Japan Nuclear Watch, 3/29: Defense in Depth Now Has Sandbags!
It’s 10:00 pm EDT here; it’s 11:00 a.m. Tuesday in Japan.
Sandbags. That’s right, we’re literally down to sandbags to keep a trench filled with highly radiative water from spilling its content into the sea. From NHK World (and see video of drawings here):
On Monday, the power company detected radiation of more than 1,000 millisieverts per hour on the surface of puddles in the No. 2 reactor’s turbine building and in a trench outside the building.
The concrete trench stretches toward the coast but does not connect to the sea.
Puddles of water were also found in the trenches of the No.1 and No.3 reactors.
The No.1 reactor’s trench will overflow if the water rises by 10 centimeters. TEPCO has blocked the trench outlet with sandbags and concrete to prevent the water from reaching the ocean.
The water in the trenches of the No.2 and No.3 reactors is reportedly 1 meter from overflowing.
To provide context, recall from our last update that TEPCO was trying to figure out how to remove contaminated water from two to five feet deep in the lower rooms of each of the turbine buildings. There is a turbine/generator building next to the reactor building at each Unit of the Fukushima Daiichi Nuclear Station.
Apparently, the water is leaking from somewhere, still unknown, along the chain of pipes and valves coming from the reactor into the turbine building and eventually returning to the reactor. In the turbine building the pressurized steam enters and turns the turbine/generators. The expanded, now cooler steam then passes through a condenser where it becomes water. Then it’s further filtered for mineral buildup and then piped/pumped back into the reactor building and returned to the reactor.
So an initial plan was to pump the contaminated water into the condenser tanks, putting it back into the closed loop leading back to the reactor. But apparently the condensers for Units 2 and 3 are already full.
The authorities still don’t know where the water leaks are occurring along that chain. But given the levels and types of radiation, that water is presumable picking up radiation from the damaged fuel rods in the reactor, suggesting fuel rod disintegration and fuel deterioration inside (what the media are calling “melting”). Japanese officials have essentially admitted there is some degree of core damage or “melting” in Unit 2.
There may also be contaminated water in the large pressure suppression pool beneath the reactor core. They suspect this structured was damaged in the explosion more than a week ago in Unit 2.
[Update, Tuesday a.m. EDT: the “trenches” appear to be several meters deep and filled with water (h/t powwow). Recall that these lower levels nearer the ocean were flooded by the tsunami, so most of the water could be left over from that, with only part of it contributed by leaks from inside the turbine building. Since the first reports, I haven’t seen updates that indicate the levels are rising, and if so, how fast. So for the moment, its yet another large pool of contaminated water they have to monitor closely and work around.]
In addition to not knowing the source/location of the water leaks within the turbine building, they can only guess at the rate at which water is leaking. That means that as they continue to inject water into the reactor to keep the core from overheating, they have to guess at how much water/pressure they can “safely” inject without exacerbating the leaks that are flooding parts of the turbine building next door. And now, it seems the leaked water accumulating inside the turbine building is following gravity on its way to the ocean, via a tunnel that leads from the turbine building towards the sea.
And each of those tunnels is close to overflow, so they’re literally piling sandbags and concrete to erect a barrier to hold it in until they can figure out how and where to pump it out.
They can’t get close enough to find the leaks, but they have to keep injecting water. The more they inject, the more they have to worry about it overflowing and eventually spilling into the ocean. Inject too little, risk further “melting” in the reactor; inject too much, risk further ruptures and worse leaks and an overflow into the sea.
And in the meantime, there’s now a clear pathway for high radiation levels from the damaged reactor to the open environment.
In slightly better news, they’ve found traces of plutonium in soil samples near the plants that, they claim, are not much elevated from normal levels. Here’s a Q&A from Kyodo News on what this may mean. Detailed readings here (h/t Selise).
Nuclear Power Plant Primer — good expert video
Unit by Unit status updates (pdf) at the IAEA site