In the the daily Fukushima Nuclear nightmare recap, the juxtaposition of two of the bullet points really jumped out at me from the present situation with the damaged reactors at Fukushima.
• TEPCO continues to inject nitrogen into No 1 reactor to prevent another hydrogen explosion
• Officials estimate it will take months to stabilize the nuclear reactors and years to clean up toxic fallout
Sounds reassuring, doesn't it. I had also seen elsewhere that nitrogen was being used to reduce the threat of another hydrogen explosion. Sounds like they have a plan. They found a way to avoid more hydrogen explosions, and it seems to be working. It will take time and effort, but eventually everything will be stabilized and cleaned up. Well, I feel much better now.
Well, actually, I don't feel better, because I know that Nuclear Reactor No. 1, like its brothers and sisters all over the world, was designed and built and operated with many tons of the most highly purified zirconium. When a nuclear reactor starts producing hydrogen, it is only because zirconium in the reactor has overheated and is breaking down.
Check the details of how this works here and here. The short version is this.
Zirconium is a useful metal for nuclear reactors because it doesn't interfere with the flow of neutrons among the fuel rods, but it is unstable. In ordinary air, finely powdered Zirconium can spontaneously combust and the higher the temperature of zirconium,the less stable it becomes. At excessive temperatures, contact with air and water will cause spontaneous combustion of reactor zirconium in which oxygen is taken up and hydrogen is given off. A properly operating or shut down reactor gives off no hydrogen of any significance. There is hydrogen only when the reactor becomes too hot and the zirconium fuel rods begin to burn and breakdown.
Given those facts, these ideas occurred to me:
Operators are only introducing nitrogen to Reactor No. 1 to fight an ongoing build-up of hydrogen; otherwise, they wouldn't bother. Of course, they could just be reacting prophylacticly and out of caution and fear that the operators don't really know what the reactor is doing inside the containment.
Nuclear reactors only produce hydrogen when coolant control is lost and zirconium fuel rods overheat and begin to break down, burn and melt.
Fuel rods in nuclear reactors do not begin to break down, burn and melt unless the operators of the reactor have lost control over reactor cooling.
Nuclear reactor operators do not allow the reactor to operate at such high temperatures if they can find any way to avoid it.
A pronouncement that the situation will not be stabilized for months, to come, at Fukushima is also an admission that the situation is not stable now.
So, TEPCO and the Japanese government admit that they can't be sure they have control of Reactor No. 1, which they fear may be producing hydrogen. How reassuring is that? Keep your eyes glued to Reactor No. 1 etc.