August 17, 2013
The build-up of stored wastewater at Fukushima Daiichi is a serious problem, at least as far as the Japanese press is concerned. Currently, there is almost 360,000 tons of Cesium-stripped water being stored in above-ground tanks. The rate of build-up is about 400 tons per day. Eventually, at some point in the future Tepco will run out of room for more tanks and fill them all. I would like to suggest a way to possibly stop the build-up of stored waters, and not diminish the rate of decontamination in the process. Why not set up a closed loop through the Cesium-stripping system?
Let me explain. Currently, about 770 tons per day is pumped out of the highly-contaminated waters in the basements of units #1 through #4, and run through the Cesium absorption system. About 370 tons of the Cesium-stripped water is sent into the three damaged reactor cores to keep them cooled, and subsequently finds its way back into the basement volume through as-yet-unidentified pathways from the Reactor Pressure Vessels. The remaining 400 tons is pumped into available above-ground tanks. The basement water levels ought to be dropping at a rate of about 400 tons per day. But to the contrary, the water levels remain constant. It means that groundwater is somehow leaking into the basements, keeping the water levels from changing. Why not put the 400 tons per day of Cesium-stripped water back into the basements from where it originated? By sending the cleansed waters back into the basements, Tepco would be utilizing what is known (in the vernacular) as a “closed loop”.
It is likely the top of the water in the basements is parallel to the top of the groundwater in the earth outside the basements. There are several reasons why this is likely. For one thing, Tepco did not discover the groundwater in-leakage until they lowered the basement waters down to the now-existent levels, and could not get them to reduce further. Not only does this indicate at point of internal/external equilibrium had been reached, but it also suggests that the in-leakage is significant and would accelerate if Tepco increased the rate of flow to the Cesium absorbers. Next, water naturally “seeks its own level”. Finally, groundwater level in the earth remains relatively constant over time and levels in the basements have been relatively constant since late 2011. It thus seems that sending the same volume of cleansed waters back to the basements as the volume now being supplied by groundwater in-leakage should keep the system in equilibrium. In other words, sending the cleansed waters back to their source will not cause the water levels in the basements to increase above where they have been for more than 18 months.
A closed loop would provide several positive benefits. First, the build-up of tank-stored water at Fukushima Daiichi would effectively cease, possibly ending concerns of Tepco running out of space in the future. This has been a concern of nuclear critics and antinuclear politicians for more than a year. Ridding themselves of this constant news story would do Tepco’s public information staff a world of good. Next, once the new decontamination system for the ~60 remaining isotopes (ALPS) is in full operation, there will be more than enough tanks to hold the Tritiated effluvia until the ocean discharge issue is resolved. After a currently-filled tank is emptied, it could be flushed of any residuals that remain and re-filled with water that has had all radioactive isotopes removed, other than Tritium, by ALPS.
In addition, a closed loop would continue diluting of the Cesium concentration in the basement waters at about the same rate as with the groundwater in-leakage. The Cesium absorption system is actually working better than initially expected. Tepco estimated (in 2011) that the system would lower the Cesium content by a factor of up to 1,000. It’s actually lowering Cesium content by about a factor of 10,000 (from 55,000 Becquerels per milliliter down to 5.5 Bq/ml). That’s 10-times better than its design. Not bad for a “makeshift” technology, eh? In fact, if the groundwater outside the basement walls is as Cesium-contaminated as a few recently-discovered-to-be-contaminated test wells indicate, the Cesium-stripped water would be lower in concentration than the groundwater now entering through the basement walls! If this is the case, then the Cesium-cleansed waters from the “makeshift” system will actually reduce the Cesium content in the basements faster than the current groundwater in-leakage.
This not-so-immodest proposal puts Tepco into a Pascalean dilemma. Should they recycle the cleansed waters back to the turbine building basements or should they not? They have nothing to lose and everything to gain by switching to a Cesium-stripping closed loop. However, they have nothing to gain and (inevitably) everything to lose by maintaining the status quo. It seems to me that the answer is a virtual slam-dunk.