I was recently at a Nuclear Safety meeting where heat flows out of piles of solid were being discussed. Some of you will be aware of the fact that one of the things which I am involved with is the chemistry of serious nuclear accidents. As a result I do have dealings with a range of nuclear safety experts, I am aware that to some people get over heated or angry at even the phrase “nuclear safety”. Some of these people are saying that this phrase is an oxymoron; I would like to know why they hold this view.
Sadly our roads are often the scene of vile carnage and death, I suspect that sadly many of my readers have like me seen a serious road crash or the immediate aftermath. But we still feel happy about the existence of “road safety” professionals who work in both the private and public sector. For example we have vehicle inspectors, seat belt experts, experts who try to make car wrecks less fatal and the person who came up with the “green cross code”.
Many of these road safety experts spend a lot of their time looking at how road accidents occur and trying to work out how to prevent or mitigate them. In the same way nuclear safety experts tend to spend a lot of time thinking about the causes, mechanisms and the best responses to nuclear reactor malfunctions. So if it is OK to call a road wreck expert a “road safety” professional then a nuclear accident expert can be a “nuclear safety” professional.
One of the things I saw at the meeting was the question of how the heat will flow out of a pile of resolidified nuclear fuel which would be generated when the fuel in a reactor melts and then pours out of the bottom of the reactor pressure vessel.
The cooling of a pile of wreckage in a pool of water under a reactor is a complex matter. The porosity of the pile has a great influence on the ability of water to cool the pile of wreckage and stop it heating up again and causing more trouble. One thing which I was thinking of was a more simple problem of a flat slab of resolidified fuel which is emitting decay heat which is sitting on the floor of a containment.
I was thinking of the worst case of a slab of fuel (a pancake of fuel) which is solid and not porous, as a result it is impossible for the water to circulate inside it and thus cool it. After talking to some physics experts I have worked out how I will consider the maths of the problem.
I intend to try to work out the right equations for this problem this weekend, when they are ready I will put them on the blog.