Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[tsutsuji]

If I read correctly, from your document - http://www.tepco.co.jp/nu/fukushima-np/handouts/2013/images/handouts_130820_01-j.pdf - Cs134 is still 46,000 Bq/l and Cs137 100,000 Bq/l, far higher than it should be after cesium removal systems.

You are right. I misinterpreted the NHK article which was merely saying that it is water "after cesium reduction process".

The Japanese press release at http://www.tepco.co.jp/cc/press/2013/1229852_5117.html is consistent with http://www.tepco.co.jp/nu/fukushima-np/handouts/2013/images/handouts_130820_01-j.pdf

I have no idea why Cs concentrations are so high (for example compared with http://www.tepco.co.jp/en/nu/fukushima-np/f1/smp/2013/images/water_130809-e.pdf )

http://mainichi.jp/graph/2013/08/21/20130821k0000m040100000c/001.html Helicopter picture showing workers on the top of the tanks at 05:14 PM on 20 August.

 

[tsutsuji]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20130821/index.html Tank surveillance consisted of patrols twice a day. The tanks are not equipped with water level gauges. This is the fourth leakage event so far, among the 350 tanks.

http://www3.nhk.or.jp/news/genpatsu-fukushima/20130821/2135_kiseii.html After a study group meeting held in the evening of 21 August, the NRA instructs Tepco to equip the tanks with water level gauges and to study alternative storage facilities. The study group will inspect the tanks at Fukushima Daiichi on 23 August.

http://www3.nhk.or.jp/news/genpatsu-fukushima/20130821/2120_jouchu.html Tepco nuclear division top person, vice-president Aizawa will be permanently based in Fukushima. The existence of different people in charge at Fukushima Daiichi, at the Fukushima Daini-based Fukushima Daiichi stabilization center, at the main office and other places had been pointed out as a source of problems as regards information sharing and supervision.

http://www3.nhk.or.jp/news/genpatsu-fukushima/20130821/index.html 6 mSv/hour was measured on the side of the drain 50 m away from the leaking tank, so that one cannot rule out that contaminated water could have flowed into the sea. On 20 August, based on a measurement of the water in the drain finding low radioactive concentrations, Tepco had said there was little probablility that the sea had been contaminated.

 

[zapperzero]

The tanks are not equipped with water level gauges.

Oh my.

By the way, we're not even one full year into the tanks' five-year warranty period and there's already problems. I wonder how it will all look another year on. Can we expect more leaks at least this big?

 

[a.ua.]

I have no idea why Cs concentrations are so high (for example compared with http://www.tepco.co.jp/en/nu/fukushima-np/f1/smp/2013/images/water_130809-e.pdf )

.

Perhaps because of this.

. It has been in use since October 2011.
http://ajw.asahi.com/article/0311disaster/fukushima/AJ201308210065

In those days it was still "hot".

 

[a.ua.]

Oh my.

By the way, we're not even one full year into the tanks' five-year warranty period and there's already problems. I wonder how it will all look another year on. Can we expect more leaks at least this big?

I wonder how radiation affects the rubber packing.?

 

[tsutsuji]

In those days it was still "hot".

The Kurion and Areva facilities were in service.

According to http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110812_01-e.pdf , on 9 August 2011, Kurion and Areva achieved :

Cs 134 = ND (< 1.1 E0 Bq/cm³)
Cs 137 = ND (< 6.8 E-1 Bq/cm³)


See also http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110818_01-e.pdf (17 August 2011)

 

[tsutsuji]

Oh my.

By the way, we're not even one full year into the tanks' five-year warranty period and there's already problems. I wonder how it will all look another year on. Can we expect more leaks at least this big?

Do you have a source for this five-year warranty period ?

 

[tsutsuji]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20130822/2000_genin.html The emptying operation of the leaking tank, by transferring the remaining 700 tons of contaminated water, was completed on 21 August after 09:00 PM. As the radiation is high, Tepco needs to carefully study the inspection method that will be used in order to determine the cause of the leakage. For that reason the inspection is not expected to start before next week.

http://www3.nhk.or.jp/news/genpatsu-fukushima/20130822/index.html Two other tanks were found with respectively 100 mSv/h and 70 mSv/h on their surfaces, but their water levels are normal. It could mean that they incurred leakage in the past.

