Thursday, May 30, 2013

#Fukushima I Nuke Plant: Freeze Soil to Block Groundwater


I can honestly say "I knew that", because that's what one of our long-time readers, netudiant, suggested some time ago.

From Yomiuri Shinbun (5/30/2013):

凍土の遮水壁で汚染水抑制…政府委が設置方針

Control contaminated water by impervious wall of frozen soil, the government committee is to request

東京電力福島第一原子力発電所で増え続ける汚染水の抜本的な抑制策として、政府の汚染水処理対策委員会(委員長・大西有三京都大名誉教授)は、建屋周辺の土壌を凍らせて地下水の流入を防ぐ「凍土の遮水壁」の設置を打ち出す方針を固めた。

As a drastic countermeasure against the contaminated water that continues to accumulate at Fukushima I Nuclear Power Plant, the government committee on contaminated water treatment countermeasures (chairman Yuzo Onishi, professor emeritus at Kyoto University) has decided to propose the installation of the "shield wall of frozen soil", whereby the soil around the reactor buildings will be frozen in order to stop the groundwater from leaking into the buildings.

30日の会合で最終判断し、東電に実施を求める。

The final decision will be made in the meeting on May 30, and the government will tell TEPCO to implement the plan.

同原発の建屋には、地下水が1日平均400トンずつ流れ込み、汚染水増加の最大の要因となっている。

400 tonnes of groundwater per day are leaking into the reactor buildings, and it is the biggest contributor to increasing contaminated water.

凍土の遮水壁は、大手ゼネコンが提案した。地中に管を並べて打ち込み、管内に氷点下数十度の冷却材を循環させ、周辺の土壌を一定の深さまで凍らせる。これが、建屋内と外側との水の動きを遮断する壁となる。地下に構造物があっても大きな障害とならず、1~2年程度で設置できる。

The impervious wall of frozen soil was proposed by a large general contractor. Rows of pipes will be driven into the ground, and coolant at dozens of degrees below zero Celsius will be circulated in the pipes to freeze the soil around the pipes to a certain depth. That will become the shield that will block the movement of groundwater. Even the underground structures won't be much of an impediment, and the wall could be set up in 1 to 2 years.

コンクリート製の遮水壁を造るのと違い、凍土法は管をすべて埋設した後、一気に土壌を凍らせ、短期間で壁が完成する。このため、施工中に壁の内側で地下水が減るなどして、建屋内から放射性物質を含む汚染水が外へ漏れ出る危険は少ない。

Unlike the impervious wall made of concrete, the wall of frozen soil will be built in a short period of time by burying all the pipes and freeze the soil all at once. Therefore, there will be little danger that the contaminated water leaks out from the reactor building, as could be the case if the level of groundwater inside the wall gets lower during the construction of the concrete wall.


That large general contractor is Kajima, who has also created the unmanned debris removal system for the Reactor 3 operating floor. Kajima is famous for huge civil engineering projects like tunnels, and this method of freezing the soil is very well known to them. The other major general contractors, Taisei and Shimizu also submitted their proposals, which involved concrete walls like TEPCO has been contemplating and included a study of overseas examples of such impervious walls.

Let's see what TEPCO says, because, as "Happy", unnamed former worker and journalist Ryuichi Kino said in the AP interview, cost-saving comes first for TEPCO. This frozen soil method looks faster and cheaper than the concrete wall or underground bypass.

From TEPCO's 4/26/2013 document on "How to prevent groundwater from coming into the reactor buildings" pages 36-47 , Kajima's excellent presentation (compared to the other two):

Plane view. Surround the reactor buildings and turbine buildings of Reactors 1-4 with frozen soil wall of about 1,400 meters in circumference.


Sectional view.


How to create frozen soil wall.


How continuous wall is possible with frozen soil wall.


According to Kajima (from the presentation),

  • As long as the frozen soil remain frozen, the coefficient of permeability is zero (100% block of groundwater from flowing in).

  • Even if power is lost, the wall remain frozen for several months up to a year.

  • The wall self-repairs.

  • Small footprint for installation equipment (2x2 meters, as opposed to 15x15 for normal wall construction), easy to remove.

  • There is very little contaminated soil resulting from the construction of the wall.

  • Construction of frozen soil wall won't interrupt decommission work

  • By regularly replacing the coolant and pipes, the wall can be used for a very long time.


  • Remote monitoring of temperature is possible.


  • Continuous wall is possible.


Almost too good to be true!

12 comments:

Hélios said...

Hi Ultraman,

Fukushima Daiichi nuclear plant will become an earthly iceberg ?

I don't understand how 400 tons a day of groundwater will stay frozen in this area over time.

Anonymous said...

Sounds great, reality is always more difficult. But freezing the ground is a common method when you build subways. It is energy costly.

Thus the proper solution would have been to freeze the ground early on (since relatively quick to implement).

Anyway, for the long run freezing is not the best solution. So they should freeze the ground and then make a permanent wall.....

Anonymous said...

Freezing the soil was considered (and discarded) at Chernobyl too -- albeit the idea there was to freeze the soil *beneath* the molten core.

The necessity of building a wall in the ground around the reactor was pointed out by Gundersen shortly after the disaster, I think. Tepco is getting there now.

Beppe

sickputer said...

A barrier on 4 sides does not address the earthquake and corium holes underneath the buildings and the fissures in the mudstone. They are in a effect proposing a box with four sides and no bottom and expect it to stop water and radiation. Lots of luck with that plan.

At least the Russians dug underneath Unit 4 at Chernobyl...

Anonymous said...

How do they plan to get enough juice to keep the walls frozen, all through four seasons and many decades?

Build Fukushima Dai-San (No. 3) nuclear power plant? They haven't heard anything like 'global warming', have they?



Anonymous said...

I think Kyoto University's Koide was earlier in suggesting the wall. Either way, they were talking about conventional concrete walls, and they are no civil engineers.

arevamirpal::laprimavera said...

Helios, the plan is to stop groundwater from seeping into the reactor buildings and turbine buildings by freezing the soil in the wall shape. I believe groundwater will be pumped up into wells that exist already and those they are digging. Pre-accident, groundwater was controlled using the subdrain pits around the buildings but they were all contaminated by the accident.

Beppe, it's not that TEPCO has come around to that idea. They have been talking about conventional concrete walls, for both at the harbor and on the ground. But they will be made to adopt this plan instead by the government, it looks. TEPCO's president met the government minister who apparently told him to do so.

Anonymous said...

Primavera-san,
the main point I was trying to make is that the need for underground walls was known from day one and Tepco has not done anything yet. Maybe they really need to be told what to do by someone else but in this case why are they still getting their paychecks?

Beppe

Anonymous said...

One more thing... according to Wikipedia it is Kajima that built Fukushima so maybe the government is just subcontracting to the "usual" folks. Smells a little of same old nuclear business, as Fukushima did not exist.
On the other hand what can one expect: allow the LDP back into power and, guess what, another stock bubble. Same old over again, until bankruptcy.

Beppe

Anonymous said...

Beppe, as we say in the States: the more things change, the more they stay the same.
*mscharisma*

arevamirpal::laprimavera said...

Beppe, unfortunately nobody else have expertise other than these major construction companies who have built tunnels, bridges, nuclear power plants.

Anonymous said...

mscharisma,
yeah, sounds familiar... an equivalent literary quote is "everything has to change in order for nothing to change" (Tutto deve cambiare perche' nulla cambi), from "Il Gattopardo" by Tomasi di Lampedusa. However the LDP is not even that sophisticated: nothing changes, period.

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