FUKUSHIMA — While contaminated water continues to accumulate at the crippled Fukushima No. 1 Nuclear Power Plant, radioactive waste retrieved from that water during purification work is becoming a serious concern for the nuclear facility.
Since there is currently no way of dealing with the waste, plant operator Tokyo Electric Power Co. (TEPCO) has stored it onsite as a temporary measure. But there are fears in Fukushima Prefecture that it may be left there for good.
Contaminated water builds up every day at the Fukushima No. 1 plant as groundwater flows into the reactor buildings where melted fuel from the Fukushima nuclear disaster lies. Since this contaminated water could flow into the sea, TEPCO processes it with several types of purification equipment, and reuses it to cool the No. 1 to 3 reactors.
Tainted water in the reactor buildings is pumped into the U.S. cesium absorption apparatus Kurion and Toshiba Corp.’s Simplified Active Water Retrieve and Recovery System (SARRY) to remove radioactive cesium and other materials. The water is then desalinated and sent through the Advanced Liquid Processing System (ALPS), which can remove 62 different types of radioactive substances.
This process, however, does not eliminate the radioactive materials themselves; they are soaked up by absorbents, such as minerals. Radioactive materials build up in these absorbents, which remain as waste emitting high levels of radiation. This type of waste is stored in metal containers that isolate the radiation. As of Nov. 10, there were 178 such containers at the SARRY processing area, 758 at Kurio and 2,179 at ALPS. The size of the containers differs depending on the area, but overall, it amounts to some 11,000 cubic meters — which would fill around 30 25-meter swimming pools. These containers of waste stand in a temporary storage area on the south side of the plant’s No. 4 reactor.
Isao Yamagishi, a group leader at the Japan Atomic Energy Agency, warns, “Waste produced during water purification work is highly radioactive, and so is the risk of just keeping it in storage.” This is because even if the tainted water goes through a desalination process, salt can remain in the waste. There is a risk of the waste containers exploding if the concentration of hydrogen in them — produced due to the effects of radiation on water — reaches a certain level. Such a phenomenon was seen at the No. 1 and 3 reactor buildings of the Fukushima No. 1 plant, which exploded due to an accumulation of hydrogen soon after the outbreak of the disaster.
Yamagishi says that salt content has a tendency to aid hydrogen production, and it is necessary to release a sufficient amount of hydrogen from the containers. It is also possible that salt could corrode the metal containers. There do not seem to be any problems with hydrogen concentration or corrosion at this stage, but Yamagishi says, “We need to research over the long term what’s going on inside the containers.”
There is additional nuclear waste at the plant, too. Soon after the outbreak of the nuclear disaster, a decontamination system provided by France’s Areva SA was put into operation, and approximately 597 cubic meters of radioactive waste produced during the water purification process with this system remains stored at the plant.
The Nuclear Regulation Authority says that if the Fukushima plant is hit by another major tsunami, this waste could end up outside the plant. It therefore needs to be dealt with quickly, but there is nowhere for it to go.
Contaminated water also poses a problem. The ALPS system cannot remove radioactive tritium from the water, so tritium-tainted water is stored in tanks. There are about 1,000 tanks holding this type of water, whose total weight amounts to some 900,000 metric tons. And as work to decommission the plant’s reactors increases, both the amount of nuclear waste and the amount of contaminated water will increase.
Shigeaki Tsunoyama, former president of the University of Aizu in Fukushima and head of the Fukushima Prefectural Center for Environmental Creation, who is familiar with the field of nuclear safety engineering, comments, “Locals are concerned that nuclear waste will be left there as it is.”
In the future, work will begin to remove melted fuel at the Fukushima No. 1 plant, but its destination remains undecided. Some locals fear that if no destination for waste designated as being in “temporary storage” at the plant is decided, then Fukushima will become the final disposal site for melted fuel in the future. Tsunoyama is calling on officials to provide a map for the future.
“I want them to analyze the long-term risks, and provide an outlook for the storage and disposal of waste,” he says.
http://mainichi.jp/english/articles/20161126/p2a/00m/0na/004000c
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