Neutron embrittlement of reactor pressure vessel steels: a challenge to positron annihilation and other methods

The deterioration of the mechanical properties of reactor pressure vessel (RPV) steels during their irradiation in a nuclear power plant is known as neutron embrittlement. This is of great importance for safety considerations to avoid any failure of the RPV. The only known possibility to improve the mechanical properties of a neutron embrittled RPV is to anneal it thermally. Usually the assessment of irradiation sensitivity and thermal annealing behaviour will be performed by means of destructive test methods, mainly the impact and tension test. A new kind of search is presented for an efficient temperature-time-regime for post-irradiation thermal heat treatment using nondestructive test methods like positron annihilation and hardness and proof the recovery of mechanical properties by destructive test methods. (author)