Fukushima Radiation Levels High, But Leak Plugged 322
jmcvetta wrote in with a story about Fukushima radiation levels so high that monitoring devices have been rendered useless. Levels outside the buildings exceed 100 millisieverts in some places. But the good news is that the leak is patched using 1500 liters of sodium silicate.
This is all meaningless (Score:4, Interesting)
Even if they get the hydrogen under control, the amount of water, the damage to the secondary containment, the likely damage to primary containment, the contamination of the site, it's not just that Fukushima Daiichi will never operate again. Daiichi will be entombed and left to decay for at least a decade, probably longer, much longer. All six reactors are lost, 5&6 are just not going to be operated because it is too hot to work there 8 hours a day.
While they wait for decay to lower levels enough for machines to clean things up, there will be continuing groundwater and soil contamination. They will have to build a new seawall and interceptor wells to limit (not prevent) contamination of the local sea. The local population won't be allowed within 12km, and they won't WANT to be within 20km or more. Agriculture will likely be ruined, having to wait for years to once again export their products. It's the Cesium isotopes that will cause the worst problems, and cause the lasting effects, and they are not able to contain this yet. Hopefully #3 won't blow a Plutonium cloud that, even if it were minimal, would poison the area for the forseeable future. There is no assurance that this will not happen.
This is already inevitable, and there will be no real discussion, because TEPCO cannot admit to the inevitable outcome yet. To do so is to admit defeat, lose all face, and watch them become a single-yen stock.
And somehow Japan needs to replace the generating capacity. Quickly.
Overall this situation is redefining 'worst-case'. It may have been simpler to have a couple of core melts and just pour concrete and sand over the whole damned thing. Now we've gotten broken containment, multiple vectors, and inadequate resources. Oh, and the Japanese way of self-reliance to the point of failure. Works for the residents and their migration, doesn't work for engineering problems.
The bad news (Score:5, Interesting)
Workers are pumping nitrogen into one of the reactors at Japan's damaged nuclear plant in an attempt to prevent an explosion caused by dangerously overheated fuel rods.
Officials at TEPCO, which operates the Fukushima plant, said a dangerous hydrogen buildup is taking place at its number-one reactor. Japan's NHK television quoted officials saying hydrogen is accumulating inside the reactor's containment vessel - an indication that the reactor's core has been damaged.
Crisis at Japan Nuclear Plant Shifts to New Blast Risk [voanews.com]
Chemistry 201: Why Is Fukushima So Gassy? [nytimes.com]
But there are reasons...that Fukushima is particularly vulnerable.
One is its recent use of seawater to cool the reactors's fuel rods and cores. In addition to the oxygen in water molecules, cold seawater can hold a great deal of dissolved oxygen gas. But warm water cannot; so as the seawater was heated in the reactor, the dissolved oxygen emerged and gathered in the empty space above the water.
(Ordinary reactor cooling water has had the oxygen removed from it by plant operators to reduce the possibility of rust.)
In addition, gamma radiation from the nuclear fuel in the reactor would continuously produce small amounts of hydrogen and oxygen by breaking up water molecules --- and the normal method of recombining these elements into water at such plants in a controlled fashion is no longer available.
Plants of the Fukushima variety usually have catalytic converters that accomplish that at the point where steam has run through the turbine and is condensed back into water for another trip through the reactor. But that path has been closed since the plant lost power at the moment of the March 11 earthquake.
Hydrogen can also emerge from the zirconium metal used as fuel cladding. One of the lessons of the Three Mile Island accident in 1979 near Harrisburg, Pa., is that when the cladding comes into contact with steam rather than water, it goes through a reaction that is akin to rusting; it picks up oxygen from the water molecule and gives off hydrogen.
This only happens at high temperatures, but uncertainty reigns at the moment about temperatures in the Fukushima reactor cores. With some cooling channels blocked, they are likely to have hot spots.
By design, boiling water reactors like these have far more zirconium metal in them than pressurized water reactors do. They boil water directly in the core, covering the fuel assemblies with a water/steam mixture rather than keeping them immersed in water. The water has to be directed to each individual fuel assembly and therefore each sits in its own zirconium box.
All of that zirconium is available for an oxidation reaction with steam in which the metal absorbs oxygen from water and turns to a powdery rust, releasing hydrogen.