The job of rebuilding the neighborhoods and towns demolished by the Japanese earthquake and tsunami has begun but one area of cleanup will continue to be a problem for a long, long time. TEPCO’s Fukushima Nuclear Power Plant has been a nightmare since the earthquake and tsunami knocked the units off line. New information obtained with the installation of air purifiers that have allowed workers to reenter Unit One.
Things moved fairly quickly: by four hours after the tsunami hit, the levels of cooling water had dropped enough that the top of the fuel stack was exposed to the air. Shortly after that happened, the temperature in the core reached nearly 3,000°C, and the cooling water boiled off the bottom of the fuel stack. Melting of fuel rods started at 4.8 hours after the earthquake hit, and a partial meltdown had already occurred by 5.1 hours. According to TEPCO, any residual integrity in the fuel rods was gone by 15 hours after the quake, and the reactor core was emptied of fuel by 16 hours.
In other words the fuel in the reactor completely melted down within the reactor. Previous reports assumed that there had been only a partial meltdown. It was feared that a full meltdown would lead to further nuclear reactions that would destroy the containment vessel and release more radiation into the atmosphere.
According to Nature’s Geoff Brumfiel, the meltdown did breach the containment chamber and may have released fuel pellets into the concrete basement of the reactor. However, the rapid move to pour water into the building along with boron to neutralize any reaction, prevented the disaster from getting worse.
Unfortunately, all of the water poured into the reactor is now contaminated and no one is sure where all that water is. That poses a problem since the prevailing assumption is that where ever it has gone, it can’t be good.
The melted fuel poses another problem. How will that fuel be removed. Since it has breached it’s containment vessel, it won’t simply be a matter of removing the vessel. The crane inside of the reactor was damaged in one of the explosions so it won’t be any help. Added to that the fact that the fuel isn’t contained in one area and is not easily lifted out, and you have further issues with cleanup. Plus water still needs to be circulated to keep the fuel cool and prevent any further radiation leakage. The water circulation system is still not working nor will it be easy to fix it or build a new one.
Analysis of Units Two and Three still needs to be done. First however, they have to install the air purifiers in those two units as they did in Unit One. The fear is that they will find a similar result in those two units that will hamper cleanup efforts.
TEPCO has started building a containment vessel over Unit One to contain the mess inside and prevent further radiation leaks. That is only a temporary solution. Further such containment vessels may be built over Units Two and Three but that won’t be confirmed until further analysis can be done.
Oh, yes, and analysis on Unit One is not finished. There may be further revelations about the reactor meltdown. At the very least, it will be interesting to find out where all of the contaminated water has seeped off to.
Illustration from TEPCO