The characteristics of reactor materials are affected by the irradiation in the reactor.
To investigate these effects, specimens are retrieved after the irradiation and receive the post-irradiation test. This test is conducted to survey the change in material characteristics of the reactor vessel in service. Specimens for surveillance are fitted in the reactor vessel to receive similar irradiation that the nuclear power plant is exposed during the actual operation. These specimens are retrieved at a specified interval and the destructive inspection is performed.