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» Tritium is a serious obstacle to work to decommisionning

Getting the radioactive element tritium out of even treated water has become a serious obstacle to work to decommission the plant’s reactors.

Tritium is also known as “hydrogen-3″ as it has one proton and two neutrons in its nucleus, while hydrogen has only a single proton. Its half-life, the time it takes to decay and become half as radioactive, is 12.3 years. The beta rays it emits travel only around five millimeters in air, and only around 0.005 millimeters in water or in the human body.

The International Atomic Energy Agency (IAEA) released a report at the end of last year on its evaluation of decommissioning work at the Fukushima plant that read, “Tritium is practically not accumulated by marine biota and shows a very limited dose factor” and therefore “has a very limited contribution to radiation exposure to individuals.” It suggested release of tritium to the ocean be considered.

One reason for releasing tritium into the ocean is the difficulty in separating and removing tritium from water.

Another reason is the cost of treating tritium. The advanced thermal reactor Fugen, now decommissioned, used to have equipment that could process 30 kiloliters of tritium-contaminated wastewater a day. However, the cost was around 20 million yen per metric ton of water, meaning it would cost more than 10 trillion yen to process all some 520,000 tons of contaminated water at the Fukushima plant.

Meanwhile, contaminated water continues to build up at the Fukushima plant, as every day around 400 tons of underground water flows into each of the nuclear reactor buildings, which still hold their melted nuclear fuel. Tokyo Electric Power Co. (TEPCO) processes the water to remove cesium and sodium and stores it in on-site tanks, of which there were around 1,080 as of mid-February. The water is planned to be processed by the Advanced Liquid Processing System (ALPS), which is currently being run experimentally and is expected to remove 62 varieties of nuclear material, such as strontium, from the contaminated water.

However, due to ALPS’s technical limitations, tritium will remain in the water even after treatment. As of the end of 2013, the contaminated water at the plant was estimated to contain 875 terabecquerels of tritium. The Fukushima plant is only allowed to release 22 terabecquerels’ worth of tritium into the ocean per year, meaning the contaminated water amounts to what would normally be released over the course of around 40 years. TEPCO is considering releasing the water into the ocean anyway, but faces stiff local opposition.

 

<Media Report>
Radioactive tritium stands in way of Fukushima reactor decommissioning (Mainichi Newspaper)


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