TEPCO is now reporting another leak in one of the pit tanks at Fukushima Daiichi. The number 3 pit tank has now been found to be leaking and strontium was found outside the tank. TEPCO claims only 3 liters of water has leaked from this tank but fails to explain how such a small amount of water vs. a huge tank could be determined.
The number 3 tank sits next to the number 2 tank TEPCO admitted was leaking large amounts of highly contaminated water on Friday. The water held in the number 3 tank is the same type as in the number 2 tank. Jiji is reporting that the radiation levels around the number 2 tank are rising. TEPCO claims they have set up an emergency task force to deal with their latest blunder. At this point there is no plan to transfer water out of the number 3 tank. There may not be anywhere else to move it to, TEPCO doesn’t say.
This may not be the end of the problems with water storage. It was reported back in February that an above ground tank was found to be leaking where the panels of the tank bolt together. Since these tanks are bolted together rather than welded this creates yet another problem since each tank has many panels and there are fields of these tanks. Will someone be running around with a wrench re-tightening bolts periodically? Fukushima Diary estimated the tank panel gaskets have a life of only 5 years but didn’t provide a clear source for this estimate. This is certainly possible and both the high radiation and salt in some of the contaminated water will accelerate any corrosion and break down in those tanks.
Back to the pit tanks, the construction of these is rather sub standard even for the original intent of holding the clean-ish tritium laced water from the ALPS system. We explored this issue of pit tanks back in 2011 as TEPCO was planning to purposely dump more water into the sea. When we looked at the issue it was intended as an emergency stop gap to prevent dumping the untreated water to the sea. This was before TEPCO began building the tank and treatment systems at the plant. Our report on the tactic of pit or bladder tanks suggested something of a higher safety margin than TEPCO chose to use. Even US sewage retention ponds require a higher standard than was used in TEPCO’s pit tanks. It does appear to be a situation of someone in the construction & design process deciding to go on the cheap.
Normally even a sewage pond is required to use something like a thick layer of bentonite clay to prevent leaks and leeching into the ground water. This vendor of clay products explains how that is done for sewage ponds. A thin sheet of bentonite clay fabric as was used in the tanks at Daiichi is clearly sub standard. TEPCO chose HDPE sheet for lining the tanks. Our research showed there were better options even if these tanks were only to hold post ALPS water.
This EPA report on low level radioactive waste ponds describes what is the expected minimum for such holding ponds in the US. The EPA examples show the use of a thick clay layer, multiple membranes, soil layers and a drainage system to divert anything that could potentially leak past. The contrast to TEPCO’s three layers of HDPE plastic and a 6.5mm bentonite fabric show how sub standard these ponds are even to hold the post ALPS water. Since TEPCO has been pushing for permission to dump the post ALPS water directly into the sea, their rationale could have been that this was “good enough” since they intended on releasing it to the environment anyways. What has not been told by TEPCO is who made the decision to dump the highly radioactive water into the ponds or why they chose to put this water into the ponds rather than transferring some of the less radioactive water into these ponds.
So far potential causes of the leaks have been that the seams in the plastic sheets are leaking. This is TEPCO’s guess. Other potential problems considered are that the soil beneath could be shifting due to fault lines and the constant earth quakes in the area. Sharp rocks, burrowing animals and the plastic framework used inside the tanks are all potential sources of puncture of the liners.
TEPCO’s handout on the new leak
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