Last week’s problem at Fukushima was yet another leak of contaminated water. 

Last week’s problem at Fukushima was yet another leak of contaminated water. Will Davis explains it clearly.

Toyoshi Fuketa, a commissioner on Japan’s new Nuclear Regulation Authority (NRA), visited the plant to investigate the leak and said that Tepco, the operator of the plant, had not planned for possible leaks. He suggested that international help might be desirable.

It was the lack of planning by Tepco that contributed to the Fukushima power station’s disastrous response to the tsunami caused by an earthquake in March 2011. Before that, Japan’s nuclear industry had experienced other accidents, frequently associated with poor planning and characterized by evasion and lack of transparency in keeping the authorities informed. In 1999, hand-mixing enriched uranium in steel buckets, against safety regulations, at the Tokaimura reprocessing plant led to a criticality incident that killed two workers. In 1997, there was a fire and explosion at the plant. In 1978, control rods at one Fukushima reactor dislodged but the accident was not reported because utilities were not required to notify the government of such accidents.

The March 2011 accidents also showed that Japan’s nuclear regulation fell far short of what was needed for safe operation. The NRA was formed after a government investigation into what was needed. As a new agency, the NRA is feeling its way while dealing with the problems that remain at Fukushima. Tepco promised better performance after the investigation but is not delivering.

Tepco needs “to stop going from crisis to crisis and have a systematic approach to water management,” Dale Klein, the chairman of an advisory panel to Tepco and a former head of the U.S. Nuclear Regulatory Commission, said.

The problem of leaks has to do with the flow of groundwater through the site. Groundwater, like a river, flows to the sea, as in the illustration (from BBC, who attribute it to Reuters). The water picks up leaking water from surface tanks and flows through the lower parts of the reactor buildings and picking up radioactive isotopes, mainly cesium-137 and -134, but also some strontium-90. It then passes into the sea. The orange bar represents a “chemical wall” that has been emplaced, and a steel wall is under construction.

The problem is that the groundwater keeps coming from higher ground. So Tepco must pump water into the surface tanks to keep it from flowing over or around the chemical and steel walls. The longer-term solution is to keep groundwater from flowing through the plant area. Tepco has proposed to freeze soil upstream of the plant to divert the water and prevent it from becoming contaminated.

At the Sillamäe site in Estonia, groundwater was carrying contaminants into the Gulf of Finland as it flowed under an enormous tailings pond a kilometer long. The solution was to dig a deep trench around the pond to divert groundwater. The trench is between the weedy area in the foreground of this photo (my photo, 2011) and the grassed cover of the pond in the background. The two-lane road on the right provides scale.

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A trench might be possible for Fukushima, but the frozen soil wall can be put in place more quickly.

I did some quick calculations of what the radioactivity of the water leaking from Fukushima might mean for the sea, and it’s not much. The leak reported last week is of somewhat more radioactive water, but it’s a smaller amount. So it too is not much. The IAEA has recommended filtering the water to remove some of the radioactive isotopes and dumping it at sea. That would work too, if fisherman can be convinced it’s safe.

 

Cheryl

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