Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[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.

 

[nikkkom]

The plan to keep basements flooded for a decade doesn't sound good to me.
Everything metallic will rust through for sure; what about concrete in the foundations? Is it designed to be stable in permanently wet state?

 

[etudiant]

The plan to keep basements flooded for a decade doesn't sound good to me.
Everything metallic will rust through for sure; what about concrete in the foundations? Is it designed to be stable in permanently wet state?

The long term stability of the structure is clearly a concern, but as with everything else about this disaster, it is uncharted territory. There have been recommendations to block the flow of groundwater into the facility by creating a deep barrier of frozen ground uphill from the site.
That might then allow the site to be drained, as the fuel will also be cool enough for dry storage in a few more years. Unfortunately, the site is still murderously radioactive and likely to stay that way for decades, so until the robotics industry steps up its game, it is probably safer to leave the place submerged.

 

[nikkkom]

The long term stability of the structure is clearly a concern, but as with everything else about this disaster, it is uncharted territory.

Not sure about it. The history of Chernobyl could provide quite a number of lessons.

 

[Rive]

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.

It's a bit more difficult.

There is a groundwater level around the unit/turbine building, and there is another around the main seawater pumps near the harbor (which level is lower).

The water level of the turbine buildings is kept lower than the local groundwater level, which causes a massive inflow. This inflow prevents the groundwater contamination around the turbine building and increases the water amount stored in the site.

However, there are some 'forgotten' power cable trenches between the turbine buildings and the main seawater pumps. These trenches are filled with water from the turbine building. And the water level of these trenches - which is ~ the same as in the turbine building - is clearly higher than the groundwater level around the seawater pumps. This causes an outflow there.

Actually, they are halfway with the solution. The groundwater bypass - once becomes operational - will reduce the groundwater level around the turbine building: so they can reduce the water level in the buildings (and in the trenches) and still keep the inflow in the turbine building.

Also, they made some drilling and chemical injections/solidification near the harbor: this is already started to raise the groundwater level there (around the seawater pumps).

Once/if the groundwater level around the pumps becomes higher than in the trench, they win.

If it's not possible or they can't make it, then they will have to freeze those trenches (but as it seems now, nothing else).

 

[tsutsuji]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20130806/0800_kumiage.html After solifidying the ground in the area along the sea, the ground water level started rising and it is feared that it has started overflowing and pouring into the sea. Tepco was planning to start pumping up that ground water at the end of this month, but after receiving instructions from the NRA to start as soon as possible, it is starting this week to dig small wells and to pump up water. The water will be temporarily stored in an underground facility, and later it will be stored in the storage tanks within the plant premises. Between July 31 and August 5, in the measurement wells on the side of unit 2, cesium concentration rose 14-fold, and all beta (including strontium) rose 46-fold. Tepco doesn't know the reason for the rise and is researching the details of the cause. Now, two years and 4 months after the accident, the concrete situation and the spreading of consequences of contaminated water outflows are still unknown, and responses are following each other like searching one's way in the dark with one's hand.

http://www.tepco.co.jp/en/nu/fukushima-np/f1/smp/2013/images/2tb-east_13080502-e.pdf Detailed Analysis Results in the Port of Fukushima Daiichi NPS, around Discharge Channel and Bank Protection Underground Water Obtained at Bank Protection, 5 August 2013

 

[turi]

They had a look at the Unit 2 PCV on 2nd of August but weren't able to gather as much information as they wanted. They should have retried it today:
http://210.250.6.22/en/nu/fukushima-np/handouts/2013/images/handouts_130731_09-e.pdf

 

[tsutsuji]

http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2013/images/handouts_130807_07-e.pdf (7 August 2013) Draining Plan between the Water Intake Channel of Unit 1 and Unit 2 at Fukushima Daiichi Nuclear Power Station


http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2013/images/handouts_130722_07-e.pdf (22 July 2013, 47 pages, English) Increases in the Concentration of Radioactive Materials in Seawater and Groundwater on the Ocean Side of the Site: Current Situation and Countermeasures

