Keiji Takeuchi
Keiji Takeuchi is the Senior Staff Writer of the vernacular Asahi Shimbun. He has covered nuclear-related issues, such as the Chernobyl nuclear power plant accident in 1986.
Veteran journalist Keiji Takeuchi
A mass mobilization structure was forming Friday at the Fukushima No. 1 nuclear power plant for what could prove the decisive battle in preventing a further deterioration of the situation. Defeat could possibly lead to a huge release of radioactive materials into the air.
The Self-Defense Forces and Tokyo’s Metropolitan Police Department have joined the efforts, with the immediate focus on spent fuel rods in storage pools at the nuclear plant.
While not at the radioactive level of fuel rods in the reactor core, spent fuel rods have what is called decay heat. The temperature of the water in the storage pools in the No. 3 and No. 4 reactors has been rising because the water circulating systems malfunctioned, reducing the water level in the pool.
If a large amount of water can be supplied either by spraying or with a restoration of electric power, the spent fuel rods would be cooled and the situation could become more stable.
Spent fuel rods are highly radioactive waste that releases extremely strong radiation. If even small parts of the rods are exposed, the surrounding area could become too dangerous for the workers.
If water cannot be pumped in, the water level will fall and the fuel rods could melt under their own heat. While it is difficult to predict what will happen after that, the worst case would be if the melted fuel rods accumulated at the bottom of the pool.
The fuel rods contain uranium and plutonium, raising concerns the materials could reach a critical stage in which continuous nuclear fission occurs. However, the elements in the control rods that would also melt could restrain the reaching of the critical stage.
While the attention has been on efforts to spray water into the reactors, the pressure containers surrounding the cores of the No. 1 to No. 3 reactors are still in an emergency situation.
Although the internal situation is unclear, the fuel rods were likely exposed for a long time, meaning a partial core meltdown has probably occurred. That possibility calls for the immediate pumping in of water. A fire hose was used to try to pump in water, but the high pressure within the container kept the water out.
If a strong power source is restored, the emergency core cooling system (ECCS)–considered a guardian deity for preventing major nuclear accidents–would finally operate. That would make possible a high-pressure pumping of water and would likely once again submerge the fuel rods. But there are questions about whether the ECCS can still operate.
The Great East Japan Earthquake and subsequent tsunami have destroyed equipment at the nuclear plant that had been considered sturdy. If water cannot be successfully pumped into the core, the fuel rods will gradually melt. The temperature at which that melting occurs is 2,800 degrees. The rods would turn to mush and slowly drop to the bottom of the pressure container.
Most of the steel equipment around the container will begin to melt when temperatures reach 1,500 degrees. This is what actually happened at the Three Mile Island nuclear power plant in the United States in 1979.
About 70 percent of the fuel rods melted, and a clump of melted fuel reached the bottom of the container. But it stopped there, one step away from a major disaster. Workers must prevent the cores of the No. 1 to No. 3 reactors at the Fukushima plant from moving toward what happened at Three Mile Island.
In the worst-case scenario, the melted fuel rods would drop to the bottom of the container and open up a hole. Although the melted mass could stop there, if it reached the nearby suppression pool and came in contact with water in the pool, a steam explosion could occur.
The containment vessel surrounding the pressure container would likely be unable to withstand the shock and pressure from such an explosion. If that happened, a large amount of radioactive materials would be released into the atmosphere.
The biggest issue facing the Fukushima No. 1 nuclear power plant is that five emergencies are occurring simultaneously while the circumstances at each are unclear. The five situations are in three of the reactors and two storage pools containing spent fuel rods.
If a worsening of this serious situation can be stopped now, a massive release of radioactive materials can be avoided. With one week having passed since the earthquake, the central government has deepened its sense of crisis, and various efforts to spray water are being undertaken.
Until now, there was a tendency to leave matters in the hands of Tokyo Electric Power Co., which operates the nuclear power plant. There finally appears to be signs that the abilities of all of society are being brought together. That effort must be intensified.
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This article was first published by the Asahi Shimbun.
