Plutonium no worry (yet) at Fukushima, but beware the puddles

Today, the Tokyo Electric Power Co (TEPCO), which runs the Fukushima nuclear power plant, announced that environmental samples taken a week ago indicate the presence of plutonium in the soil near the plant. The levels remain low, and pose little threat to those working on getting the reactors back under control. More worrisome from that perspective is the finding that highly radioactive water has been found in tunnels away from the reactor building proper, suggesting that there have been leaks from elsewhere in the containment structures. Combined, these findings confirm previous indications that there are problems with the integrity of both the reactors’ fuel rods and its containment system.

Thanks- J. Trimmer

As far as human health risks, the plutonium isn’t a serious concern at the levels it was detected; according to a Reuters report, levels were similar to those found in Japan in the wake of nuclear testing done elsewhere, and unlikely to put workers at risk due either to toxicity or radioactivity. Its presence, however, does indicate damage to the reactor’s fuel rods has been sufficient to allow some fuel to escape with the steam vented from the plants.

The hydrogen explosions that occurred at the site were triggered by a high-temperature reaction between the fuel rod’s covering and steam, which had indicated this sort of damage was likely (we’ve described this previously). So, to a certain extent, the plutonium finding confirms what we’ve already expected.

The contaminated water may be a more significant problem, in that the levels of radiation it is emitting may be sufficient to cause radiation sickness after exposures of an hour or so, according to a BBC report. Given that many on the cleanup crews are already pushing exposure limits that have been raised in response to the crisis, this makes the cleanup even more challenging. A CNN article indicates that the equipment used to concentrate the radioactive isotopes in water is already backlogged with liquid from other sites at the reactor, so it may take a while to clean up these new sites of contamination.

Also worrisome about the new site of contamination is its location: a tunnel that’s connected to the plant’s turbine room, where steam from the reactor is used to generate power before being cooled and returned to the reactor core. This indicates that there are probably failures of containment outside the reactor proper; currently, it’s not clear where the water originated, how far it spread before being detected, or what isotope is involved (cesium and iodine isotopes have been the primary sources of contamination). This latter item will be key to understanding the long-term risks posed by this material.

The biggest worry with this water is that it may indicate an open cooling system. Fresh water is being injected into the cooling system in order to keep the reactors’ temperature down; it will invariably pick up radioactivity due to exposure to the damaged fuel rods in the core. If it simply leaks out of the system afterwards, then the cleanup crews may face an unappetizing choice: continue to pump in water that increases on-site contamination, or limit water use and risk having the reactors overheat again (or further). Finding and fixing the source of the leak may be impossible due to the high exposure risks the water creates.

The latest worries come despite considerable progress at the site, including the restoration of power and a changeover from salt to freshwater for the injections into the cooling system. They reinforce how fluid the situation is, and how little ability we have to detect and control some of the events occurring at the site.


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