A summary:

http://www3.nhk.or.jp/news/genpatsu-fukushima/20130803/index.html (3 August 2013) The NRA has set up a new working group dedicated to the contaminated water outflow into the sea. It had its first meeting on 2 August 2013. It admitted that it is feared that the ground water has already overflowed over the solidified ground layer, as the water level rose. As a countermeasure, they announced a plan to install new equipments called "catch basins", and to start pumping up water at the end of this month. Opinions were voiced such as the opinion that the countermeasures must be taken more quickly than planned and the opinion that the ground water flow must be analysed in detail. The NRA has set up another working group whose task is to analyse the spreading of radioactive substances that poured into the sea and to assess the consequences on the environment. Tepco estimates the tritium released into the sea from May 2011 to July 2013 to be between 20,000,000,000,000 and 40,000,000,000,000 Bq. This is about the same amount as the yearly release that is allowed under the regulations for the plant under normal operation. As regards cesium and strontium, it will take more time to produce an estimate because this requires analysing the underground migrations.

< The contaminated ground water problem >

Ground water containing radioactive substances are a problem in the area where Fukushima Daiichi units 1,2,3 and 4 are located.

From north to south, units 1,2,3 and 4 are located in a row.

Each unit consists, from the mountain side to the sea side, of a reactor building and a turbine building, and between there and the sea there are a number of ramified underground tunnels called "torenchi" in Japanese (from the English "trench"), inside which seawater intake pipes or electric cables are passing.

The ground water containing highly concentrated radioactive substances is mainly accumulated inside the turbine building basements or inside the trenches, but it is thought that some of it has seeped out into the surrounding ground.

(a) The seawater brought by the tsunami (b) water that has been in direct contact with the meltdown fuel (c) ground water flowing from the mountain side. These are the components of the large quantities of contaminated water containing radioactive substances released by the accidents.

The trigger of the problem is the detection of highly concentrated radioactive substances in ground water measurement wells on the sea side near unit 2 in May 2013.

In particular, the tritium concentration had risen, reaching a value 10 times higher than the value measured in a survey performed at the end of 2012.

The tritium concentration in the sea water in the harbour had also risen.

In July 2013, after it was understood that since April the ground water in the well had been moving up and down in coupling with the sea water level, Tepco admitted that contaminated ground water was pouring into the sea.

Tepco and the NRA hold a few considerations concerning the contamination of the ground water.

First, shortly after the accident in April 2011, when contaminated water poured into the sea in the vicinity of unit 2's water intake, some of this water spread underground, so that it is possible that it is detected in the ground water.

As the outflow route was understood to be through the trenches between the turbine building and the sea, as a countermeasure to prevent outflow into the sea, Tepco dammed up the trenches between the mountain side and the sea side.

Thereafter, it was indicated that there is a possibility that the highly concentrated contaminated water accumulated in the trenches passed through earthquake-damaged parts and spread through the permeable gravel layer.

It had been understood since the accident that close to 20,000 tons of contaminated water was accumulated in the trenches, but no radical solution such as purification or removal was carried out.

Furthermore, it is feared that some of the large quantities of contaminated water accumulated in turbine building basements are leaking out through the trenches even now.

Tepco's response to the present problem is severely criticized.

It took them one month to admit that ground water is leaking into the sea.

Tepco admitted how bad that response was, by saying: "concerned by commercial damage caused by bad image [to local fisheries?], as a priority, we withheld the conclusions until we obtained the data that support a final conclusion, rather than having an attitude of actively disclosing the risks".

Tepco did not put into practice one of the lessons from the accident formulated as "implement multi-layered countermeasures based on the worse case scenario".

http://ajw.asahi.com/article/0311disaster/fukushima/AJ201308030046 (03 August 2013)

calculations show that if the water levels continue to rise at the current pace, contaminated water will flood the surface in about three weeks.

