APR: your source for nuclear news and analysis since April 16, 2010

Monday, March 28, 2011

Contaminated water in trenches outside turbine buildings.. update

Now that we've gotten some more solid data, let's talk about what's known and what it might imply (if anything) and what can be done.

Each turbine building has, outside of it, underground and heading toward the ocean, a tunnel. The tunnels contain pipes and wires.. the pipes are for cooling the condenser and the diesel generators. This tunnel is a separately poured concrete structure from the turbine building; in other words it is its own area, with its own walls. The wall between the turbine building is not a common wall; there are separate walls for each structure. Rubber seals and other types have been used to seal pipe penetrations.

The trench doesn't run all the way to the ocean.

Now, access to these "trenches" which really are tunnels is through two fairly large manholes; one right near the turbine building and one further down toward the shore. These manholes actually cover shafts that run as much as 60 feet or so down to where the trench or tunnel actually is.

All three plants have water in these manhole shafts nearly all the way to the top. In other words, not only is the trench or tunnel full but the access shafts are nearly filled up, up to ground level.

ONLY IN NO.2 PLANT IS THE WATER HIGHLY CONTAMINATED IN THE TRENCH. This water measured over 1000 mSv/hr just like the water in the turbine building. The water in the other two plants' trenches is not anywhere near this, and seems not to be a problem right now.

But the contamination level in No. 2 plant's trench is a concern. Probably the best thing to do in the very short term would be to rig up a submersible pump that could be lowered into the manhole, fitted to a pipe with a filter or two in line. The water could then be pumped into a tank truck, or a couple of tank trucks, and moved away to another location on site, still in the trucks, to wait for further filtration and disposal or else left to sit for decay. If the water were out, further buildup could be prevented and access of this water to sea would be made much more difficult.

NISA isn't exactly sure how the water got into the trenches given the sealing applied to the pipes. However it's pretty certain, at least in my eyes, that the piping seals are sure to be found the culprits since they're meant to seal off the areas but not hold continuously for a week or so against deep pools of water in the plants. Or, perhaps condenser or seawater pipes are ruptured; or the tsunami flooded them somewhat through the manholes if they weren't sealed properly. Or there may be cracks in the turbine buildings and the trench walls. No one will know until they can get down there, and that won't happen until the water is all out.

The major inter-industry flap will be because the trench, outside the turbine building, is not considered as a "controlled area" whereas the turbine building (and of course the reactor building) is a controlled area. Every effort is always made every day in normal ops to prevent contamination in any uncontrolled area. Sure, you don't want it anywhere at all but the presence of any contamination in an uncontrolled area is considered serious.

HOWEVER, given that there are destroyed reactor buildings, release of radioactive contamination into the air and ocean already, I'd have to say that this is a minor problem at this particular moment. I would hope that the tank truck method would be used to quickly get this water into a controlled condition.

5:50 AM Eastern Monday 3/28
ATOMIC POWER REVIEW

3 comments:

  1. A very large tanker barge is due for arrival about now.

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  2. The news reports I read stated that the tunnel for unit 3 was inaccessible due to debris from the explosion and could not be checked. The workers that received radiation burns to their feet were working in unit 3's turbine room if I recall.

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  3. There is water in No. 3 trench, nearly to the top, as reported by NISA officials during a briefing and repeated by TEPCO update. TEPCO says debris is preventing them from measuring activity at the surface. In other words they can see the water through a grating or holes but can't remove the lid yet.

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