How to deal with contaminated water


Question:

How could the contaminated water at the Fukushima Daiichi be treated to make it safe for the environment? (70s or above, Tokyo)

Answer:

TEPCO has found thousands of tons of highly contaminated water in the trenches and the underground floor of the turbine buildings of units 1, 2, and 3 at the Fukushima Daiichi nuclear power plant. Their efforts to transfer the water into the surface condensers have had some success, but the larger portion of the water has yet to be removed. The contaminated water also needs be made safe before placed into the environment.

There are two options available to treat radioactive water: either store it for a very long time to let radioactive substances decay, or filter the radioactive substances out of the water. The first option requires a large storage space, while the latter requires development of a water treatment system. At Fukushima Daiichi, the contaminated water needs to be isolated first. The question is, if radioactive substances in the water can be filtered out.

Let us consider the case of Three Mile Island. The nuclear accident also left thousands of tons of water contaminated with cesium-137 in the basement of the unit 2 reactor building. The Three Mile team used an absorbent material called zeolite to filter radioactive substances in the water. Zeolites are aluminosilicate minerals that have large pores inside the structure and are highly efficient ion exchangers and absorbers; therefore, they are also widely used in industry for laundry detergents and air fresheners. At Three Mile, zeolite successfully removed cesium-137 and most of other radioactive substances, though with some exceptions of hard-to-isolate substances such as tritium.

The water cleanup process at the Fukushima Daiichi will be a struggle against time. It took the Three Mile team months to develop the system that pumped the water out and filter it through zeolites. TEPCO is unsure if such time can be afforded. Radioactive water is still leaking from the damaged reactor. To make room for the highly contaminated water, TEPCO has dumped ten thousand tons of low-level radioactive water into the ocean, and now plans to build temporary storage tanks. TEPCO also just outlined a plan to develop a system that would purify water and reuse it as cooling water, which will take several months to build. Finding space for the water and treating it will be the central challenges at the Fukushima Daiichi in the months to come.


Science Communicator: Misato Hayashida


Links

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