THERMAL ANNEALING OF WWER-440 NUCLEAR REACTOR PRESSURE VESSEL INTERNALS MATERIAL

Current trend of long-term operation of NPP's for more than 60 years requires assurance of its safety and reliability. One of the solutions how to extend service life of reactor pressure vessel (RPV) is thermal annealing, which became a verified technology and its application in nuclear industry was prompted mainly due to an inability of RPV exchange. At present time, there is no comparable method for RPV internals that are not monitored by surveillance program and their material is exposed to significantly more intense neutron flux than the RPV. Paper presents the thermal annealing as one of the possible solutions to provide and re-establish sufficient mechanical properties of RPV internals during the operation. According to previously obtained results of unirradiated material, two thermal annealing regimes for irradiated experimental material were selected based on the annealing temperatures of 550 and 600 degrees C. The possibility of recovery of mechanical properties to the level almost corresponding to the initial state by the thermal annealing was studied by hardness testing and static fracture toughness tests before and after the thermal annealing of irradiated material.