Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[turi]

Cynicism aside, is this not the first public sanction imposed on any member of TEPCO management?

I remember a similar sanction. Possibly when the rat in the power supply incident happened, but I'm not sure.

 

[Cire]

This is not what a "cold shutdown" should look like.

How should a cold shutdown on a reactor that suffered core damage and a hydrogen explosion look like? I feel the plants are in a much more stable condition then one would expect for the amount of damage they took.

 

[zapperzero]

How should a cold shutdown on a reactor that suffered core damage and a hydrogen explosion look like? I feel the plants are in a much more stable condition then one would expect for the amount of damage they took.

Well obviously talking about shutdown, cold or otherwise, when the reactors basically self destructed is just a ridiculous PR tactic.

 

[jim hardy]

Cold shutdown has a specific meaning in US, temperature less than 200F and ~atmospheric pressure..

http://www.nrc.gov/reading-rm/basic-ref/glossary/cold-shutdown.html

As somebody pointed out visible vapor may not indicate active boiling. One can see one's breath on cool days.

Not that it doesn't bear watching, but don't push the 'panic' button just yet.

 

[nikkkom]

Fukushima-Daiichi-Unit-3-July-2013

Looks not that bad.

 

[caldweab]

So, when the news reports that there is a danger of radiation exposure...what exactly is being exposed? I think I know the very basics of the core, which is essentially uranium fuel rods that are bombarded by free neutrons right? Where does Xe, Kr, and I come from? Are these what uranium decays too? When people get radiation sickness/exposure, what is harming them? electromagnetic radiation or something else?

Clearly I have no clue what I'm talking about, but I would like too.

The elements you're asking about are fission products produced from fission reactions inside the reactor ,and honestly the presence of Xe 135 would be a good thing inside the core after the accident since it absorbs neutrons and decreases the fission reactions. Of course this doesn't mean it's good for it to be released to the environment

 

[zapperzero]

Fukushima-Daiichi-Unit-3-July-2013

Looks not that bad.

Doesn't look you could die by simply walking around on that exposed floor for a while. And yet...

Interesting that they've started tearing down some of the adjacecnt buildings. I didn't see that mentioned in any of the plans I read. Perhaps it falls under general rubble clearance.

 

[nikkkom]

Other interesting photos:

http://www.simplyinfo.org/?p=9636

In particular, Unit 4's floor in February 2013.

 

[tsutsuji]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20130727/index.html A sample taken on 26 July 2013 in a trench 50 m away from the sea, on the side of unit 2 was found with 2,350,000,000 Bq/l of cesium. This is a concentration of the same order as the contaminated water that leaked into the sea in April 2011 shortly after the accident. Tepco said that it is possible that this is indeed water that remains from the April 2011 leak, but as other causes are possible, no definitive conclusion can be drawn at this point.

http://www.tepco.co.jp/en/nu/fukushima-np/f1/smp/2013/images/trench02_13072801-e.pdf Analysis Results of Accumulated Water at Unit 2 Seaside Trench in Fukushima Daiichi Nuclear Power Station

http://www3.nhk.or.jp/news/genpatsu-fukushima/20130729/index.html The NRA instructs Tepco to remove the contaminated water from the trench. In May 2013, Tepco started detecting higher contamination concentrations in the sea or in wells near the sea and on 22 July 2013 Tepco admitted for the first time that contaminated water leaked into the sea. The NRA specialists who met on 29 July said there is a possibility that the contaminated water runs through a gravel layer in the ground. Tepco plans to inject chemicals into the gravel layer by September 2013 in order to stop the leak, and to remove the contaminated water in April 2014 or later. However, it is thought that contaminated water from the turbine building, etc. is seeping into the trench, and the development of technology to stop such seepage has not been completed. The storage location after removal has not been decided either. For these reasons, there is no prospect of implementing a radical solution.

