Wigner energy

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Wigner energy (discovered by Eugene Paul Wigner ) is energy that can be stored in the crystal lattice of graphite . It plays a role in the safety of graphite- moderated nuclear reactors .

Physical background

During the operation of the reactor, the graphite is irradiated by fast neutrons . This allows carbon atoms to be shifted from the crystalline lattice structure to interstitial positions. The graphite expands slightly as a result and crystal defects occur that store energy. The graphite is partially metamict . This stored energy is called Wigner energy. It can be released spontaneously and suddenly as heat. Since such an uncontrolled rise in temperature represents a safety risk, the Wigner energy stored in the moderator must not become too great.

The imperfections begin to recombine from around 250 ° C and gradually release the Wigner energy. Therefore, the moderator can be " baked out ". To do this, the reactor must be kept at a correspondingly high temperature for some time. In the case of graphite-moderated high-temperature reactors , “bake-out” takes place automatically during operation, as the core temperature is sufficiently high.

Windscale accident

When trying to use the stored Wigner energy of the air-cooled graphite moderator of the Pile No. 1 in Windscale (better known today as Sellafield ), the Windscale fire broke out in 1957 .

See also