tsutsuji said:
Contaminated water treatment countermeasure Committee (2nd meeting), 16 May 2013
3-1 contaminated water quantity reduction response measures
http://www.meti.go.jp/earthquake/nuclear/pdf/130516/130516_01k.pdf (2)
Translation :
Contaminated water quantity reduction countermeasures
1) Waterproofing of penetrations
Suppress by barring the openings or gaps of penetrations of underground trenches or pipes connected to buildings
Problems/feasibility:
Prediction of seepage routes and quantities;
Selection of waterproofing target locations;
Implement worker exposure reduction measures in locations with high radiation (high air dose rates, presence of high concentration contaminated water etc.).
2) Practical use of ground water bypass
Wells are dug on the western side of building which is the ground water flow's upsteam side, and by the forced bypass of the ground water flow to the buildings, the ground water in building vicinity is controlled.
Problems/feasibility:
Accurate control of ground water level in order to prevent in-building accumulated water leakage;
Suitable water quality control.
3) Practical use of subdrain
Ground water level around buildings is lowered by pumping up water from wells in buildings' vicinity.
Problems/feasibility:
Restoring and installing new subdrains in high radiation areas or where the work interferes with other works;
Running the subdrain in ajustment to the pumping out of the accumulated water, under accurate control of ground water level in order to prevent in-building accumulated water leakage;
4) Waterproofing of the gap between buildings
Buildings are set leaving an about 50 mm gap before the neighbouring building's underground wall. Because the penetrating pipes between buildings are concentrated, we waterproof the gap thus suppress ground water seepage.
Problems/feasibility:
Implementing worker exposure reduction measures in high radiation dose areas;
Performing the work where obstacles, such as underground structural parts, are present;
Interference with other works such as fuel removal.
5) Mountain side water insulating wall
By the installation of a water insulating wall such as a slurry wall or a frozen soil wall on the mountain side of the buildings (either on the OP 10 m or on the OP 35 m layer), the ground water flow from the mountain side to the buildings is suppressed and the ground water level in building vicinity is lowered.
By the control of the in-building accumulated water water level in adjustment to the lowered ground water water level, the seepage into buildings is refrained.
Problems/feasibility:
If a mountain side water insulating wall is built, controlling the amount of ground water level reduction in building vicinity is difficult. Especially during the duration of the work, it is feared that the ground water level around building becomes lower than the in-building accumulated water water level, and there is a risk that accumulated water seeps out.
6) Reactor building accumulated water water level control
After waterproofing between reactor building and turbine building (or radioactive waste building), the difference between reactor building accumulated water level and ground water level is reduced so that ground water seepage diminishes. Being located on the mountain side, the surrounding ground water level is higher around the reactor building than around the turbine building. By actively controlling the reactor building's water level and reducing the water level difference, the seepage of ground water is refrained.
The items needed to implement this response are:
- Installation of reactor building water exhaust equipment
- Waterproofing between reactor building and turbine building (or radioactive waste building)
Please note that inter-building waterproofing, while being relevant to reduce contaminated water boundary, is presently being planned as a way to dry up, as part of neighbouring buildings are being removed in order to install the foundation etc. in the case where a containment covering the reactor building is built for the purpose of fuel debris removal etc..
Problems/feasibility:
Reactor building water level control
It is necessary to secure technology to control the reactor building accumulated water level while monitoring the difference with the ground water level.
7) Filling torus room with grout
Penetrations, etc. are waterproofed by injecting grout into torus room (reactor building basement), so that ground water seepage into reactor building is reduced.
The items needed to implement this response are:
- Installation of equipment to take accumulated water from PCV.
Problems/feasibility:
It is necessary to secure waterproofing technology that is effective in stopping seeping water from downstream.
8) Filling building (turbine building) basement with concrete
By filling turbine building basement with concrete, ground water seepage into turbine building is reduced.
Problems/feasibility:
Removal of existing equipments;
Removal of existing equipments such as basement pipes, ducts, etc.
Treatment of accumulated water;
Building basement accumulated water pumping out and treatment.