 

[nikkkom]

I wonder how radiation affects the rubber packing.?

At these levels - probably insignificant.

 

[zapperzero]

Do you have a source for this five-year warranty period ?

I remember reading it somewhere. Perhaps at ex-skf. In short, no.

 

[blab31]

Do you have a source for this five-year warranty period ?

I can't find a tepco release with this information, but it has probably been given during a press conference, because it's all over the news sites, on NHK, or NYTimes here ( http://www.nytimes.com/2013/08/21/w...er-leak-from-japanese-nuclear-plant.html?_r=0 ) "(...)Mr. Ono said that Tepco had assumed the tanks would last at least five years.(...) "

"assuming it will last 5 years" is not exactly a "five-year warranty period", oh well...

 

[tsutsuji]

Thanks, Blab31, for the source.

http://www3.nhk.or.jp/news/genpatsu-fukushima/20130824/index.html Checking past records, Tepco found that when it underwent the water filling test in another part of the plant premises, in July 2011, before being installed at its present location, the tank sunk by about 20 cm into the ground. This event might have caused deformations or damage. However after receiving a report from the contractor company that no problem had been found by an inspection, the tank was dismantled and mounted again at its present location. Two other tanks have a "sunk into ground" record, and although they were checked and found not to be leaking, Tepco has decided to empty them, starting on 25 August. Tepco doesn't know the reason why those 3 tanks sank into the ground during the water filling test.

 

[a.ua.]

with the help of a translator

Fukushima Daiichi nuclear power plant near
Geology and groundwater and analysis

 

[a.ua.]

Any chance of some info about this japanese document regarding installation of permanent monitoring equipment for reactor 2? Again computer translation is not great which is why I ask, but it does sound like the survey revealed problems so they have to think again about this plan?
[/url]

http://www.tepco.co.jp/nu/fukushima-np/roadmap/images/d130829_06-j.pdf
In this document at pages 205-212

* 2 PCV re-survey results.

http://ru.fotoalbum.eu/images1/200905/95064/273731/00000049.JPG

 

[tsutsuji]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20130906/0620_crane.html After 08:30 on 5 September, the arm of a remote-controlled crane that is used to carry out debris removal work at unit 3, bent, and the arm tip fell down.

http://www.tepco.co.jp/nu/fukushima-np/handouts/2013/images/handouts_130905_06-j.pdf Unit 3 large crane jib mast bending and falling

http://www3.nhk.or.jp/news/genpatsu-fukushima/20130905/0422_toudo.html In the middle of October, a frozen soil wall experiment will be started on unit 4 mountain side on a 10 m x 10 m area, freezing the soil over a 30 m depth. The freezing is done by circulating -40 °C calcium chloride in the pipes. The ￥ 1,300,000,000 experiment is planned to be completed within the present fiscal year. The full fledged frozen soil wall is planned to be completed within the next fiscal year.

http://www3.nhk.or.jp/news/genpatsu-fukushima/20130905/index.html Samples taken on 4 September from a well dug 10 m away from the leaked tank were found with 650 Bq/l of all beta. No contamination has been found until now in the groundwater bypass system pumping wells, which are located 100 m downstream.

 

[jlduh]

The video of the falling crane is here:

https://www.youtube.com/watch?v=J_SA3G1X7F4&feature=player_embedded (around 1'33).

Everything is under control at Fukushima, it seems...

 

[Gary7]

Back on page 632 or some such I asked a layman's question regarding melted fuel and received a thoughtful reply regarding the latent heat energy of the fuel - an answer which was over my head. So I'd like to take another stab and ask again in another way; given the two and a half years since the meltdowns of units 1-3 in Fukushima, would the molten (or partially) molten cores still contain enough energy to melt into a liquid mass? Is it an unanswerable question due to the possibility of iron and concrete being subsumed into some of the mass(es)? Is the possibility of re-melt the reason water needs to continually be poured on/into the cores? I recall some discussion about Chernobyl, and I believe the molten core was already solidified within months of the accident - would this be due to it acquiring impurities (concrete, etc..) thus lowering the heat energy?