 

[etudiant]

The aggregate fuel cesium load in reactors 1-3 at Fukushima was given at about 1600 kg in earlier posts.
Of this, perhaps 4 kg were believed to have vaporized during the explosive phase of the accident.
That suggests that the melted fuel still contains about 400 times the quantity of contaminant as has been released to date.
Cesium is very water soluble and it would be natural to expect the warm coolant water to leach the fuel pellets that were released during the meltdown.
That suggests that the 80,000 plus tons of water in the basements of the reactor and turbine buildings are getting steadily more cesium enriched even as TEPCO is running low on storage space for treated water.
Is something important getting overlooked here or is this a correct understanding of the situation?

 

[etudiant]

The aggregate fuel cesium load in reactors 1-3 at Fukushima was given at about 1600 kg in earlier posts.
Of this, perhaps 4 kg were believed to have vaporized during the explosive phase of the accident.
That suggests that the melted fuel still contains about 400 times the quantity of contaminant as has been released to date.
Cesium is very water soluble and it would be natural to expect the warm coolant water to leach the fuel pellets that were released during the meltdown.
That suggests that the 80,000 plus tons of water in the basements of the reactor and turbine buildings are getting steadily more cesium enriched even as TEPCO is running low on storage space for treated water.
Is something important getting overlooked here or is this a correct understanding of the situation?

 

[nikkkom]

That suggests that the 80,000 plus tons of water in the basements of the reactor and turbine buildings are getting steadily more cesium enriched even as TEPCO is running low on storage space for treated water.
Is something important getting overlooked here or is this a correct understanding of the situation?

I don't think it becomes more contaminated, more like "it remains contaminated". No drastic reduction happens there.

To me it looks like TEPCO has reduced water injection to a minimum it feels comfortable wrt cooling, because it has little space to store this water. This prevents reduction of water contamination.

Two questions I would like to have answers for:

(1) Why TEPCO is not discharging filtered water to the ocean? If the answer is that the water is not clean enough, which nuclides exactly are there?
The background is that at TMI the water was decontaminated enough to be released. All nuclides apart from Tritium were essentially absent, Tritium was present but below the regulatory limit for releases. Yet a lot of people were fighting against releasing it into the river, so TMI operator eventually gave up, brought an evaporator on site and evaporated it all. It took ~2 years, and of course, rabid variety of our beloved environmentalists were still up in arms against it.
Did TEPCO consider using evaporator?

(2) Why TEPCO does not perform active drainage of the ground water? (I suspect the cause is still the same - it has too little space to store it)

 

[etudiant]

TEPCO provided a very helpful summary of the water situation here:
http://www.tepco.co.jp/en/press/corp-com/release/betu13_e/images/130731e0401.pdf
The included flow diagram does show an evaporator to pull down the volume of treated water, but there is close to 300,000 tons of the latter and clearly the evaporator is not keeping pace.
There is no data I've seen on the activity levels of the treated water or of the residual contaminants, possibly including tritium. The zeolite sludge levels are quantified, but not their activities either. They are probably seriously hot.
It is likely, imho, that the basement water is getting more contaminated. There is so little cesium, barely 1 parts per 50,000, that the water cannot possibly be saturated. That implies that the amount dissolved/leached should rise over time. It cannot possibly be helpful to have the entire site soaking in a solution of radioactive cesium with gradually increasing concentration.

 

[nikkkom]

The included flow diagram does show an evaporator to pull down the volume of treated water, but there is close to 300,000 tons of the latter and clearly the evaporator is not keeping pace.

From the diagram it doesn't look like evaporator's output of distilled water fows to the ocean. The arrow on diagram points to "treated water" box. IOW: evaporator is being used to concentrate and remove salts from *circulating* water.

This makes sense, of course, but what actually REMOVES water from the loop? The diagram shows only "Multi-nuclide Removal Equipment" possibly doing it, but it's not unambiguously saying that the water after it is discharged to the ocean.

What is Multi-nuclide Removal Equipment? Is it working? What's its throughput?

It is likely, imho, that the basement water is getting more contaminated. There is so little cesium, barely 1 parts per 50,000, that the water cannot possibly be saturated. That implies that the amount dissolved/leached should rise over time.

