choice whether or not to eat at McDonald's would be based on factors other than possible traces of cesium in their deep fried fish fillet. I think people are far more likely to die from clogged arteries or diabetes or other health problems than any effects from radioactivity when eating convenience food year after year.

 

[jlduh]

Please, are there some data as to oceanic radioactive contamination from Fukushima ? I have not seen anything lately, but I see that the Kuroshio carries to Alaska where McDonalds does get most of the fish fillets.

sigyn

Radiation is used to keep food safe and free from bacterials, so don't worry, in case of McDonald's this will be an improvement...

 

[MadderDoc]

Has anyone seen a time line of when building radiation levels became too high to allow human entry? <..>

The best bid for a comprehensive timeline that would include this kind of information -- to the extent that the data exists -- would be the Appendix 2 referred to in this page:
http://www.tepco.co.jp/en/press/corp-com/release/11061805-e.html
E.g. for unit 1 it appears to be reported there that an employee on March 12th 11:39 JST entered the building and was exposed to 106.3 mSv (that's the doserate per hour, assumedly). The document is so far unfortunately only available in Japanese.

Alternatively a timeline for the venting procedures could be constructed from the timelines reproduced in the Japanese Government Report to the IAEA -- the venting timing could then be used as proxy for the timing of the release of radioactive contamination to the buildings. A more distant proxy might be produced using data from the radiation monitoring posts around the plant.

 

[GJBRKS]

http://www.asahi.com/national/update/0621/TKY201106210195.html : Only 8 days are left until the storing capacity for contaminated water is full.

The projection has been 7-8 days every day since thursday last week ,
some process variables are not being updated here.

 

[tsutsuji]

http://mainichi.jp/select/weathernews/news/20110621dde001040059000c.html : as part of the solutions implemented to solve the high radiation problem at the Kurion system, tests were performed today setting a three times higher target value for cartridge change.

The projection has been 7-8 days every day since thursday last week ,
some process variables are not being updated here.

They must have been able to decontaminate a few hundred tons, if they were able to run two lines of the purification system for 5 hours the first time, then perform some tests during many more hours. Or perhaps the calculation includes the added capacity of the new tanks that were supposed to be delivered every day or so.

http://news24.jp/articles/2011/06/21/07184912.html : The test which started this afternoon is performed with a 50 ton/hour flow.

 

[MadderDoc]

TEPCO is considering walls to be built into the ground around the plant to isolate the groundwater.

See text and illustrations on page 11 on:
http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110617e4.pdf

It is a well known technique for containing groundwater contamination, but has many failure modes, and very much depends on the implementation and the exact conditions for escape of the contamination through cracks and permeable layers in the underground. As a long term solution it would need supplementing with capping at the surface to avoid further rainwater infiltration -- not readily apparent though how that could be feasible in the case of Fukushima -- and/or a system for pumping up of the contaminated groundwater plume for decontamination -- but, to be sure Tepco does not appear to need more water for decontamination for quite some time yet.

 

[MadderDoc]

Well I for one never was... :-)

that personal opinion apart, discharging radioactive water into the Pacific is not feasible, Corea and China would be raising too harsh protests, maybe if nothing else proves possible they will try with the megafloat as a temporary storage...

it could may be fail later on, but an accident will be in any case more tolerable than a deliberate act...

probably building another more stable facility would have been a safer and more stable option than makeshift containers...

do you think they ruled that out till now because of costs or because of time constraints ?

Catching up to congratulate you for being the poster of the ten thousandth post to this thread!

Thought experiment: If this were my planet, and I had the unfortunate Fukushima moment, would I not eat all shame of having acted so stupidly, then dump the crap in the great sink of the Pacific, get on with living with the consequences, hopefully wiser by the experience ? Would that not be the most rational thing for me to do?

 

[zapperzero]

So, what fact is expressed here? Is it perchance an expression of cause and effect? Or is it an expression of timing of events? The answer is blowing in the wind.

are we to understand that high radiation at the plant already from the morning of March the 12th made it impossible to send a man to each service floor to check the situation around the pools? Is that a fact or is it hokum? Are we to understand that absent the saving grace of three explosions it would have been impossible to gain 'access' to those pools? Access? Exactly what kind of 'access' are we talking about? Access in the sense that one now could (only) look into the pools from a safe distance in a helicopter, what kind of access is that?

Yes I am sure I am overreacting. Calm down old bear.

I've had posts moved to the political thread before, so I'm trying to refrain from commenting on the performance of the various actors. Yes, I think they mean to say it was cause and effect. Something broke in the unit 2 normal venting path because of the unit 3 explosion.

Also, yes, that's the ony reason for which SFPs would have been inaccessible prior to the explosions.