Just curious because I see a lot of chatter on the fringe sites about corium, most of which seems generated by equal parts fear, paranoia, and ignorance. Any insight would be appreciated. Feel free to move this question to a different thread if it doesn't belong here.

 

[Rive]

... Is it an unanswerable question ...

As far as I know: yes. This question cannot be answered. The temperature of any fragment of the core(s) depends on the heat generated and the heat dissipated. Even (relative) low amount of heat can (re-)melt the stuff, if it's still in one large piece, cornered somewhere with low surface and high mass.

And by the simulations, most (if not all) of the core of U2 and U3 might be 'cornered' in the bottom of the RPVs.

Also, for U1, most of the core might be sunk into the concrete below the RPV (but still inside the PCV). So it's also in one piece.

In Chernobyl, the core mass flown relative large distances and during that absorbed concrete, metals and so, as you wrote: also, it left behind some pieces of the most reactive stuff. So it had high surface (high dissipation).
The basement of that unit worked as an unexpected core catcher.

Ps.: it would be interesting to know if the idea of the 'core catcher' was inspired by those basements in Chernobyl...

 

[nikkkom]

As far as I know: yes. This question cannot be answered. The temperature of any fragment of the core(s) depends on the heat generated and the heat dissipated. Even (relative) low amount of heat can (re-)melt the stuff, if it's still in one large piece, cornered somewhere with low surface and high mass.

You are technically correct: it can't be positively, 100% ruled out that there isn't a single liter of melt in Fukushima's reactors today.
However, it *is* highly unlikely.

 

[Rive]

You are technically correct: it can't be positively, 100% ruled out that there isn't a single liter of melt in Fukushima's reactors today.
However, it *is* highly unlikely.

I agree that it's highly unlikely that any molten corium is present there at this moment.

But as I take it the question was: can it re-melt if the water stopped?

 

[Gary7]

Thank you both for your responses. Very helpful. Yes I was wondering what the likely state of any fuel mass were at this time, considering the degradation of the fuel, the constant immersion in water, and the passage of two years. Part 2 of my question is as Rive mentioned; is the purpose of the continuous flow of water to stop the fuel mass from re-heating into a molten state?

Given the problems created by the daily input of a hundred or so tons of water, at what time will it be prudent to begin reducing the volume of water? My only reference is Chernobyl, and from what I gather, the fuel ceased to be a moving mass fairly early on, and without the addition of so much water as in the case with Fukushima.

So my guess (validated by Rive above) is that the fuel at Fukushima has traveled a shorter distance, indeed may to a significant degree remain inside the RPVs, and therefore has far fewer impurities (concrete, steel, etc...) than what was at Chernobyl, and therefore the decay heat is still high enough to reach the point where it would re-melt were the heat not being continually removed.

This is just a mental exercise; something to think about while reading all the alarmist stuff about china syndromes, which is something I think Arnie Gundersen claimed recently. And there is a lot of nonsense about "where are the cores", which seems to me to be a ridiculous question, and yet one sees it from time to time on certain sites.

 

[Rive]

... and therefore the decay heat is still high enough to reach the point where it would re-melt were the heat not being continually removed.

... and therefore it cannot be ruled out that the decay heat is still high enough that some parts might re-melt...

I think it's also unlikely that it would re-melt at large scale. But I cannot tell... Maybe somebody else can. I don't know.

Anyway, they will keep the cooling and will keep the temperature as it's required to keep the 'cold shutdown'. About Gundersen... I cannot recall: was there any of his claims ever be proven right later on?

 

[a.ua.]

I read, I can not remember where, but it's Japanese sources,
for physical calculations of residual heat
that water can be turned off in 2018.

In addition, in the Chernobyl sarcophagus fuel mass to be at high embrittlement.
Have the fuel dust (30-50 tone as the Chernobyl) is worse than having a fuel slush.

 

[nikkkom]

Given the problems created by the daily input of a hundred or so tons of water, at what time will it be prudent to begin reducing the volume of water? My only reference is Chernobyl, and from what I gather, the fuel ceased to be a moving mass fairly early on, and without the addition of so much water as in the case with Fukushima.

