The Japanese government has announced that the first step in the schedule for stabilizing the Fukushima Daiichi Nuclear Power Station has almost completed.The recirculating water injection system that purifies contaminated water used in core cooling and recirculates it as cooling water has also gone operational.
Compared to the shocking series of events in March, including explosions, release of radioactive materials and evacuation, the situations surrounding the power station have been relatively calm since.This has diverted public interest away from core melt and directed it to the cesium contamination of beef and soil.
Let me make something clear concerning cesium contamination.As detailed on the website of the Japan Nuclear Technology Institute, the spread and strength of contamination in this case are far smaller in scale than those reported following the Chernobyl accident, due to the existence of containment vessels and the absence of a graphite fire.
These factors are hardly discussed in Japan, but have attracted attention in Europe and the United States, establishing a calm acknowledgement of the safety of the nuclear power station despite having been exposed to such a devastating disaster.
The information originated from the U.K., and was received as a blessing in the United States where alerts in its fight against terrorism still remain.
As for the state of the core melt, no major change is anticipated in the future, judging from the conditions over the past few months.Yet, it is impossible to achieve the state of cold shutdown (solidification of molten core) in 3 to 6 months, as indicated in the schedule.
This is because of the nature of decay heat, as I have already explained.After four months from the accident, heat currently released is coming from radioactive materials with a long half-life.The thousand kilowatts of heat generated will not decrease so much even after 6 months after the accident.
The size of the molten core must be about 4 meters in diameter.Imagine a thousand kilowatts of heat contained in a space the size of an 8-tatami mats room.If it is a traditional Japanese room, it will burn down in no time.The current cooling system simply pours water on the core.Step 2 is nothing more than introducing recirculated water, with no stepped-up cooling action for solidifying the molten core.
However, the use of the recirculating system has the advantage of reducing contaminated water.
Heat of one thousand kilowatt per hour vaporizes 1.5 tons of water.
The cooling of three affected plants should reduce approx. 4 tons of contaminated water per hour.Based on this calculation, 100,000 tons of contaminated water currently on the site should all vaporize in 3 years.
As for the state of molten core itself, however, nothing has changed except for decay heat, which is reducing according to the laws of physics.In plain terms, nothing has been done to really bring the situation under control.The general sense of relief that seems to hang over our society today is an illusion created by the Japanese value of "harmony" and the desire to settle matters in ambiguity.
There have been two cases in which the molten core was solidified.One is the case of the Three Mile Island accident in the U.S., and the other is the case at Chernobyl in the former Soviet Union.In the TMI case, powerful pumps were activated to forcibly cool down the core to achieve solidification.At Chernobyl, the molten core flowed into basement corridors increasing its surface area, enhancing cooling by air, which led to solidifying the core.
To stabilize Fukushima, forcible cooling, like at TMI, is not entirely impossible but the opportunity seems to have been lost due to the significant contamination of water from the 4 months of water injection into the plants, and lack of necessary information such as the location and shape of the molten cores to be targeted with coolant.
The other option is air-cooling.This involves suspending the current cooling operation to let the core melt further and drop on the bottom of the containment vessel so as to increase the surface area before resuming cooling.Implementing this option requires the examination of several technical challenges, including the prevention of steam explosion.It is possible to safely implement this approach, but the implementation requires courage and meticulous care.
The third and final option is the "status quo" approach of leaving the molten core in running water and waiting for it to eventually solidify.This requires a substantial amount of time before solidification is achieved. For a country that prides itself on its technological advancement, inaction would be shameful.However, judging from the way things are going, this might be the chosen option.Whichever option it may be, the final selection will largely affect the future passage of our nation's efforts to stabilize the power station.
| 
