- Posted by Anthony Harrington, April 26, 2011
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Japan’s Tepco (Tokyo Electric Power Company) seems to be on a winning path, finally, in its long struggle to get on top of the nuclear meltdown at its damaged Fukushima nuclear plants. The 45-meter-high tsunami which struck the plant on March 11 (it was 7.5m at the shore, but peaked at the moment of impact with the nuclear reactor) rocked the global nuclear industry to its foundations and put question marks over reactor builds across the world. This being the case, the fact that Tepco looks as if it can finally see some light at the end of what has been a very long and dark tunnel will be widely welcomed. What the nuclear industry will not relish, however, is the fact that the genie is out the bottle as far as the public’s fear of radioactive materials is concerned.
Even the “mop up” phase of Tepco’s clean-up is replete with scary statistics. The company has to pump some 168 tonnes of fresh water per day into the reactor core of Fukushima Daiichi 2 to keep the rods from going into further meltdown. But some of that water is escaping from the reactor core and is accumulating in the turbine basement building. Initially, the “run-off” was making its way back to the sea through a 20 centimeter crack in a works shaft from the reactor that is close to the sea, generating readings in local sea water that were thousands of times higher than the prescribed safety levels.
Since Tepco plugged that crack, the highly contaminated water in the basement has been rising steadily. The company now estimates that there is some 25,000 tonnes of water in the basement and the levels are rising all the time. The initial flooding of the basement seems to have come from the reactor coolant circuit and the intense radiation levels in the water suggest that at one point some of it was in direct contact with partially melted fuel rods.
According to World Nuclear News, the surface of the water in the basement is emitting radiation at the rate of over 1000 millisieverts per hour. There are 1000 millisieverts (a measure of radiation absorption by the human body) in a gray, and a dose of one gray is enough to provoke serious radiation sickness and possible death. A three-gray dose will kill half of all adults inside a month. Any worker trying to deal with the water in the basement would pick up a one-gray dose within an hour. Yet water levels cannot be allowed to continue to rise or the sheer weight of the water would threaten the stability of the structure. The water is also way too radioactive to simply be vented to sea, as Tepco did with 11,500 tonnes of much more lightly radioactive water earlier in the proceedings.
The company’s solution, which is where the light at the end of this terrifying tunnel comes in, is to pump the contaminated water out of the basement and into a centralized waste treatment building at the plant. Pumping will proceed at 480 tonnes a day, which should empty the basement of its existing content in six days. Once in the waste treatment building, the contaminated water will be chemically “scrubbed” to remove the contaminants and the cleaned-up result will provide coolant water for the second reactor in a closed loop system. This solution will simultaneously resolve the build-up of water, find a use for the existing contaminated water resource and do away with the ad-hoc cooling arrangements that generated the water build-up in the first place.
This still leaves the problem of what exactly the damage is in reactor two that allowed the flow into the basement in the first place. Tepco was able to use remote-controlled robots to assess conditions inside the reactor buildings of units 1, 2, and 3 at Fukushima Daiichi on April 17/18, according to World Nuclear News. The robots were PackBot ground robots from the US-based iRobot. Measurements taken by the robots showed that at worst radiation levels were around or in excess of 50 millisieverts per hour in both reactors 1 and 3, with data on 2 still to be released. The company is also using an unmanned helicopter to photograph and film the damage to the outside and upper sections of the reactor buildings, damaged earlier by hydrogen explosions at the plant. While there are still serious hurdles to overcome, there is some optimism now that Tepco has at last begun to get a grip on the whole, nightmarish scenario. Nevertheless, it is all too much for the Italians, who this week voted to extend indefinitely their moratorium on nuclear new builds as far as its recently relaunched nuclear programme is concerned. It is unlikely to be the last country so to do.
Further reading on nuclear power and power generation
- Fusion power will change everything for business, by Anthony Harrington [blog post]
- Why the World Needs a Green New Deal, by Achim Steiner and Pavan Sukhdev
- Shining a Light on Global Solar Growth, by Morningstar
Tags: Fukushima , Italy , Japan , Japanese earthquake , nuclear power , tsunami