Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[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?

 

[LabratSR]

http://www.epri.com/abstracts/Pages/ProductAbstract.aspx?ProductId=000000000001025750


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?

Getting close

http://info.ornl.gov/sites/publications/files/Pub37640.pdf

 

[zapperzero]

Getting close

http://info.ornl.gov/sites/publications/files/Pub37640.pdf

hmmm

Using the water injection estimate information by TEPCO, simulations [9,10] generally predict limited core degradation that is later quenched in-vessel. However, the amount of water that made its way to the core region remains a key uncertainty. Decreasing the water injection by half resulted in large-scale core relocation before the end of the simulation. If that simulation were extended, failure of the lower head and melt relocation would likely be predicted

 

[Rive]

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?

No luck for me, too.

Here is a document which is older but has the same person as co-writer:
http://melcor.sandia.gov/docs/Fukushima_SAND_Report_final.pdf

IMHO we won't be able to reach conclusion. Some documents suggests, that for U2 and U3 the actual core status heavily depend on the water amount pumped in by fire trucks: but that water amount will remain unknown.

We have to wait for the next bunch of borescope missions.

 

[nikkkom]

nikkkom

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

Fission fragments are almost exclusively beta and gamma emitters.
Alpha emitters are uranium and transuranics. They are minority contributors to decay heat at this point.

 

[nikkkom]

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.

"After one year, typical spent nuclear fuel generates about 10 kW of decay heat per tonne, decreasing to about 1 kW/t after ten years."

Considering leaching of Cs, let's assume than by now (almost 2.5 years after disaster), every ton of fuel generates 4 kW. Then ~100 tons of fuel in RPV/PCV generate 400 kW. This power can evaporate about 13 tons of water in one day, if no power is lost to ambient.

 

[zapperzero]

So what is your conclusion, nikkkom? Does the corium still need water cooling?

 

[LabratSR]

http://www.epri.com/abstracts/Pages/ProductAbstract.aspx?ProductId=000000000001025750


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?

Clicking on the authors name at that link does take you to this, which references the MELCORE code around page 203

http://prod.sandia.gov/techlib/access-control.cgi/2012/126173.pdf

 

[LabratSR]

Getting closer.

MELCOR Simulations of the Severe Accident at the Fukushima 1F1 Reactor

http://www.fukuleaks.org/web/wp-content/uploads/2013/01/1F1-MELCOR-ANS.pdf

 

[LabratSR]

HaHa!

MELCOR Simulations of the Severe Accident at the Fukushima 1F2 Reactor

http://www.fukuleaks.org/web/wp-content/uploads/2013/01/1F2-MELCOR-ANS.pdf

 

[LabratSR]

MELCOR Simulations of the Severe Accident at the Fukushima 1F3 Reactor

http://www.fukuleaks.org/web/wp-content/uploads/2013/01/1F3-MELCOR-ANS.pdf

 

[nikkkom]

So what is your conclusion, nikkkom? Does the corium still need water cooling?

How much water is pumped in today, 100 tons/day? Isn't that too much?
And then, surprise, there are massive radioactive leaks. Doh...

Forced air cooling may be enough.

 

[Rive]

Forced air cooling may be enough.

For fuel with intact geometry and well planned flow paths - yes.
For the suspected mess - not likely.

 

[jlduh]

Hi,

i have a hard time imagining how the "cooling" works with the injection of the water by Tepco. I mean, nobody knows where the fuel/corium is, but it's very probable that it has relocated outside of the reactor vessel or the containement vessel. It's maybe below the reactor somewhere on or in the basement, and maybe for reactor N°2 somewhere else, in the torus area...

To cool, you need to remove heat, and this is done by a flow of something, in this case of water. But the flow has to be to some degree, to be efficient, in contact with the hot fuel, debris and or corium. Then the question is: how do they manage to create a flow path to reach the hot stuff that is "somewhere" (they don't know where), and probably somewhere down, i mean in a low area which is probably "blind". How then a flow could be created in such an area? I don't know exactly what are the input and ouput point for water circuits on each reactor, but i doubt that the output points can be in places where the flow has REALLY TOUCHED the hot stuff...

Maybe you have some convincing answers and elements that i missed, but really, this supposedly "closed loop" (which is not) water cooling puzzles me...

There might be a flow that cools the hot stuff, but isn't it the groundwater mixed with additional water, with output points that are mainly... leaks to the ocean?

That would explain the increase in contamination in the port, by the way...

 

[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...

The crane was 2 years old it seems (designed to last 20 to 25 years), and went through annual inspection 3 months ago, and daily test. So? Ok, failure can happen. it seems the worst place for it to happen, though...

 

[LabratSR]

Fukushima Technical Evaluation: Phase 1 -- MAAP5 Analysis

http://www.epri.com/abstracts/Pages/ProductAbstract.aspx?ProductId=000000000001025750

 

[nikkkom]

i have a hard time imagining how the "cooling" works with the injection of the water by Tepco. I mean, nobody knows where the fuel/corium is, but it's very probable that it has relocated outside of the reactor vessel or the containement vessel. It's maybe below the reactor somewhere on or in the basement, and maybe for reactor N°2 somewhere else, in the torus area...

To cool, you need to remove heat, and this is done by a flow of something, in this case of water. But the flow has to be to some degree, to be efficient, in contact with the hot fuel, debris and or corium. Then the question is: how do they manage to create a flow path to reach the hot stuff that is "somewhere" (they don't know where), and probably somewhere down, i mean in a low area which is probably "blind". How then a flow could be created in such an area?

