Surveillance capsule results from Oconee Nuclear Station Units 1, 2 and 3

The first capsules of the reactor vessel surveillance programme of Oconee Nuclear Station Units 1, 2 and 3 were removed and evaluated after the first cycle of operation to verify neutron fluence calculations and to confirm the predictive techniques used to evaluate the irradiation response of the vessel's weld and shell materials. Fluence calculations based on dose meter evaluation demonstrated that the generic design curve was conservative and that the degree of conservatism could be reduced for future designs. Projection of current data, assuming equilibrium cycle and no change in fuel or reactor operating scheme, shows that the end-of-life fluence value at the pressure vessel inside surface will be approximately one half of the generic value. The changes in Charpy impact data, as measured by the change in RTsub(NDT) and the decrease in upper shelf energy, were compared with values obtained by procedures described in Regulatory Guide 1.99. At the very low neutron fluences where the mechanical properties of the irradiated material have not changed significantly, the actual shift measured at 35MLE is larger than the shift measured at 50ftlbf. This relationship might be reasoned because the normal relationship between energy absorption, yield strength, and lateral expansion indicates that for a given lateral expansion value, the corresponding energy absorption increases as yield strength increases. For higher neutron fluence values, it is expected that the difference between the shifts at 50ftlbf and at 35MLE will be greater. Consequently, the change in RTsub(NDT) will be controlled by the change in 35MLE temperature. (author)