Of special note also, the headcount. According to the report, there were little more than 400 people on site when the earthquake happened, most of them working on unit 4. Fukushima Dai-ichi was running a skeleton crew, for some reason.

 

[MadderDoc]

I've had posts moved to the political thread before, so I'm trying to refrain from commenting on the performance of the various actors. Yes, I think they mean to say it was cause and effect. Something broke in the unit 2 normal venting path because of the unit 3 explosion.

And that is fair dinkum? So, based on the IAEA report are we now allowed, indeed compelled, on this thread to take it as established fact by the highest nuclear authority that the unit 3 explosion rendered a unit 2 valve inoperable? Which valve, btw -- the statement of inoperability of 'the valve' makes reference to the previous statement, in which reference is made to two different valves. I think you get my drift, a reader of a technical document is not supposed to need to interpret the text as were it poetry.

 

[tsutsuji]

http://www.zakzak.co.jp/society/domestic/news/20110621/dms1106211654023-n1.htm : The Japan Meteorological Agency announced that the tsuyu rain season had begun today in the Tohoku region (which comprises 6 prefectures in the North-East of Japan, including Fukushima prefecture). For Fukushima prefecture, this is 9 days later than an average year. Heavy rains pouring 30 mm per hour were deemed possible today in the region.[PLAIN]http://www.jma.go.jp/en/radame/imgs/prec/205/201106211530-00.png
Rain map from http://www.jma.go.jp/en/radame/index.html?areaCode=205

 

[zapperzero]

And that is fair dinkum? So, based on the IAEA report are we now allowed, indeed compelled, on this thread to take it as established fact by the highest nuclear authority that the unit 3 explosion rendered a unit 2 valve inoperable? Which valve, btw -- the statement of inoperability of 'the valve' makes reference to the previous statement, in which reference is made to two different valves. I think you get my drift, a reader of a technical document is not supposed to need to interpret the text as were it poetry.

I'll take a stab at interpreting the poetry. AFAIR, units 2 and 3 vent through the same stack and there is a Y junction. I'm going to go out on a limb here and say that the unit 3 blast jammed shut a valve that is on the Unit 2 side of that junction, outside the reactor building and that operators may or may not have succeeded in venting into the #2 reactor building.

 

[Jorge Stolfi]

To be fair, at least one pipe to refill the unit 4 pool was only destroyed by the hydrogen explosion. Unit 2 which didn't have its bulding top blown away has always been topped up using the pool cleaning and cooling system, as far as I know. According to the status reported on the GRS site, on June 16 the unit 4 pool became the last to be switched from the Putzmeister concrete truck pump back to the pool cooling and cleaning system for refilling. They're adding 150 t of water every other day.

If there had been no explosion, would it have been possible to activate the #3 SFP cooling equipment? The primary containment of #3 seems to be leaking into the (former) service space, so if the building had not exploded it would have been filled with radioactive steam from the top down, through the fuel chute and stairwells.

In contrasts, the leak of #2's primary containment seems to be in the suppression chamber, right? So the escaping steam is perhaps being scrubbed, with most its radioactivity going into the basement water rather than into the building's atmosphere. If that is true, then, without the explosion of #3, the contamination inside it could have been worse than that in #2. Does this make sense?

 

[MadderDoc]

I'll take a stab at interpreting the poetry. AFAIR, units 2 and 3 vent through the same stack and there is a Y junction. I'm going to go out on a limb here and say that the unit 3 blast jammed shut a valve that is on the Unit 2 side of that junction, outside the reactor building and that operators may or may not have succeeded in venting into the #2 reactor building.

Well. a) Unit 2 and 3 do not vent through the same stack. b) to be consistent with the Japanese Government report to the IAEA, the inoperable valve in question would be one of the S/C side valves, i.e. a valve deep down in the bowels of the beast, in the basement floor of unit 2.

 

[zapperzero]

If there had been no explosion, would it have been possible to activate the #3 SFP cooling equipment? The primary containment of #3 seems to be leaking into the (former) service space, so if the building had not exploded it would have been filled with radioactive steam from the top down, through the fuel chute and stairwells.

There's water in the basement, too. Corium may be there as well. What matter, if it gets filled top-down or bottom-up? Is it somehow better that a larger fraction of radioactive steam may be released into the atmosphere, as compared to Unit 2?!

 

[zapperzero]

Well. a) Unit 2 and 3 do not vent through the same stack. b) to be consistent with the Japanese Government report to the IAEA, the inoperable vent in question would be one of the S/C side valves, i.e. a valve deep down in the bowels of the beast, in the basement floor of unit 2.

Well then I don't understand

 

[SteveElbows]

Well. a) Unit 2 and 3 do not vent through the same stack. b) to be consistent with the Japanese Government report to the IAEA, the inoperable valve in question would be one of the S/C side valves, i.e. a valve deep down in the bowels of the beast, in the basement floor of unit 2.