The water isn't standing still in the basements.
My understanding is that water is continually pumped out of basements, and a clean-ish water is poured back into containment. With such a scheme, water becomes less salty over time, not more salty.

It is possible that "there is so little cesium, barely 1 parts per 50,000", because the part which could be washed out (i.e. not locked in intact fuel ceramic or solidified melt), has been already washed out.

 

[blab31]

This diagram is regulary published by TEPCO every week since more than a year, and it is a great tool to check the storage volumes and capacities, the volume of contaminated water in Turbine buildings or the amount of water injected in each reactor.

But it also can lead to misunderstand the reality of filtration treatment facilities today :

Multi nuclide Removal Equipment (ALPS) ( http://www.tepco.co.jp/en/nu/fukushima-np/roadmap/images/m120328_01-e.pdf (march 2012) and http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2013/images/handouts_130329_01-e.pdf (march 2013) ) seems like a very efficient facility, it basically removes 62 different nuclides : ratio to the density limit : 4.1E+06 Bq/cm3 before treatment, 6.9E-01 Bq / cm3 after treatment.

But this facility is currently under hot test, only since 2 months or so after manys delays, and they have a lot of issues. One month after the beginning of the test, they found 2 pinholes on a batch treatment tank, then after inspection it was 20 holes.
Three days ago, on 7/29/2013, Tepco reported to Nuclear Regulation Authority that the holes were made by “corrosion”.

In the beginning, the holes were assumed to be made by welding error.
According to Tepco, chloride ion from seawater, hypochlorous acid, Ferric chlorides in the accumulated water corroded the stainless steel.
The facility had been in the test operation only for 2 months.
Due to this leakage, the entire system of ALPS will be suspended until mid September.

As far as nuclide removal is concerned, most of water only runs through cesium absorption facilities (the rest is oil separation and desalination), so yes, cesium concentration after treatment is actually very low and it could be released to the ocean if it was the only nuclide, but for example, Sr-90 concentration is 110 000 Bq/cm3, 3,7 million times the density limit in the water outside the surrounding monitored areas specified by the Reactor Regulation. There is no way they could just dump it in the ocean, so they have to add tanks to store something like 140 000 more tons of water each year. And that's without even trying to lower the water volume in basement of turbine buildings + trenches.

 

[tsutsuji]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20130801/0416_ryushutu.html Tepco is carrying out works to solidify the ground over a 16 m depth along the sea, in order to prevent contaminated water to leak into the sea. However from the start of the work on 8 July 2013 till 31 July 2013, the ground water level on the side of unit 2 rose by one meter as a result of the work. Tepco says that this is because the ground water has been dammed up by the work. As the shallowest layer up to 2 m from ground level is most difficult to solidify, it is feared that ground water will leak through that layer. For that reason, Tepco is studying new countermeasures. The harbour tritium concentration rise is going on, and Tepco is checking the relationship with the ground water rise. NRA president Shunichi Tanaka criticises Tepco saying they have no crisis feeling whatsoever about what is happening. An urgent solution is required.

 

[nikkkom]

This diagram is regulary published by TEPCO every week since more than a year, and it is a great tool to check the storage volumes and capacities, the volume of contaminated water in Turbine buildings or the amount of water injected in each reactor.

But it also can lead to misunderstand the reality of filtration treatment facilities today :

Multi nuclide Removal Equipment (ALPS) ( http://www.tepco.co.jp/en/nu/fukushima-np/roadmap/images/m120328_01-e.pdf (march 2012) and http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2013/images/handouts_130329_01-e.pdf (march 2013) ) seems like a very efficient facility, it basically removes 62 different nuclides : ratio to the density limit : 4.1E+06 Bq/cm3 before treatment, 6.9E-01 Bq / cm3 after treatment.

Sr-90 concentration is 110 000 Bq/cm3, 3,7 million times the density limit in the water outside the surrounding monitored areas specified by the Reactor Regulation. There is no way they could just dump it in the ocean

My layman's ideas of what evaporator is tell me that it would achieve basically the same thing, with much more accessible off-the-shelf technology needed.
Why TEPCO tries to run more complicated ion-exchange system?

