March 16, 2011
Engineering Department
Fukushima: Waiting For the Magic Bullet
Here's something I'm wondering about. Maybe some of you can help me out, or point out where I'm going wrong...
The situation at the Fukushima Daiichi plant is just continuing to deteriorate, with damage at all three fueled reactors, containment cracks at two of them, and overheating spent fuel pools at one of the shutdown reactors, with more spent fuel problems likely.
The heat in the reactors comes from decaying fission products. The initial rate of decay is very fast, giving off a lot of heat. That fast decay uses up a lot of fission products, which means the rate of decay, and therefore heat output, drops pretty quickly. But as the decay rate drops, so does the rate at which the fission products are used up, meaning that reduction in decay heat slows down.
According to the MIT Department of Nuclear Science and Engineering's estimates of decay heat, after the reactors were shut down, the decay rate dropped by half in the first minute, then by half again in the next half hour, then by half again about 16 hours later, and so on. Today, the reactors are probably each putting out between 6 and 12 million watts of power (depending on which reactor), but that amount isn't going to go down much more in the near future. By the end of the month, they'll still be putting out between 5 and 9 million watts. It will take a year for the heat output to drop to half of what it is now.
In other words, the battle at the power plants isn't going to come to an end by itself. However, there is one thing that can stop the overheating, stop the leaks, and return the spent fuel pools to normal. It's a magic bullet, or like Superman coming to the rescue, except it's totally real.
The magic bullet that will solve nearly all the problems at the Fukushima Daiichi plant is kind of ironic: The power plant needs power. Since the earthquake hit, the plant has been off the Japanese power grid, and since the tsunami an hour later, all of the backup diesel generators at the plant have been inoperable. Thus, none of the cooling systems at the power plant have been working.
As soon as the plant site gets power, the reactor wouldn't have to be cooled using fire engines for pumping. Operators could just start the Emergency Core Cooling System (or whatever the call it in Japan), which would drain hot water from the pressure vessel, cool it in a heat exchanger, and pump the cool water back over the reactor cores. Everything will cool off. The water will stop evaporating to steam, the vapor pressure will go down, and radioactive material will no longer be released because the pressure vessel and containment won't be venting the pressurized steam.
They wouldn't need elaborate and dangerous plans to re-fill the spent fuel pools using helicopters. They'd just turn on the pumps.
People have got to be working on this. They've got to be trying to reconnect the plant to the national power grid. They've got to be trying to repair the diesel generators at the plant site. They've got to be trying to bring in new generators.
Yet I haven't been able to find news coverage of the effort to resupply the plant with power. Does anybody out there have more information about this? Or am I misunderstanding the situation?
Update: While I was writing this, CBC Canada answered it:
A new power line could soon restore electricity to cooling systems at Japan's tsunami-damaged nuclear plant, its operator said early Thursday, a development that would reduce the threat of a meltdown.
Construction of the line is nearly complete, said Tokyo Electric Power Co. spokesman Naoki Tsunoda, and officials hoped to try it "as soon as possible." The potential for a meltdown at the Fukushima Daiichi complex remains, however.
(Hat tip: repstock1, confirmed by MIT NSE)
Update: On the other hand, MIT MNE folks say it may not be as easy as running a power line:
The problem with the spent fuel pools is not a want of generators, but a want of electrical connection. Flooding of electrical switch gear has left the generators unable to be put into service.
So I guess they're going to have to repair and replace some of the switch gear as well.
Update: Just to be clear, given that the reactors have been through earthquakes and a tsunami and explosions and fires and contamination and salt water, the problems aren't going to go away instantly--calling it a magic bullet was a bit of hyperbole--but things will get a hell of a lot easier once they can get the pumps running. Everything going on right now is a holding action until that happens.
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MY IDEA IS GET ONE OR TWO HELICOPTERS CARRYING A LONG HOSE AND LOWER THE HOSE WITH THE FRONT PART LONGER AND WEIGHTED INTO THE OPENING AND DROPPING IT AS NEEDED TO BE ABLE TO HOOK UP CONNECTING HOSES AND TURN ON A WATER OR COOLING SOURCE.I HAVE A SKETCH IF NEEDED.