Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[Rive]

And so we get to ask another round of questions.
The measured dose rate decreases with height, which makes zero sense to me. Any ideas?

If the models are correct then there are only a relative small amount of core debris still in the RPV and the rest, slumped down to the slump pit on the bottom of the PCV (and even lower than that as it burned some hole in the concrete) is shielded by water.

So for first look it looks OK for me.

Ps.: can't wait for the water sample. The low dose measured in the water can indicate that the corium has little direct connection with the cooling water.

 

[rmattila]

Ps.: can't wait for the water sample. The low dose measured in the water can indicate that the corium has little direct connection with the cooling water.

Or that a year-and-a-half of flushing with fresh water has washed away most of the water-soluble substances and only the less soluble material remains in place.

 

[Cire]

Or that a year-and-a-half of flushing with fresh water has washed away most of the water-soluble substances and only the less soluble material remains in place.

Or most of the core is still in the bottom of the RPV

 

[Rive]

Or most of the core is still in the bottom of the RPV

That would be a miracle... For the other two cores the models are not necessarily suggests the RPV-damage, but for unit 1...

Or that a year-and-a-half of flushing with fresh water has washed away most of the water-soluble substances and only the less soluble material remains in place.

I wonder if flushing through the turuses would reduce the radiation levels in the basements?
The contamination of the water in the basements are continuously falling, but the toruses are most likely still full with the stuff from the first days.

 

[Astronuc]

What would be found in the torus would have to be mostly insoluble. The radioactivity decreases with time, or otherwise the radionuclides have been transported either to collection systems or to the environment.

http://www.world-nuclear-news.org/RS-Unit_1_containment_vessel_investigated-1110124.html

An investigation is underway into the internal conditions of the primary containment vessel (PCV) of the reactor at unit 1 at the damaged Fukushima Daiichi nuclear power plant. Tokyo Electric Power Company (Tepco) said that the water level in the vessel has been found to be higher than previously estimated.

An investigation is underway into the internal conditions of the primary containment vessel (PCV) of the reactor at unit 1 at the damaged Fukushima Daiichi nuclear power plant. Tokyo Electric Power Company (Tepco) said that the water level in the vessel has been found to be higher than previously estimated.

Some retrospective - old news

http://eetd-seminars.lbl.gov/sites/eetd-seminars.lbl.gov/files/Fukushima1_Technical_Perspective_LBL_EEDT_04052011-1.pdf

 

[a.ua.]

.

Ps.: can't wait for the water sample. The low dose measured in the water can indicate that the corium has little direct connection with the cooling water.

Analysis Result of the Accumulated Water in Unit 1 PCV
at Fukushima Daiichi Nuclear Power Station

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_121012_02-e.pdf

 

[MikeIt]

Just a guess but shiny metal in the drywell could be mirror insulation. There's a fair amount of it. It's not out of the realm of possibility that the dynamic forces that resulted from the breach of the RPV by core debris also tore up some of this insulation and deposited some of it where the picture shows.

 

[tsutsuji]

24 September 2012 government-Tokyo Electric mid and long term response committee, steering committee (10th meeting)

3-2 Treatment of accumulated water
http://www.meti.go.jp/earthquake/nuclear/pdf/120924/120924_01n.pdf Ground water bypass action plan

1) Previous related topics:
https://www.physicsforums.com/showthread.php?p=3882136#post3882136 23 April 2012 Plan to reduce volumes of groundwater seeping into units 1~4 buildings by groundwater bypass
http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_120618_05-e.pdf 18 June 2012 Progress status of ground water bypass


2) Translation:

As pages 08/11 to 11/11 happen to be copies of older presentation, I translate only the new materials found on pages 01-07 :

01/11

 

[tsutsuji]

2) Translation:

02/11

03/11

04/11

 

[tsutsuji]

2) Translation:

05/11

06/11

07/11

 

[tsutsuji]

24 September 2012 government-Tokyo Electric mid and long term response committee, steering committee (10th meeting)

3-6 Preparations for fuel debris removal
http://www.meti.go.jp/earthquake/nuclear/pdf/120924/120924_01ee.pdf Survey of accumulated water inside unit 1 reactor building triangle corners

Translation:

01/06

02/06

03/06

 

[tsutsuji]

Translation:

04/06

05/06

06/06

 

[zapperzero]

So the idea, if I understand it right, is to lower the local water table level to that of the water inside the reactors?

 

[rmattila]

So the idea, if I understand it right, is to lower the local water table level to that of the water inside the reactors?

The idea is to enable lowering the water level inside the buildings (and ultimately to pump them dry) without causing an increase in the groundwater inflow.