...

According to one calculation, about 100 tons of groundwater would have to be pumped up daily to prevent the water from leaking into the ocean. But the plant is running out of storage space for the contaminated water.

 

[tsutsuji]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20130809/index.html In order to lower the ground water level, Tepco started drawing water from small scale wells near the shore protection bank at 02:00 PM on 9 August 2013. By the middle of next week, Tepco plans to insert thirty 5-metre long pipes into the ground and together they will provide a 100 ton/day water removing capacity.

 

[zapperzero]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20130809/index.html In order to lower the ground water level, Tepco started drawing water from small scale wells near the shore protection bank at 02:00 PM on 9 August 2013. By the middle of next week, Tepco plans to insert thirty 5-metre long pipes into the ground and together they will provide a 100 ton/day water removing capacity.

Amateur hour all over again. These guys never heard of Archimedes probably. That... is not how you dry out a piece of land.

 

[Rive]

Amateur hour all over again. These guys never heard of Archimedes probably. That... is not how you dry out a piece of land.

It's a trap.

With too low groundwater level the outflow from the trench to the groundwater would increase.
With too high groundwater level the outflow of the groundwater to the sea would increase.

As it seems now with the given water level in the trench there is no good (fast) solution.

 

[etudiant]

Drying out the site is probably undesirable, because the nuclear fuel is surely safer under 20 feet of water than exposed to open air.
What is wanted is to halt the flow of water through the site, because that carries ongoing contamination to the sea. However, because the ground water flow is down from the hills and into the sea, it must not only be prevented from entering the site, but also the sea must be prevented from replacing the ground water outflow with a saline inflow.
So the real requirement is to dike off the plant completely, which will require major work, because the bedrock is 60 feet down, if memory serves. The proposal to freezes the ground uphill from the site to create a barrier to the water inflow seems a reasonable first step which however must be coordinated with the already ongoing seawall construction to avoid pooling contaminated water on the surface of the site.
Is anyone in charge at Fukushima who has the ability to communicate how the various measures taken fit into the long term plan? It would be so helpful.

 

[etudiant]

Drying out the site is probably undesirable, because the nuclear fuel is surely safer under 20 feet of water than exposed to open air.
What is wanted is to halt the flow of water through the site, because that carries ongoing contamination to the sea. However, because the ground water flow is down from the hills and into the sea, it must not only be prevented from entering the site, but also the sea must be prevented from replacing the ground water outflow with a saline inflow.
So the real requirement is to dike off the plant completely, which will require major work, because the bedrock is 60 feet down, if memory serves. The proposal to freezes the ground uphill from the site to create a barrier to the water inflow seems a reasonable first step which however must be coordinated with the already ongoing seawall construction to avoid pooling contaminated water on the surface of the site.
Is anyone in charge at Fukushima who has the ability to communicate how the various measures taken fit into the long term plan? It would be so helpful.

 

[nikkkom]

Drying out the site is probably undesirable, because the nuclear fuel is surely safer under 20 feet of water than exposed to open air.

IIRC in Fukushima there are no known instances of accident-produced nuclear fuel outside of containments, so no fuel can be exposed to *open* air by drying.

In Chernobyl predictions that solidified core melt would generate dust by alpha-spalling proved wrong. In fact it turned out that corium "lava" is durable, is was hard to fracture it for obtaining samples.

 

[nikkkom]

The water level of the turbine buildings is kept lower than the local groundwater level, which causes a massive inflow. This inflow prevents the groundwater contamination around the turbine building and increases the water amount stored in the site.

However, there are some 'forgotten' power cable trenches between the turbine buildings and the main seawater pumps. These trenches are filled with water from the turbine building. And the water level of these trenches - which is ~ the same as in the turbine building - is clearly higher than the groundwater level around the seawater pumps. This causes an outflow there.

