Wigner Effect in Metallic Lattices

In summary, the Wigner effect is a term used to describe the damages in moderator material typically graphite. It is only found in giant crystal lattices and is not the suitable mechanism for metal lattices.
  • #1
nickandre
2
0
Hi,
I'm a bit confused with the Wigner effect concept. This effect is normally associated to damages in moderator material typically graphite.
But metallic cladding of the fuel element is also exposed to fast neutron, but Wigner effect is seldom being used as a term to explain the damages in the metallic lattice.
is Wigner effect only for giant crystal lattices, hence is not the suitable mechanism in metal lattice?
Hope someone can enlighten me on this

Thanks,

Confused
 
Engineering news on Phys.org
  • #2
The atomic bonds in carbon in graphite are very different that metallic bonds in metal. Neutron radiation causes damage in both types of materials in the form of dislocations (with vacancies and interstial atoms).

When the carbon bonds in graphite reform in the proper lattice (hexagonal lattice), they release chemical energy. To reform the graphite, it must be heated (annealed) to about 250°C.

Energy stored in the irradiated graphite of a graphite reactor. The graphite atoms located at the interstitials cause this energy storage ( See 'Wigner effect'). At graphite temperatures of more than 250° C these voids recombine releasing energy, the Wigner energy.
http://www.euronuclear.org/info/encyclopedia/w/wigner-energy.htm

In metals, the radiation damage is also in the form of dislocations, but there are no chemical bonds in the sense of graphite. In order for the dislocations to 'disappear', i.e. for displaced atoms to move back into the correct lattice positions, the metal must be heated above normal operating temperature, which is ~300°C in BWRs and 340-350°C in PWRs. The annealing temperature is about 500°C for Zircaloys for long annealing times. Zr-2 is usually annealed above 560°C, and Zr-4 above 600°C.

An interstial atom may be displaced some number of atoms from it's original location, therefore an interstial atom next to or near a vacancy is not necessarily the atom which orginated at that vacancy location.
 
  • #3
nickandre said:
Hi,
I'm a bit confused with the Wigner effect concept. This effect is normally associated to damages in moderator material typically graphite.
But metallic cladding of the fuel element is also exposed to fast neutron, but Wigner effect is seldom being used as a term to explain the damages in the metallic lattice.
is Wigner effect only for giant crystal lattices, hence is not the suitable mechanism in metal lattice?
Hope someone can enlighten me on this
nickandre,

Just to add to what Astronuc has already stated; metals also experience damage due
to neutron irradiation.

Fast neutrons can also cause dislocations in metals; which is why neutron-irradiated
metals become embrittled. Those dislocations decrease the ductility of the metal.
A metal can be annealed by heating it to high temperature and then cooling which gives
the atoms a chance to reconstitute the original crystal structure. However, in normal
operation of a reactor, temperatures that high won't be reached.

Graphite, however, anneals at a lower temperature - a temperature that can be found in
a reactor core. HTGRs - high temperature gas reactors operate at temperatures high
enough so that the graphite is continually annealing and one doesn't have problems with
a build-up of Wigner energy.

Dr. Gregory Greenman
Physicist
 
  • #4
Thanks Astronuc and Dr. Gregory greenman
 

What is the Wigner Effect in Metals?

The Wigner Effect in Metals refers to the phenomenon where the mechanical properties of a metal, such as its ductility and strength, deteriorate over time when exposed to high levels of radiation.

How does the Wigner Effect occur?

The Wigner Effect occurs when high-energy particles, such as neutrons, bombard a metal and displace its atoms from their original positions. These displaced atoms can then form clusters or defects, which can lead to changes in the mechanical properties of the metal.

What are the main factors that contribute to the Wigner Effect?

The main factors that contribute to the Wigner Effect are the type and energy of the radiation, the temperature of the metal, and the duration of exposure to radiation.

What are the potential consequences of the Wigner Effect in metals?

The consequences of the Wigner Effect in metals can include reduced ductility and strength, increased brittleness, and changes in the microstructure of the metal. This can ultimately lead to structural failures and safety hazards in nuclear reactors and other high-radiation environments.

How can the Wigner Effect be mitigated?

The Wigner Effect can be mitigated through various methods, such as using radiation-resistant materials, controlling the temperature and exposure time of the metal, and implementing regular inspections and maintenance to detect and repair any damage caused by radiation exposure.

Similar threads

  • Nuclear Engineering
Replies
1
Views
869
Replies
2
Views
735
  • Nuclear Engineering
Replies
10
Views
5K
  • Nuclear Engineering
Replies
2
Views
2K
Replies
6
Views
4K
  • Materials and Chemical Engineering
Replies
10
Views
7K
  • Advanced Physics Homework Help
Replies
1
Views
2K
  • Science and Math Textbooks
Replies
19
Views
17K
Replies
7
Views
4K
  • Astronomy and Astrophysics
Replies
2
Views
4K
Back
Top