Vessel annealing

In Finland the reactor pressure vessel at Loviisa-1 is to be annealed to remedy the embrittlement caused by neutron irradiation. The embrittlement can be detected by monitoring changes in the mechanical properties of the pressure vessel steel and welds from tensile test data, hardness and Charpy V-notch transition curves and fracture toughness results. Copper and phosphorus impurities may be the cause of the sensitivity to the neutron irradiation. The annealing programme - a week of heat treatment at 450oC - reduces the effect of irradiation on the shift of the brittle-ductile transition temperature. Other annealing programmes have taken place at the Bohunice and Marble Hill reactors and this may become a routine way of prolonging the life of the reactor. (UK)