How many centuries TEPCO needs to find and block those trenches? :(

 

[SteveElbows]

I have been waiting for news of the next attempt at looking in the pedestal area of reactor 2. The previous attempt as detailed on August 2nd took too long, so they had to end it prematurely. (as discussed in this document: http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2013/images/handouts_130802_06-e.pdf )

But as I have not seen any fresh documents, I am assuming the next attempt is running behind schedule? I can see from one of the Japanese daily updates that something that sounds like the water sampling that was supposed to happen the day before the next attempt may have taken place, but the computer translation of the paragraph in question is very poor. So I was wondering if someone would be kind enough to translate it properly?

2号機原子炉格納容器の滞留水採取作業を実施。採水終了後、装置(サンプリングホース・カメ ラ)をガイドパイプに収め、X-53 ペネの中に引き抜き、ペネからガイドパイプを引き抜くことができ なかった。8/8、装置(ガイドパイプ)の引き抜き作業を実施したところ、ガイドパイプについては回 収できたが、カメラとサンプリングホースの吸い込み口部分が無くなっていることを確認。8/12 以 降、作業の検討などを踏まえて、原子炉格納容器内部調査の未実施分を調査する予定。

It's from the 2nd page of this document: http://www.tepco.co.jp/nu/fukushima-np/handouts/2013/images/handouts_130809_03-j.pdf

Many thanks.

 

[Rive]

How many centuries TEPCO needs to find and block those trenches? :(

It'll be some weeks to get through the usual papermill of permissions and such: also some time the prepare the equipment they need and start.

What is a more relevant question here (IMHO): how could they forget those trenches? There was a really serious leak there at the beginning of '11.04.

 

[tsutsuji]

2号機原子炉格納容器の滞留水採取作業を実施。採水終了後、装置(サンプリングホース・カメ ラ)をガイドパイプに収め、X-53 ペネの中に引き抜き、ペネからガイドパイプを引き抜くことができ なかった。8/8、装置(ガイドパイプ)の引き抜き作業を実施したところ、ガイドパイプについては回 収できたが、カメラとサンプリングホースの吸い込み口部分が無くなっていることを確認。8/12 以 降、作業の検討などを踏まえて、原子炉格納容器内部調査の未実施分を調査する予定。

It's from the 2nd page of this document: http://www.tepco.co.jp/nu/fukushima-np/handouts/2013/images/handouts_130809_03-j.pdf

Many thanks.

[On 7 August 2013] Unit 2 PCV accumulated water sampling work was performed. After completing the water sampling, the equipment (sampling hose, camera) was put back into the guide pipe, and pulled into penetration X-53, but it was not possible to pull the guide pipe from the penetration. On 8 August, as we undertook the work of pulling the equipment (guide pipe), we could retrieve the guide pipe, but we found that the camera and the sampling hose's sucking mouth part were missing. From 12 August onwards, based on the study of the work, we plan to perform the still not executed part of the PCV internal survey.


Thanks, Steve, for keeping us informed of the unit 2 PCV investigations.

 

[tsutsuji]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20130810/index.html In wells located 2 m away on the mountain side, the ground water level was found to be about 60 cm above the solidified ground underground wall (16 m deep, but the shallowest part 1.8 m from the ground surface is hard to solidify, and water can overflow the wall in that part). This means that the solidified ground underground wall has lost its function.

 

[Rive]

This means that the solidified ground underground wall has lost its function.

Now they have a target level to reach with the water pumping.

 

[tsutsuji]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20130812/index.html There was an NRA working group meeting on 12 August. They announced a plan to remove 60 ton/day from the unit1 and unit 2 area in order to keep the water level below the underground wall. Together with the unit 3 and unit 4 area, they want to remove 80 ton/day from next month. The NRA instructed to reinforce water level monitoring during the typhoon season.

