The lifespan of nuclear reactor pressure vessels

The main degradation mechanisms of a PWR reactor pressure vessel is irradiation embrittlement. The limiting criterion will be either the RTNDT of the inside surface of the vessel, submitted to the maximum neutron flux, or the decrease in upper shelf energy level (mainly for older US plants). For older pressure vessels, this embrittlement could reduce the life of the vessel, and when a high embrittlement is expected, a flux reduction program implemented soon enough could be an effective mitigating measure. When no other solution is available, an anneal of the pressure vessel seems to be feasible and would allow to restore partially its properties. (author) 8 figs., 1 tab., 13 refs