Wigner Energy and the Sellafield Fire

 

I have posted before about Wigner's contribution to Quantum Mechanics so I was excited to see he was featured in the exhibition about Sellafield in The Beacon at Whitehaven. Turns out that the Wigner Effect is that a neutron going into a moderator like graphite knocks a whole atom out of its position in the lattice if the neutron has sufficient energy. This can knock out other atoms etc. Some of these atoms don't make it back into the lattice but stop in the gaps between the lattice atoms, in the interstitials. The lattice is the place with least energy so these interstitial atoms have more energy. If there are enough of them and they all release their extra energy at once, that will raise the temperature enough to be dangerous. See here for my source and more details.