Radiation reduction;
Reduction of air radiation so that work, such as existing equipment removal, is possible.
9) Polymer enclosure of turbine building basement contaminated water
By enclosing turbine building basement contaminated water with polymer, ground water seepage into turbine building is reduced.
Even if ground water seeps in, it can be converted into water devoid of tritium.
Problems/feasibility:
Remaining existing equipments;
It is impossible to completely absorb the water contained inside existing basement equipments such as pipes, ducts, etc.
It is necessary to check whether absorbed water may come out due to aging, etc..
Securing polymer treatment technology;
It is necessary to secure treatment and disposal after waterproofing
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.
11) Practical use of treated water into concrete
When tritiated water is used as concrete mixing water, 180 litre of water can be used per 1 m³ of concrete.
Under the hypothesis where 700,000 tons of tritiated water are used as concrete mixing water, 3,900,000 m³ of concrete have to be made.
If concrete making unit cost is estimated between ¥ 10,000 and ¥ 15,000 per m³, the concrete making spending amounts to about between ¥ 39,000,000,000 and ¥ 58,500,000,000.
Also, if we use crushed contaminated debris as concrete aggregate, it contributes to the global reduction of the total amount of waste. If we use the flyash from Hirono thermal power plant, it can contribute to the reduction of thermal power waste.
Application examples:
Application 1: for the construction of a 60 m wide base, 30 m high gravity type sea-wall covering the area in front of units 1 to 6, about 1,800,000 m³ are needed.
Application 2: If the harbour is filled with concrete, from 1,000,000 to 3,000,000 m³ are needed.
Application 3: If the valleys inside the plant premises are filled with concrete, the usable plant premise area is expanded. From 1,000,000 to 2,000,000 m³.
Application 4: Making concrete blocks, they can be assembled into a 230 m base, 146 m high pyramid, requiring 2,600,000 m³.
Problems/feasibility:
Environmental impact evaluation;
- Evaluation of consequences of tritium eduction after concrete coagulation
- Evaluation of consequences of mixing water vaporisation generated during concrete solidification
Increase of radioactive waste
It is possible that it becomes radioactive waste.
12) Exchange of deep layer ground water and tritiated water (proposal by committee member Maeda)
Exchange tritiated water with deep layer water so that it remains underground for the time until radiation sufficiently decreases by radioactive decay.
Problems/feasibility:
Study to be continued.
13) Manyfold barrier system construction (proposal by committee member Marui)
Construct a manyfold barrier (water insulating wall ?)
Problems/feasibility:
Study to be continued.
14) Building bottom soil freeze (proposal by committee member Maeda)
In addition to frozen soil barrier, the building's bottom is also turned into frozen soil.
Problems/feasibility:
Study to be continued.
15) water insulating wall, water pumping wells, facing, horizontal well combination (proposal by committee member Nishikaki)
(a) Perform assessment to obtain ground layer information
(b) Perform assessment to evaluate the continuity of the layer thought to be a low permeable layer. Check if that layer has about 1.0 E-6 cm/s permeability and 5 m thickness.
(c) If the low-permeable layer can sufficiently prevent the rise of ground water from downstream, the construction of a water-insulating wall near the boundary line can cut the ground water flow from upstream into the contaminated area.
(d) The ground water from above the water-insulating wall should permeate downstream making a detour around the water-insulating wall, but if it flows into the contaminated area by overflowing over the water-insulating wall, wells are dug in those locations in order to prevent upstream water level from rising.
(e) Even if the ground water percolation from upstream is cut, as cutting percolation and flow from rainfalls onto the surface is difficult, a urethane type waterproof layer or asphalt layer is installed in order to reduce percolated flow.
(f) Against ground water leaking upwards from the aquifer below the low-permeable layer, horizontal wells are installed into the lower aquifer in order to reduce ground water pressure.
(g) When the upper aquifer water level drops, there is a possibility that reactor building or turbine building accumulated water flows out, but this is addressed by the installation of a layer that waterproofs the ground around buildings.
Problems/feasibility:
Study to be continued.