I went looking for which technical document I had seen which suggested explosion at 3 caused problems at 2. I did not find very much in the documents sent to IAEA. But I found something in the last report TEPCO did, which I think is only in Japanese so far:

http://www.tepco.co.jp/cc/press/betu11_j/images/110618l.pdf

Unfortunately I think that computer translation of this document is perhaps not good enough for this discussion, so I wait for a better translation. If anyone wants to have a go, try page 27 of that document.

 

[Jorge Stolfi]

There's water in the basement, too. Corium may be there as well. What matter, if it gets filled top-down or bottom-up? Is it somehow better that a larger fraction of radioactive steam may be released into the atmosphere, as compared to Unit 2?!

Sorry for my confused prose. I meant to say that the steam leaking from #2's containment may be cleaner than that leaking from #3, because #2's may be going through the suppression pool scrubber, while #3's seems to be going straight into the service space through the refueling pool. So, without the explosion, #3 may have been more off-limits than #2.

 

[MadderDoc]

If there had been no explosion, would it have been possible to activate the #3 SFP cooling equipment?

I think ultimately yes, but not right away, there might be some non-standard electrical repair needed. As the narrative is being sketched out before us, unit 3 is the bad guy contributing in some fashion to the demise of both unit 2 and unit 4. Swallowing that, if unit 3 had not exploded things might've developed in a much more benevolent direction.

The primary containment of #3 seems to be leaking into the (former) service space, so if the building had not exploded it would have been filled with radioactive steam from the top down, through the fuel chute and stairwells.

Fair enough, but there are caveats: this is assuming that the leaking was not caused by the explosion. It also assumes that the observed steam leaking is from containment vessel water, and not more trivially, water leaking from the sfp and into the hot space above the reactor and the containment vessel.

In contrasts, the leak of #2's primary containment seems to be in the suppression chamber, right? So the escaping steam is perhaps being scrubbed, with most its radioactivity going into the basement water rather than into the building's atmosphere. If that is true, then, without the explosion of #3, the contamination inside it could have been worse than that in #2. Does this make sense?

It does, and with the caveats above, it's plausible.

 

[zapperzero]

Sorry for my confused prose. I meant to say that the steam leaking from #2's containment may be cleaner than that leaking from #3, because #2's may be going through the suppression pool scrubber, while #3's seems to be going straight into the service space through the refueling pool. So, without the explosion, #3 may have been more off-limits than #2.

No, sorry for MY confused prose.

I meant there is undoubtedly contaminated water in unit #3 basement and it is undoubtedly giving off radioactive steam which is contaminating the lower levels.

 

[MadderDoc]

I went looking for which technical document I had seen which suggested explosion at 3 caused problems at 2. I did not find very much in the documents sent to IAEA. But I found something in the last report TEPCO did, which I think is only in Japanese so far:

http://www.tepco.co.jp/cc/press/betu11_j/images/110618l.pdf

Unfortunately I think that computer translation of this document is perhaps not good enough for this discussion, so I wait for a better translation. If anyone wants to have a go, try page 27 of that document.

Thanks Steve, perhaps this is where it's coming from, whatever it is. I agree the machine translation is probably not good enough to decide what that is, but it seems clear at least that in the timeline for unit 2 in this document, all reference to the unit 3 explosion has not been omitted. This is unlike the unit 2 timeline reproduced in the appendix to the Japanese government report to the IAEA, which in comparison appears to have been scrubbed of reference to unit 3. Otherwise, the two timelines appear to be quite similar at about this time between March 13th and 14th.

 

[MadderDoc]

Considering the recent abduction of our only decent explanation of the observed heat signature in thermographs from the unit 4 reactor pit (=the explanation that hot water was leaking from sfp to pit), I feel I have a pebble in my shoe.

I previously posted a mapping of the contents of the pool -- based on the two videos from the SFP4 -- showing the number of racks to be fairly close to an early estimate of the number of assemblies in storage in the pool, and that gave me some confidence that I had 'seen them all'.

Already then some other posters said they felt that estimate was too low, that it probably did not include the newly removed core assemblies. I did look at the video data again, and could find possible room in the blind angles for a few extra racks, but certainly not enough to hold a full core load -- and left the question there -- on the impression that there was sufficient uncertainty about the actual number of assemblies to not necessarily produce an overt inconsistency between the mapped rackspace and the estimated range of the number of assemblies.

However, ever since, it's been the higher estimate of the number of assemblies in the pool that has kept popping up, also in data released directly by Tepco, and consequently my confidence in having seen them all during the mapping of SFP4 has eroded. Otoh, I still can't see where the extra assemblies could be hiding in the pool. I would be happy to have my results corroborated or rejected by another mapping attempt made independently from my own. Absent that, I must say that I cannot exclude based on my mapping that some assemblies may still be in the reactor pit.

