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Can Fukushima’s Spent Fuel Pools Catch Fire?
Can Fukushima’s Spent Fuel Pools Catch Fire?
In this Fairewinds’ feature, Fairewinds Associates Chief Engineer Arnie Gundersen analyzes a US government national laboratory simulation video that shows nuclear spent fuel rods do catch fire when exposed to air.
This simulation video proves Fairewinds’ assertions that nuclear fuel rods can catch fire when exposed to air, and Arnie discusses the ramifications of this phenomena if the Fukushima Daiichi Unit 4 spent fuel pool were to lose cooling water.
The Sandia National Laboratories video in its entirety can be seen here.
Transcript:
Arnie Gundersen: Hi, I’m Arnie Gundersen from Fairewinds and today I would like to talk to you about fuel pool fires: are they possible, what causes them and what are the consequences. Related to that is why is everybody focused on Fukushima-Daiichi Unit 4. Before I get into the details, I need to go back and touch on a couple of basics. Inside a nuclear reactor, uranium splits and when it splits, it gives off 95% of the heat. That is what makes nuclear fission so neat is that one atom can give off an incredible amount of heat. The problem is that 5% of the heat remains in these pieces called fission products. That heat gradually decays away over 5 years, but for at least 5 years, these pieces, these fission products, have to be cooled. That part of the reaction does not occur in the nuclear reactor, it occurs in the spent fuel pool. Remember now, that the uranium is in a pellet, about the size of my pinkie, and these pellets are put into about 12 foot long rods. The rods are made of a material called zircaloy and that is the problem. Zircaloy can burn in air if it gets hot enough. And it is called pyrophoric, so when it starts to burn, water cannot put out the combustion.
Now these pellets and rods are put into bundles. The bundles are about that big and 12 feet high. And those bundles are then lifted out of the nuclear reactor and put into the spent fuel pool. Now we know zircaloy can burn. Back in April of 2011, Fairewinds put a video up where we showed a single zircaloy rod burning in air. And on that video, you can actually see the piece of zircaloy bouncing across the table top. And it was combusting on it’s own, there was no flame, and it was basically burning in air with no internal source of heat.
The question is, can that happen in a nuclear fuel pool? And what is it about Fukushima-Daiichi Unit 4 that has everyone concerned? There are 4 reactors in jeopardy at Fukushima-Daiichi. But everyone’s attention now has been focused on the fuel pool at Fukushima-Daiichi Unit 4. Why is that? Well, in the Mark I design, there is no containment over the fuel pool. And that means that if there is a problem in the fuel pool, there is nothing to trap the radiation and prevent it from going airborne. At Fukushima-Daiichi, Unit 4 though, an entire nuclear fuel core had just recently been removed from the containment, from the nuclear reactor, and was put into the spent fuel pool. That is what makes Daiichi Unit 4 unique. It has got an entire nuclear core, out of the reactor, out of the containment, and in the fuel pool. Related to that though, is the fact that Fukushima-Daiichi 4 is also damaged. There is a bulge in the bottom of it and I believe it is something called a first mode Euler strut bulge. And it clearly is an indication of a seismic damage. This is not something that happened from the explosion. The building has been damaged from a seismic event. So Daiichi Unit 4 has an entire nuclear core out of the containment in a spent fuel pool and the building it is housed in, has been previously damaged by the explosions in the building and by the seismic events that occurred since March 11th of 2011. That is why all eyes in the world are focussed on what is going on in Fukushima Daiichi Unit 4.