 

[Rive]

The idea is to enable lowering the water level inside the buildings (and ultimately to pump them dry) without causing an increase in the groundwater inflow.

So they are meant to keep the inflow?

 

[zapperzero]

Have you guys seen this?

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_121015_01-e.pdf

One of the pictures shows what appears to be part of an empty rack.

 

[Cire]

So they are meant to keep the inflow?

You want just enough inflow so you know contaminants are not flowing out. But not so much inflow that your pumps can't keep up.

 

[tsutsuji]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20121017/index.html On 17 October, the NRA launched a new "Special Nuclear Facility Monitoring and Assessment Committee" composed of nuclear safety experts including Fukushima prefecture related persons, whose purpose is to continuously monitor Fukushima Daiichi's decommissioning.

http://www3.nhk.or.jp/news/genpatsu-fukushima/20121016/index.html The Nuclear Regulation Agency [an administrative body below the NRA] launched its bureau located in Fukushima prefecture Hirono town, where they borrow a soccer-related facility. It shall deal with Daiichi's decommissioning (8 people) and also the Fukushima Daini nuclear power plant (6 people).

http://www3.nhk.or.jp/news/genpatsu-fukushima/20121016/1725_hairo.html The Chiba Institute of Technology - which developed Quince - has presented a new robot, called "Sakura", designed for Fukushima Daiichi. With a 50 cm height it is about 2/3 of the size of the older generation. As replacing the batteries of a contaminated robot takes too much time, it is rechargeable. The Institute said they would like to have it start being used at Fukushima Daiichi by the end of this year.

http://www.nedo.go.jp/news/press/AA5_100156.html Sakura related press release. The other item, called HAL, is a robot suit with a radiation shield, a cooling system, and a biological data monitoring system (such as body temperature, heart pulsation) (for human beings to carry) (for nuclear disasters in general, not specifically for Fukushima Daiichi).

 

[Cire]

Some good reading:

http://www.new.ans.org/pubs/journals/nt/a_14634

Summary and opinion: http://atomicinsights.com/2012/10/oak-ridge-researchers-prove-fukushima-unit-4-spent-fuel-pool-never-a-danger.html#more-13073

 

[etudiant]

The paper mentioned here: http://www.new.ans.org/pubs/journals/nt/a_14634
is unfortunately behind a paywall, but the second reference from Atomic Insights does provide the meat of the paper.
The paper shows quite clearly that left entirely to itself, the Reactor 4 SPF and its contents would have reached equilibrium around 90*C, well below the boiling point, with enough water present to keep the fuel covered for at least 13 days.
So NRC Chairman Jaczko's comments to the contrary were wrong.
In Jaczko's defense, there had been a big quake and several explosions, suggesting leaks were possible, plus the Reagan had encountered a massive nuclear plume, so that SPF was a reasonable source of concern.
What is surprising is that with three reactors having had explosions, the NRC heads concern should focus on the SPF of the only reactor left unfuelled at the time of the accident.

 

[zapperzero]

What is surprising is that with three reactors having had explosions, the NRC heads concern should focus on the SPF of the only reactor left unfuelled at the time of the accident.

I seem to remember the #4 SFP was making the most heat, as it contains the most recently-extracted fuel, but I may be wrong.

 

[Rive]

The paper shows quite clearly that left entirely to itself, the Reactor 4 SPF and its contents would have reached equilibrium around 90*C, well below the boiling point, with enough water present to keep the fuel covered for at least 13 days.

Without knowing the whole paper and the used models I cannot be sure, but if the equilibrium of the pool was around 90*C, then for me it definitely suggest that around some hot fuel bundles there was boiling.

90 -> 100*C temperature change with natural convection means a very limited cooling.

I have some serious doubts.

 

[Hiddencamper]

Without knowing the whole paper and the used models I cannot be sure, but if the equilibrium of the pool was around 90*C, then for me it definitely suggest that around some hot fuel bundles there was boiling.

90 -> 100*C temperature change with natural convection means a very limited cooling.

I have some serious doubts.

In the US, we assume boiling begins at 200F, or about 93C. I agree that 90C suggests localized boiling was happening as 90C was probably a bulk temperature and not localized, and as we know (and can be seen in PWRs), localized boiling can happen in various amounts as you approach boiling points.

Now I do know that it takes a few days for boiling to start in a normal SFP, additionally unit 4 had a much large water inventory to work with because the separator gate was out and the reactor was opened up. 13 days before full boiloff is possible, but some more specific data would be needed. Its likely boiling started within 4-5 days (full core decay heat load at 90 days since reactor shutdown for that mass of water).

I do know that spent fuel pools with a 1/3rd core offload (on their own) will BEGIN boiling in <72 hours, but the time to complete the boiloff takes longer than the time to start boil off (due to latent energy of water).

