Environmental Engineering Reference
In-Depth Information
9
Radiation Damage
9.1 INTRODUCTION
Irradiation of metals and alloys with energetic particles generates point defect
clusters, phase transformation, and chemical reaction (transmutation) products
that individually or combinedly bring about changes in the mechanical properties
of the materials and dimensional changes in the metallic components. Radiation
damage manifests itself in the following forms:
1. Irradiation growth
2. Void swelling
3. Radiation-enhanced creep, and
4. Irradiation strengthening and embrittlement
The study of radiation damage has assumed importance with the development
of fast-breeder reactors for the production of nuclear energy. Whereas a thermal
neutron diffuses through a metal without displacing lattice atoms, a fast neutron
collides with the lattice atoms to produce energetic primary knock-on atoms
(PKA), many with tens of thousands of electron volts of energy. Each of the
energetic primaries produces a cascade of displacements, resulting in a number
of vacancies and interstitials. The damage level is specified by the term ''displace-
ments per atom'' (dpa), which is the average number of times that a lattice atom
has been displaced during irradiation, and the damage rate is given as dpa-s
1
.
Some core components of a commercial fast-breeder reactor are expected to reach
a damage level of 2000 dpa during their reactor life.
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