Radiation Damage - Environmental Degradation of Metals - page 469

Table 9.1 [1] lists some of the materials, irradiation temperatures, and pro-
jected end-of-life neutron fluences for various components in light water reactors
(LWRs), liquid metal fast-breeder reactors (LMFRs), and controlled thermonu-
clear reactors (CTRs). The wide range of temperatures and fluences encountered
in these reactors is detrimental to the mechanical properties of the components
involved and such damages are directly related to the irradiation-induced point
defects.

9.2 RADIATION-INDUCED DEFECT PRODUCTION
Defect production in metals is associated with the displacement of atoms from
lattice sites. It is difficult to achieve in research studies the irradiation conditions
with fast neutrons encountered in reactors, and it takes several years of reactor
irradiation to test a material to the target fluence. However, electron and ion
irradiations are used to quickly achieve the equivalent of very long exposures
to fast-fission reactor neutrons. Computer simulation and experimental field ion
microscopy have provided a qualitative picture of the irradiation-induced defect
production. The sequence of events is illustrated in Fig. 9.1 [2]. The PKA is
dislodged by a neutron collision. It in turn dislodges other atoms. The net result
is a localized region (typically

10 ˚ ), termed a depleted zone or displacement
cascade , in which a large fraction of the atoms are missing, thereby resulting in
a high density of vacancies. It is the displacement cascade which dissipates the

Figure 9.1 Schematic representation of radiation damage. P denotes the position where
the primary knock-on atom comes to rest. (From Ref. 2)