 

[tsutsuji]

Without knowing the whole paper and the used models I cannot be sure, but if the equilibrium of the pool was around 90*C, then for me it definitely suggest that around some hot fuel bundles there was boiling.

90 -> 100*C temperature change with natural convection means a very limited cooling.

I have some serious doubts.

If the mean temperature value is 90°C and if some parts are reaching 100°C, it means that other parts are lower than 90°C. Then, those colder parts would generate less steam. Are you sure that all in all the steam quantities are much different than when you use the simple model where all parts have the same temperature ?

Also, wouldn't the steam bubbles generated in the hot spot condensate before reaching the pool's surface ?

 

[Cire]

Don't forget that the pressure at the fuel bundles isn't atmospheric due to their depth. The boiling temperature is going to be a few degrees higher at that location. There will also be fairly significant thermals moving through the bundles.

 

[jmelson]

I seem to remember the #4 SFP was making the most heat, as it contains the most recently-extracted fuel, but I may be wrong.

I believe this is correct, fuel from the #4 reactor had been removed and placed in the
pool a couple months (?) before the earthquake, to prepare for major work in the reactor
vessel before refueling. Also, the pool was loaded with the fresh fuel to go in after the
work was complete.

Jon

 

[etudiant]

Without having seen the actual paper, the summary suggested that the SPF water temperature would rise over a period, but that the equilibrium for heat loss from evaporation versus decay heat from the stored fuel was slightly below 90*C, 87*C by the researcher's etimates.
That overall thermal balance would of course include hot spots around the more recently used fuel, so localized boiling with subsequent quenching of the steam bubbles would be a reasonable expectation.

 

[rmattila]

While the difference between 90 and 100 Celsius probably does not have a significant effect on the fuel cooling conditions, it may have an important effect on the fuel pool liner stresses. I don't know if the Fukushima pools were rated for 100 C, but I know that there are pools in some (European) plants dimensioned to withstand with certainty only about 85 C.

 

[Burnsys]

Is this report true?

http://www.agoracosmopolitan.com/news/nature/2012/10/19/4621.html

Mitsuhei Murata, who served his country as Ambassador to both Senegal and Switzerland, explained in a recent interview that far from the situation at the Fukushima Daiitsu plant improving, it is actually worsening in an alarming way: the ground beneath the plant's number 4 reactor is sinking. Mr Murata implied that the whole structure is on the verge of collapse. He wrote to the Secretary General of the United Nations stating unequivocally that the fate, not only of Japan, but of the rest of the world depends on the No. 4 reactor.

 

[tsutsuji]

http://www.iaea.org/newscenter/focus/fukushima/statusreport280912.pdf Fukushima Daiichi Status Report, 28 September 2012 (A summary of the latest information provided by Tepco)

Is this report true?

http://www.agoracosmopolitan.com/news/nature/2012/10/19/4621.html

Mitsuhei Murata, who served his country as Ambassador to both Senegal and Switzerland, explained in a recent interview that far from the situation at the Fukushima Daiitsu plant improving, it is actually worsening in an alarming way: the ground beneath the plant's number 4 reactor is sinking. Mr Murata implied that the whole structure is on the verge of collapse. He wrote to the Secretary General of the United Nations stating unequivocally that the fate, not only of Japan, but of the rest of the world depends on the No. 4 reactor.

One of Tepco's replies to such fears is available at http://www.tepco.co.jp/en/nu/fukushima-np/info/12062901-e.html (29 June 2012)

See also the following:

http://www3.nhk.or.jp/news/genpatsu-fukushima/20120831/0450_4gouki.html Tepco has completed a new report on unit 4's earthquake resistance, taking into account the most recent findings on wall bulge etc. and the fact that as a consequence of removing the debris on the upper floors, the mass of the building was reduced by 4700 tons. The conclusion is the same as in the May 2011 report: the building can withstand [Japan Meteorological Agency] intensity 6 earthquakes.

http://www.tepco.co.jp/en/press/corp-com/release/2012/1217413_1870.html The new seismic safety report

Also, that the whole Fukushima coast sunk by some 60 cm (and moved by 2.4 m Eastwards) during the 11 March 2011 earthquake is not the same as saying that unit 4 or anything else is still sinking now.

http://en.wikipedia.org/wiki/2011_earthquake_and_tsunami#Geophysical_effects "A 400 km (250 mi) stretch of coastline dropped vertically by 0.6 m (2.0 ft), allowing the tsunami to travel farther and faster onto land"

See also http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_120413_04-e.pdf "Water level measurement in order to confirm the soundness of the Unit 4 Reactor Building" (13 April 2012)