Effects of Radiation Damage
The previously discussed changes in microstructure due to radiation damage affect the macroscopic, mechanical properties of the material. These effects happen for a variety of reasons, but are generally less noticeable at higher temperatures as the damage caused by radiation is constantly being annealed out: at higher temperatures vacancy and interstitial mobility are increased so they are removed from the lattice faster.
The following table gives an overview of the effects observed.
|Material Property||Effect of Radiation Damage|
|Yield strength||Increases on irradiation, along with a decrease in plastic flow range.|
|Ultimate tensile strength||This also increases on irradiation, but less than the yield strength.|
|Ductile-brittle transition temperature||This marks the transition between a material exhibiting ductile behaviour at higher temperatures and brittle behaviour at lower temperatures. It increases significantly on irradiation, which can present a problem when the reactor vessel cools on shut down when internal pressure within the reactor is still high, and so fracture can occur if this is not taken into account.|
|Young’s modulus||Small increase on irradiation.|
|High-temperature creep rate||Increase during irradiation.|
|Density||Decrease as the material swells on irradiation.|
|Thermal conductivity||Decrease on irradiation since lattice disorder increases, thus increasing phonon scattering.|
|Electrical conductivity||Decrease for similar reasons to thermal conductivity.|
The following sketch shows the stress-strain curve for a typical steel and its different form after irradiation.
|A stress-strain curve for a stainless steel irradiated or not.|