 

[etudiant]

My layman's ideas of what evaporator is tell me that it would achieve basically the same thing, with much more accessible off-the-shelf technology needed.
Why TEPCO tries to run more complicated ion-exchange system?

It may be that an evaporator would mobilize some of the nuclides that need to be removed.
The ion exchange system keeps everything dissolved that does not get adsorbed.

 

[Rive]

It is likely, imho, that the basement water is getting more contaminated.

Actually, as I recall the average level of Cs contamination in the water of the basements is lower by two decades than it was at the beginning.

The basements has a serious inflow of (mostly clean) groundwater and also some cooling water is pumped in. This inflows reduces the average concentration. The only input of new Cs is from the corium, amount unknown.

What I'm thinking about: the torus of the reactors seems to be (more or less) intact, without in- or outflow. The stuff inside is still from the very first days... Why don't they try to empty it? They could drastically reduce the torus room radiation level.

 

[zapperzero]

Actually, as I recall the average level of Cs contamination in the water of the basements is lower by two decades than it was at the beginning.

The basements has a serious inflow of (mostly clean) groundwater and also some cooling water is pumped in. This inflows reduces the average concentration. The only input of new Cs is from the corium, amount unknown.

What I'm thinking about: the torus of the reactors seems to be (more or less) intact, without in- or outflow. The stuff inside is still from the very first days... Why don't they try to empty it? They could drastically reduce the torus room radiation level.

Err... there could be corium in there, that is cooled (not so important) and shielded (a bit more important) by water. You might end up increasing the dose rate, iow.
EDIT: although even if you succeeded in decreasing it, I don't see how it would help.

 

[Rive]

Err... there could be corium in there, that is cooled (not so important) and shielded (a bit more important) by water. You might end up increasing the dose rate, iow.
EDIT: although even if you succeeded in decreasing it, I don't see how it would help.

You have a point... Then just replace it with some 'lighter' water?
Eventually they will have to start 'closing the loop' and fix the water flow between the basement of the units and the basement of the turbine buildings.
But right now they can't even go in and look around.

Ps.: I mean, personally.

 

[etudiant]

Actually, as I recall the average level of Cs contamination in the water of the basements is lower by two decades than it was at the beginning.

Thank you, Rive, that is very important data.
TEPCO has processed 500,000 tons of water, while about 100,000 tons are in the facility. So if the cesium contamination now is down to around 1 percent of the original level, that means no substantial additional cesium input from the corium is taking place. Rather reassuring, unless I'm missing something else.

 

[Rive]

Some real data:

At the beginning: http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110327e15.pdf

Later on: http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111214_01-e.pdf

Now: http://www.tepco.co.jp/en/nu/fukushima-np/f1/smp/2013/images/tb_water_130621-e.pdf

 

[nikkkom]

What I'm thinking about: the torus of the reactors seems to be (more or less) intact, without in- or outflow. The stuff inside is still from the very first days... Why don't they try to empty it? They could drastically reduce the torus room radiation level.

I don't think it is known that torus in any of three reactors is watertight.

I think it is safe to assume that any water poured into RPVs eventually flows out into turbine units' basements.

BTW, in addition to my first two questions, here's the third:

(3) Is there any consideration when this water-pouring saga should end? It's been two years and a half, corium's heat output has fallen significantly.

Neither Chernobyl nor TMI employed such a long period of water circulation cooling.

It may make sense to switch to air (or better, nitrogen) injection cooling. For one, this will stop converting NPP into a swamp!

 

[Rive]

(3) Is there any consideration when this water-pouring saga should end? It's been two years and a half, corium's heat output has fallen significantly.

Neither Chernobyl nor TMI employed such a long period of water circulation cooling.

It may make sense to switch to air (or better, nitrogen) injection cooling. For one, this will stop converting NPP into a swamp!

No end on sight. They want to cut shorter the water path, but as I see it in their documents right now it's more a wish than a plan.