My guess is: TEPCO continues to pour water based largely on paranoia and fear of bad PR. If they stop, fear-mongering idiots from all sides would scream bloody murder.

So my guess (validated by Rive above) is that the fuel at Fukushima has traveled a shorter distance, indeed may to a significant degree remain inside the RPVs, and therefore has far fewer impurities (concrete, steel, etc...) than what was at Chernobyl, and therefore the decay heat is still high enough to reach the point where it would re-melt were the heat not being continually removed.

Total decay heat does not decrease from impurities.

By now, most of decay heat comes from Sr-90, Cs-137, Cs-134. Cs is water soluble, a lot of it had been leached out.

 

[zapperzero]

My guess is: TEPCO continues to pour water based largely on paranoia and fear of bad PR. If they stop, fear-mongering idiots from all sides would scream bloody murder.

I'm getting really really tired of this attitude of yours. A back-of-napkin calculation would show that the corium still needs cooling, especially if it is (as TEPCO assumes) mostly in one piece.

Think you can do better? Fine. Do the work, show the work and THEN call me and a.ua. and others here "fear-mongering idiots". Not before.

 

[a.ua.]

I read, I can not remember where, but it's Japanese sources,
for physical calculations of residual heat
that water can be turned off in 2018

It's Tsutsuji-san translated.

10) Use of PCV fuel debris air-cooling
At present, heat removal of the fuel debris contained in units 1,2,3 reactors and PCVs is done by water cooling by water injection. but in the future, as decay heat diminishes, it is possible to reduce the generation of contaminated water by shifting from water cooling to air cooling.
As additional generation of contaminated water is annulled, contamination reduction can be expected in the buildings where flowing presently occurs (turbine buildings, etc.).

Problems/feasibility:
Securing wind ventilation method;
- For the time being, as the decay heat is high, considerable ventilation power is needed (with the present decay heat, installation is difficult).
- At the earliest, decay heat is expected to become smaller by 2018, but further study is needed so that the air is uniformly blown onto the fuel debris.
Responding to the situation while the fuel is being removed;
- If the PCV has to be filled with water for the purpose of fuel removal, it means that contaminated water has to eventually be generated again, even if temporary air-cooling could be achieved

 

[a.ua.]

Continuing the theme of a former fuel.
Here you can see the continuation of the Japanese

Units[/PLAIN] 1 and 2 and the torus chamber of accumulated water
For analysis of the precipitate

nikkkom

By now, most of decay heat comes from Sr-90, Cs-137, Cs-134. Cs is water soluble, a lot of it had been leached out

It seems to me, the alpha decay generates more heat.
RTG, RITEG

It should produce high energy radiation. Energy release per decay is proportional to power production per mole. Alpha decays in general release about 10 times as much energy as the beta decay of strontium-90 or cesium-137.

All analyzes indicate a low level of alpha nuclides in the "dirty" water
Perhaps the fuel matrix retains the bulk of plutonium and other alpha nuclides.
So it is necessary a long time to cool ...

 

[zapperzero]

\

So my guess (validated by Rive above) is that the fuel at Fukushima has traveled a shorter distance, indeed may to a significant degree remain inside the RPVs,

No. Recent simulations show almost complete cores of 1, 2 and 3 are ex-vessel.

and therefore has far fewer impurities (concrete, steel, etc...) than what was at Chernobyl, and therefore the decay heat is still high enough to reach the point where it would re-melt were the heat not being continually removed.

This is neither here nor there. If the corium has dropped out as simulations show, it has mixed with concrete from the basemat until a sort of thermal equilibrium was reached. It doesn't look anything like Chernobyl, probably. Certainly it has mixed with all the steel in the core and with whatever it found on the bottom of the RPV - mostly the actuators for moderator rods.

And there is a lot of nonsense about "where are the cores", which seems to me to be a ridiculous question

There is almost no doubt they are under the RPVs (although we can't exclude some melt flowing into a torus, I think?).

