A pressure vessel surveillance program requires a methodology for relating radiation-induced changes in materials exposed in accelerated surveillance locations to the condition of the pressure vessel (see Practice E853). An important consideration is that the irradiation exposures be expressed in a unit that is physically related to the damage mechanisms.
A major source of neutron radiation damage in metals is the displacement of atoms from their normal lattice sites. Hence, an appropriate damage exposure index is the number of times, on the average, that an atom has been displaced during an irradiation. This can be expressed as the total number of displaced atoms per unit volume, per unit mass, or per atom of the material. Displacements per atom is the most common way of expressing this quantity. The number of dpa associated with a particular irradiation depends on the amount of energy deposited in the material by the neutrons, and hence, depends on the neutron spectrum. (For a more extended discussion, see Practice E521.)
No simple correspondence exists in general between dpa and a particular change in a material property. A reasonable starting point, however, for relative correlations of property changes produced in different neutron spectra is the dpa value associated with each environment. That is, the dpa values themselves provide a spectrum-sensitive index that may be a useful correlation parameter, or some function of the dpa values may affect correlation.
TABLE 1 ENDF/B-VI-based Iron Displacement Cross Section
| Bin | EngA (MeV) | σd (barns) | Bin | EngA (MeV) | σd (barns) | Bin | EngA (MeV) | σd (barns) |
|---|---|---|---|---|---|---|---|---|
| 1 | 0.100E-09 | 158.3543 | 2 | 0.1050E-09 | 154.6209 | 3 | 0.110E-09 | 151.1395 |
| 4 | 0.1150E-09 | 147.8895 | 5 | 0.120E-09 | 144.1054 | 6 | 0.1275E-09 | 139.9202 |
| 7 | 0.1350E-09 | 136.0860 |
ASTM E693-12 history
Copyright ©2024 All Rights Reserved | |||||