Reactor vessel annealing to mitigate radiation effects

Neutron radiation in nuclear power reactors is known to degrade the properties of the reactor pressure vessel. A major concern is the loss in toughness in the beltline region which could require restrictions on the operation of the plant during heatup and cooldown, or if great enough, limit the life of the plant. Certain vessels with high copper containing welds degrade at an accelerated rate exacerbating the problem for those vessels. Further, this condition is potentially a factor in restricting life extension of nuclear plants beyond design life. Thermal annealing at temperatures well above the normal operating temperature of a reactor vessel is known to restore much of the original toughness properties. This paper discusses the current state of knowledge for in-place annealing of reactor vessels, potential problems associated with such annealing and issues that might be necessary to resolve for reactor operation subsequent to thermal annealing