Uncertainty regarding radiation embrittlement at high fluence, indicative of extended operating life beyond 60 years for current operating pressurized water reactor (PWR) vessels, has been identified as a potential limiting degradation mechanism. There are limited U.S. power reactor surveillance data at fluences greater than about 4E19 n/cm2 (E > 1 MeV) currently available for comparison with existing embrittlement prediction models. Extended operating life to 80 years is projected to have vessel peak fluence approaching 1E20 n/cm2, for a small number of plants. The two current U.S. embrittlement models are contained in Nuclear Regulatory Commission (NRC) Regulatory Guide 1.99, Revision 2, and the Code of Federal Regulations, 10 CFR 50.61a. This paper compares the latest available high fluence power reactor surveillance data to the predictions of these two models, and to another model that has been proposed as better for high fluence data based on combined test reactor and power reactor data from sources extending beyond the U.S. These comparisons indicate the fluence ranges and material groups where the different models deviate from the measured data. The results from these comparisons have been used to select materials for a proposed new PWR supplemental surveillance program (PSSP) that utilizes previously tested irradiated surveillance specimens reconstituted and subsequently re-irradiated to higher fluences.

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