If you think about it: a fuel bundle requires three to five years (as I know) underwater before it can be put in a transfer cask (air cooling). However the age of the stuff there already fit for this, the fuel bundle has a specific geometry OK for cooling: the corium doesn't.
So I don't think that they will try for air or nitrogen cooling any soon.

The stuff in Chernobyl is still warm by the way.

 

[etudiant]

(3) Is there any consideration when this water-pouring saga should end? It's been two years and a half, corium's heat output has fallen significantly.

The water injected is recycled plant water, so there is no net addition.
TEPCO is keeping a water processing rate sufficient to ensure the water in the site remains slightly below the surrounding ground water level. The aim is to keep water flowing into the site, rather than have contaminated water flow out. Of course, this is not super effective, given the site goes down close to 100 feet below ground.
Longer term, the ALPS facility ideally can decontaminate about 1000 tons/day, so there is no lack of clean water availability.
Consequently, I think the current water reinjections are aimed more at stabilizing the local ground water flows than at cooling the remaining fuel. Given there are 20 feet of water in the plant already, it is hard to see what incremental cooling a few more inches worth would add.

 

[nikkkom]

The water injected is recycled plant water, so there is no net addition.
TEPCO is keeping a water processing rate sufficient to ensure the water in the site remains slightly below the surrounding ground water level. The aim is to keep water flowing into the site, rather than have contaminated water flow out.

Recent revelations of significantly radioactive ground water levels rising and ground water reaching harbor in significant amounts contradicts this picture. Clearly, water flows out of basements into the ground.

Longer term, the ALPS facility ideally can decontaminate about 1000 tons/day, so there is no lack of clean water availability.
Consequently, I think the current water reinjections are aimed more at stabilizing the local ground water flows than at cooling the remaining fuel. Given there are 20 feet of water in the plant already, it is hard to see what incremental cooling a few more inches worth would add.

I'm confused.
I did not say more water needs to be added.
Water needs to be *removed* (as much as possible).

 

[etudiant]

Recent revelations of significantly radioactive ground water levels rising and ground water reaching harbor in significant amounts contradicts this picture. Clearly, water flows out of basements into the ground.



I'm confused.
I did not say more water needs to be added.
Water needs to be *removed* (as much as possible).

The ground is sufficiently fractured post earthquake that ground water is flowing through the site.
While bedrock is apparently about 150 ft down, none of the seaside barriers go that far, so there is ongoing mixing of groundwater with the seawater. The plan is to keep the water level in the plant steady until barriers can be emplaced to halt the ground water inflow from the higher ground backing the site, probably by freezing the ground to some depth.
In the interim, lowering the water level in the plant is futile and possibly dangerous, as it might uncover dispersed nuclear fuel. So the harbor leakage will in all likelihood continue, fortunately with reduced impact as the plants standing water is now only 1% as radioactive as it was back in March 2011.

 

[nikkkom]

The fuel needs to be uncovered at some point anyway (unless the idea is to keep basements flooded until they crumble into dust). When is that point going to be?

 

[etudiant]

The fuel needs to be uncovered at some point anyway (unless the idea is to keep basements flooded until they crumble into dust). When is that point going to be?

If the roadmaps are to be believed, not for at least 20 years.
There are pretty detailed plans, but they all dissolve into gray mush when you try to get specifics.
We don't know where the fuel is or what shape it is in. The reactors were dry for a long time and overheated hugely, so the fuel may be in powder or in lumps, plus the explosions may have shifted it dramatically. Maybe the fuel fused into the concrete pedestal below the reactor. That would help explain why it does not seem to be adding much contamination to the water, but makes eventual recovery more challenging.
In any case, cleaning up this mess will be a huge engineering task and it is enough if the insides of the facility remain quiescent and the water gets gradually cleaner while the outside debris are cleared away. Once that is done, the real cleanup and fuel extraction can begin.
Imho, the current stage is analogous to debridement in wound care, clearing out the dead and damaged tissue before the actual healing treatment begins.