Blog Archive

Friday, 5 June 2015

Recovery, remediation, decommissioning at Fukushima

Managing contaminated water involves removal of the sources of contamination and isolating ground water from sources

Full remediation and decommissioning of reactors at Fukushima may take a long time. Hasty schedules are not possible or expected as they clash with the safety of people. Water flowing over the melted cores of Units 1, 2 & 3 stricken by the earthquake and tsunami carries a cocktail of radio-nuclides. The integrity of the primary containment vessels of these reactors is not known. They have to develop the needed technologies to handle the cores; it may face its own trials and tribulations.
Fukushima now witnesses a beehive of activity. In April 2013, exactly two years after the accident, the site engaged 2950 workers in various remediation tasks. By February 2014, the work force grew steadily to 7150.
Mr. Naohiro MASUDA, chief decommissioning officer and president of Fukushima Daiichi Decontamination and Decommissioning Engineering Company presented updates of the progress thus far, and the future plans at an international conference organized by the Japanese Atomic Industrial Forum on April 13-14, 2015 at Tokyo.
He covered, among other topics: the present status of the plants; measures against contaminated water; fuel removal from the spent fuel pool and fuel debris removal.
The Tokyo Electric Power Company (TEPCO) maintains the reactors at cold shutdown stage by continuously injecting water into them. The operators removed spent fuel rods from the spent fuel pool at Unit 4 by Dec 22, 2014. Now they plan to remove fuel debris from Units 1, 2 and 3.
Maximum dose rate at the site boundary is only 0.03 mSv per year, as against allowed limit of one mSv per year.
Managing contaminated water is a humongous challenge. It involves removal of the sources of contamination, isolating ground water from sources and prevention of water leakage.
TEPCO uses 16 specially designed pieces of equipment each of which can remove one or more of the sixty-two different radio-nuclides including caesium-137 and strontium-90 from water. Each may process 250 to 1200 cubic metres per day. Tritium is a major issue. TEPCO is reportedly discussing with fishermen for its gradual release into sea.
Daily, about 400 tonnes of ground water enter the building. As this water gets contaminated, it has to be stored and decontaminated. Besides other methods, TEPCO plans to construct a frozen soil impermeable wall on the land side to prevent entry of ground water. The wall will use refrigerated coolant at minus 30 degree Celsius, running through pipes that have been placed vertically in the ground, to freeze the surrounding soil.
“There are many underground pipes and other structures associated with each of the four generating units. Building a watertight physical structure around all those obstacles would be nearly impossible and, even if it could be done, the construction would be more complex, time consuming, and disruptive.
It likely would also generate much more potentially contaminated excavated soil that would need to be safely disposed of,” TEPCO stated at its website...
The wall will be in place for six years, the period needed to drain and clean the contaminated water from the buildings and make them watertight.
According to Hiroshi Kainuma, Fukushima University, the yield of rice in Fukushima came down from 4, 45, 700T in 2010 to 3, 53,600 T in 2011. In 2013, it rose to 3, 82,600T closer to earlier years.
In 2012, 71 bags of food had radioactivity above the legal reference value. In 2013, 28; in 2014, no such bag was found.
Neither abortions nor abortion rates have increased in Fukushima. Divorce rate has not increased.
Birth rates lowered. Kainuma noted that the number of direct deaths caused by earthquake and tsunami in Fukushima was 1612; the number of disaster-related deaths due to evacuation was higher at 1793!
Decontamination specialists, with unenviable tasks assigned to them used, on large industrial scales, technologies which were successfully deployed on small scales. There were failures. Diligent auditors did not condone such ‘aberrations.’ You may express empathy or sympathy or hostility on that action depending on which side of the isle you are in!
The reactor owners, regulators and others responsible to operate the Fukushima Daiichi plants safely managed to melt the cores of three of them, throwing nuclear industry world-wide into disarray! Ultimately, the Japanese ingenuity and their expertise in robotics, miniature electronics, and precision engineering will win the day. Japan needs nuclear power; many plants will start operation, though presently only energy specialists look at them benignly.
Source : The Hindu
Post a Comment