 

[LabratSR]

I have been waiting for news of the next attempt at looking in the pedestal area of reactor 2. The previous attempt as detailed on August 2nd took too long, so they had to end it prematurely. (as discussed in this document: http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2013/images/handouts_130802_06-e.pdf )

But as I have not seen any fresh documents, I am assuming the next attempt is running behind schedule? I can see from one of the Japanese daily updates that something that sounds like the water sampling that was supposed to happen the day before the next attempt may have taken place, but the computer translation of the paragraph in question is very poor. So I was wondering if someone would be kind enough to translate it properly?



It's from the 2nd page of this document: http://www.tepco.co.jp/nu/fukushima-np/handouts/2013/images/handouts_130809_03-j.pdf

Many thanks.

http://ex-skf.blogspot.com/2013/08/fukushima-i-nuke-plant-reactor-2.html

 

[Bandit127]

Ten workers at the crippled Fukushima nuclear power plant were exposed to radiation from contaminated mist, TEPCO says. Workers in the building were prohibited from using tap water, which comes from the same tainted source 10 km from the facility.

http://rt.com/news/fukushima-workers-contaminated-radiation-393/

 

[tsutsuji]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20130813/index.html When they left the plant premises at 00:40 PM on 12 August, 10 employees were found to be contaminated mainly on their face and head. The highest contamination was 19 Bq/cm², which is 5 times Tepco's internal standard. The cause is being investigated. The mist generators installed as a countermeasure against heat strokes in the surroundings of the earthquake-isolated building are suspected. The contaminated employees were working indoors, but they took the bus in front of the earthquake-isolated building which is used as a base. Also, an air radiation alarm rang in this area in front of the earthquake-isolated building.

http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2013/images/handouts_130812_03-e.pdf Alarm Went off at the Dust Monitor Installed in front of the Main Anti-earthquake Building

http://www.tokyo-np.co.jp/article/national/news/CK2013081302000129.html The contaminations are between 4 and 19 Bq/cm², which is 5 times Tepco's internal standard but less than the legal limit requiring decontamination. Tepco said [such contamination] "does not bear consequences on health". In order to investigate the cause, Tepco will check the mist generator's sprinklers, check each contaminated employee's movements, and examine the possibility that the bus could have projected contaminants upwards.

 

[SteveElbows]

Thanks very much for the translation tsutsuji.

Documents in english related to the subsequent reactor 2 investigation (after that water sampling one) are available in english now: http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2013/images/handouts_130812_06-e.pdf

As usual the image quality is rather poor and the ambient dose info obtained isn't released yet. I wonder when they hope to do the actual investigation of the pedestal area, using penetration X-6 instead of X-53.

 

[Rive]

As usual the image quality is rather poor ...

Once they release the video of the investigation I plan to look after that.

 

[LabratSR]

The video is posted.

http://photo.tepco.co.jp/en/date/2013/201308-e/130812-02e.html

 

[Rive]

Not much can be done with the images I'm afraid:
- they are using some kind of filter to remove the worst of the radiation 'hits': this filter is interfering with the averaging
- they did not show the most interesting places/did not checked the interesting places
- the light is still low

Anyway, at least the noise could be removed.

 

[Rive]

One more thing: I bet they are also using some variation of this trick, the video has many 'still' parts, ideal for averaging...

 

[tsutsuji]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20130815/index.html After the pumping from small scale wells that was started on 9 August, Tepco began on 15 August before midday the full scale ground water pumping using some of the planned thirty 5-metre deep pipes whose installation has been completed. After 18 August, when all pipes will be completed, the pumping capacity will reach 60 ton/day. Since pumping began, the ground water level has declined by about 50 cm. Even after the ground solidifying work will be completed, up to 35 ton/day of ground water is expected to seep out to the sea through the solidified layer, so that a radical solution is still wanting.

 

[LabratSR]

From Ex-SKF - Fukushima I Nuke Plant: Alpha Nuclides Found in Condensed Water from Reactor 3's PCV Gas Control System

http://ex-skf.blogspot.com/2013/08/fukushima-i-nuke-plant-alpha-nuclides.html