Hotter water rises, colder water goes down. Thus, if there is a dense heap of warm corium somewhere down there, water will convect around that, and "smear" thermal energy over the entire water volume. The hotter that lump of corium becomes, the more efficient convention is. In a limiting case, water can boil, and thus ensure that temperature stays below 100 C. However, I think such temps are very improbable today.

TEPCO basically injects water into RPV through some surviving piping, and pumps out somewhat warmer water out of turbine building basement (yes, not even from reactor building basement. Water needs to seep from one to another).

No wonder several *tons* of water manage to escape from such a haphazard cooling loop into the ground.

 

[jlduh]

Yes, convection creates of course a natural flow, but i see in fact the current situation more like some hot fuel, debris and or corium sitting somewhere at the bottom of the big messy pool that the buidings and the basements are in fact now: some convection will occur, but i wouldn't call that a circuit loop... They add fresh water, water gets a bit hotter and they remove blindly some of this water so the temperature stays somewhat constant.

In fact Tepco is injecting water from the top but the soil seem to inject even more from the sides and the bottom, and this is called groundwater flow!

Something interesting here that may create some problems with the plan to pump out groundwater (12 wells) and reject it to ocean before it cools the hot stuff and gets contaminated: it seems the groundwater may be already contaminated BEFORE it hits the reactor buildings, probably because of leaks from the storage tanks...

http://www3.nhk.or.jp/nhkworld/english/news/20130912_02.html

The operator of the crippled Fukushima Daiichi nuclear plant says it has found rising tritium levels at a monitoring well near a wastewater storage tank.

One of the storage tanks leaked more than 300 tons of highly radioactive water in August. The water is likely to have seeped into the soil.

Tokyo Electric Power Company has since increased the number of monitors to check radioactive materials in groundwater near the tank.

The company says the level of radioactive tritium at one of the wells rose to 64,000 becquerels per liter on Tuesday, more than twice the reading the previous day.

The well is located 20 meters north of the leaking tank. Engineers checked soil taken when the well was dug and found beta radiation of 0.1 millisieverts an hour.

Beta rays are kind of radiation emitted from tritium and other substances.

The operator suspects the leak is spreading but says it doesn't know why as the well is not located near to the groundwater flows. It says most of the contaminated soil around the tank has been removed.

The company initially planned to pump up clean groundwater and release it into the ocean before it passes through heavily contaminated reactors buildings. The finding that the groundwater is already tainted before its reaches the buildings may hamper that plan.

Well, as ABE said, no need to worry about contaminated water, it's under control...

 

[nikkkom]

Tritium is yet another red herring here.

Sure, it would be better to not have tritium.
However, the 300000 tons of water in that giant tank farm currently contain far, far worse isotopes (say, Sr-90) in high concentrations. Tritium is almost nothing compared to that.

Yet, again, TEPCO is in a difficult position where even if it would do everything right and would filter all this water to be completely free of all contaminants sans tritium, the usual suspects will scream bloody murder at mere suggestion of releasing this water to the ocean.
"Oh God, horrible tritium with its deadly 18kEv betas! We are all going to die! Evil corporations are killing us!"

 

[a.ua.]

However, the 300000 tons of water in that giant tank farm currently contain far, far worse isotopes (say, Sr-90) in high concentrations.

if you count in this document
http://www.tepco.co.jp/nu/fukushima-np/f1/smp/2013/images/south_discharge_130826-1j.pdf
and given that there strontium 60%. in 全β
Approximately 40 thousand terabecquerels of strontium-90. it is 4 times the release of strontium-90 in the accident at Chernobyl.

Given that strontium is much more mobile and toxic cesium (ingestion) in the future, I think it will be a major problem.

 

[jlduh]

It seems that beyond reality, communication is going to become more important to describe this reality!

TEPCO official: Leakage 'not under control'

A senior official from the Tokyo Electric Power Company has acknowledged that the radioactive water leakage at the crippled Fukushima Daiichi plant is not under control.

The government's top spokesman later said the assessment does not contradict Prime Minister Shinzo Abe's statement, delivered internationally, that the situation in Fukushima is under control.

TEPCO official Kazuhiko Yamashita was speaking at a hearing on Friday in Koriyama City, Fukushima Prefecture. The session was organized by the opposition Democratic Party, with officials from the government and TEPCO taking part.

Yamashita apologized for the radioactive water leaks, saying that what's happening now goes beyond TEPCO's assumptions.
A lawmaker asked if Yamashita agrees with Abe's statement made last Saturday at a general meeting of the International Olympic Committee in Buenos Aires.

Yamashita replied that he believes the current situation is not under control.

Chief Cabinet Secretary Yoshihide Suga later told a news conference that he heard Yamashita made the comment after being pressed several times for an answer.

Suga said government officials have confirmed with TEPCO that Yamashita was speaking in reference to independent incidents, including a leak of radioactive wastewater from a storage tank at the plant.

Suga said that even if such independent incidents take place, multi-layered steps will be taken to prevent the radioactive water from contaminating the ocean.

Suga said it is true that tainted water has leaked from a tank. But he said workers' patrols of storage tanks have been increased from once to 4 times per day, as part of all-out efforts to urgently deal with the problem.

http://www3.nhk.or.jp/nhkworld/english/news/20130913_36.html

And also read his article:
http://ex-skf.blogspot.fr/2013/09/contaminated-water-problems-at.html

And finally, did others here remarked that NHK world has removed since some days the Tag + link that was since the very beginning on the right side (below "Now on air") of their site, directly linking to data from Tepco about Fukushima?

I remarked it was around the date of the Olympic games announcement...

Communication is the way to "present" datas. Is it time to have datas not too visible?