structure to realign itself before any potential energy could be stored. Wigner energy may have played some part following the prompt critical neutron spike, when the accident entered the graphite fire phase of events. Dissipation of Wigner energy A buildup of Wigner energy can be relieved by heating the material. This process is known as annealing. In graphite this occurs at . Intimate Frenkel pairs In 2003, it was postulated that Wigner energy can be stored by the formation of metastable defect structures in graphite. Notably, the large energy release observed at 200–250 °C has been described in terms of a metastable interstitial-vacancy pair. The interstitial atom becomes trapped on the lip of the vacancy, and there is a barrier for it to recombine to give perfect graphite. Citations General references Glasstone, Samuel, and Alexander Sesonske [1963] (1994). Nuclear Reactor Engineering. Boston: Springer. . . Condensed matter physics Crystallographic defects Nuclear technology Physical phenomena Radiation effects