 

[joewein]

Sorry for my confused prose. I meant to say that the steam leaking from #2's containment may be cleaner than that leaking from #3, because #2's may be going through the suppression pool scrubber, while #3's seems to be going straight into the service space through the refueling pool. So, without the explosion, #3 may have been more off-limits than #2.

When I calculated the amounts of cesium in the ~105,000 t of water in TEPCO's data sheet (reactor basements, turbine basements, trenches and rad waste buildings, but not in SPFs), I was amazed at the comparison of the units:

• 1/2 of the cesium is in unit 2 alone
• Another 1/4 of the total is in the central rad waste building, but was mostly pumped out of the #2 basement and trench.
• Almost all of the rest is in unit 3.
• A little more than 1% is in unit 1
• About 0.1 % is in unit 4

That means:

• Unit 2 was 3x as dirty as unit 3
• Unit 3 is 50% bigger and 30x as dirty by volume as unit 1

I can understand why the water in #2 is much dirtier if the gas has been scrubbed through S/C water. But why is #3 so much dirtier than #1, when #1 melted down at a much hotter stage (after only 5 hours), when its isolation condenser was barely effective while the core isolation cooling system in #3 kept injecting water for 3 days or so?

I guess it must all be a function of the pressure before venting and its effects on the containment...

 

[zapperzero]

• Unit 2 was 3x as dirty as unit 3
• Unit 3 is 50% bigger and 30x as dirty by volume as unit 1

I can understand why the water in #2 is much dirtier if the gas has been scrubbed through S/C water. But why is #3 so much dirtier than #1, when #1 melted down at a much hotter stage (after only 5 hours), when its isolation condenser was barely effective while the core isolation cooling system in #3 kept injecting water for 3 days or so?

Well, Unit 3 is much bigger than Unit 1 in terms of installed capacity (460 vs. 780 MWe), so that could be a factor as well.

 

[SteveElbows]

However, ever since, it's been the higher estimate of the number of assemblies in the pool that has kept popping up, also in data released directly by Tepco, and consequently my confidence in having seen them all during the mapping of SFP4 has eroded. Otoh, I still can't see where the extra assemblies could be hiding in the pool. I would be happy to have my results corroborated or rejected by another mapping attempt made independently from my own. Absent that, I must say that I cannot exclude based on my mapping that some assemblies may still be in the reactor pit.

The temperatures shown on the thermal images were not generally very high really. So I am not really sure that we have clear signs of a big source of heat in the reactor area, but I admit some of the thermal images still interest me in this regard. Is it possible that we are just looking at the heat of steam that has blown in a northerly direction as it rises up from the pool? Or we are looking at water that is in the pit & reactor well area, but is not really very hot?

I have trouble imagining some fuel still being in reactor area, because diagram from the other day that showed work to inject water into reactor well & pit areas, seems to suggest that the core shroud has been removed and placed in the pit. I don't imagine them having any fuel in the area if shroud has been removed. It would be helpful if we knew more about the exact stage the shroud replacement work was at when disaster struck.

 

[SteveElbows]

Thanks Steve, perhaps this is where it's coming from, whatever it is. I agree the machine translation is probably not good enough to decide what that is, but it seems clear at least that in the timeline for unit 2 in this document, all reference to the unit 3 explosion has not been omitted. This is unlike the unit 2 timeline reproduced in the appendix to the Japanese government report to the IAEA, which in comparison appears to have been scrubbed of reference to unit 3. Otherwise, the two timelines appear to be quite similar at about this time between March 13th and 14th.

While we are waiting for full translation, here are some interesting press stories based on the document:

http://www.yomiuri.co.jp/dy/national/T110619002601.htm

http://search.japantimes.co.jp/cgi-bin/nn20110619x2.html

There are some interesting details covered by these stories, including the venting problem and some other things that went wrong as a result of explosions.

 

[zapperzero]

The temperatures shown on the thermal images were not generally very high really. So I am not really sure that we have clear signs of a big source of heat in the reactor area, but I admit some of the thermal images still interest me in this regard. Is it possible that we are just looking at the heat of steam that has blown in a northerly direction as it rises up from the pool? Or we are looking at water that is in the pit & reactor well area, but is not really very hot?

It could even be heat from nuclides in the RPV walls and shroud, for all we know.

 

[SteveElbows]

It could even be heat from nuclides in the RPV walls and shroud, for all we know.

Any ideas how we learn more about this issue in theory? I have no proper sense in my mind of how much heat something like the shroud may create months after shutdown.

 

[zapperzero]

Any ideas how we learn more about this issue in theory? I have no proper sense in my mind of how much heat something like the shroud may create months after shutdown.

I'm under the impression that some of the posters here may have first-hand experience with such issues...