A better question would be "what shape are the coriums in?". Could be debris bed like at TMI. Could be splatter as if from a big sieve, could be just a big blob or even "lava tubes" or other exotic things we haven't thought of. The answer to this question will come with new remote explorations, I hope.

 

[Rive]

Recent simulations show almost complete cores of 1, 2 and 3 are ex-vessel.

Could you please link me the latest simulation you know about? The one I know about is a bit old. It shows that U1 core is completely ex-vessel, but for U2 and U3 the result is in the edge of in-vessel and partially ex-vessel.

 

[Gary7]

If the corium has dropped out as simulations show, it has mixed with concrete from the basemat until a sort of thermal equilibrium was reached. It doesn't look anything like Chernobyl, probably.

If any of the fuel masses have reached thermal equilibrium, it begs the question of why water continues to be poured onto them. I mean, if the heat needs to be removed otherwise the fuel will re-melt, you can't really call it equilibrium can you? Or, are you saying it has reached equilibrium, its just that the equilibrium temperature is so high that it will still melt steel and concrete?

 

[LabratSR]

This is dated February 2013. Summary on page 75

Enhanced Ex-Vessel Analysis for Fukushima Daiichi Unit 1:

Melt Spreading and Core-Concrete Interaction Analyses with MELTSPREAD and CORQUENCH

http://info.ornl.gov/sites/publications/files/Pub39382.pdf

 

[Rive]

This is dated February 2013. Summary on page 75

Thank you for this one.
It's result not really different from the older ones.

The most through ones I could find previously are:
http://www.nsr.go.jp/archive/nisa/shingikai/700/14/240723/AM-1-1.pdf
http://www.tepco.co.jp/en/nu/fukushima-np/roadmap/images/m120314_02-e.pdf

There was also some less detailed ones from several institutes, but none of them suggests complete ex-vessel status for U2 and U3.

 

[zapperzero]

If any of the fuel masses have reached thermal equilibrium, it begs the question of why water continues to be poured onto them. I mean, if the heat needs to be removed otherwise the fuel will re-melt, you can't really call it equilibrium can you? Or, are you saying it has reached equilibrium, its just that the equilibrium temperature is so high that it will still melt steel and concrete?

I am sorry, I was not using equilibrium in the strict sense of "no heat flow across the boundary". I see how this can cause problems. It's only balanced in that the temperature is constant - as long as there's water flowing through.

 

[hellbet]

Speaking about ORNL study, eight hours after the Fukushima Daiichi Blackout Station, corium (molten fuel) may have melted through RPV then through the containment 7 hours later; that is the full melthrough sequence might be as short as 15 hours timeframe.

Same reactor (Browns Ferry 1 unit), same accident (Blackout Station).

http://web.ornl.gov/info/reports/1981/3445600211884.pdf

Picture is from p. 133 "vertical concrete penetration".

 

[zapperzero]

http://www.epri.com/abstracts/Pages/ProductAbstract.aspx?ProductId=000000000001025750
claims full meltdowns for all three, but you are right, it does not claim specifically that 2 and 3 are ex-vessel

In particular, it states for unit 3:

The types of pressurization transients observed in the 1F3
drywell following RPV depressurization require the addition of energy. This could be
through a relatively rapid but brief dissipation of some of the stored energy in the core debris
or through chemical reactions (for example, oxidation). The simulation of severely degraded
HPCI injection rates at low RPV pressure indicates that one way to generate this type of RPV
pressure transient is through ex-vessel relocation of core debris. However, several
uncertainties related to in-vessel core degradation in a BWR and the impact of salt water on
the core degradation process still remain.

but concludes

The core is
likely significantly damaged and has either relocated almost entirely into the RPV lower plenum
or relocated ex-vessel. These are both reasonable damage conditions based on the available
information.

For unit 2 a core temp progression analysis (indicating complete meltdown at 95 hours) starts on page 220 but there is indeed no mention of ex-vessel.

Oh well. I should learn not to rely on my memory. At all.

EDIT: I can't find this:
MELCOR Simulations of the Severe Accident at the Fukushima 1F2 Reactor
http://www.osti.gov/scitech/biblio/1064358
halp?