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Assessments of the hardening and embrittlement of pressure vessel steels and welds as a function of neutron dose use trend curves derived from surveillance programs and accelerated irradiation data. A temperature dependent factor is incorporated for assessing vessel locations operating at different temperatures. As hardening and embrittlement arise from the sum of matrix damage and copper impurity precipitation, the influence of irradiation temperature on each process needs to be established. For irradiations performed below {approximately} 300 C recent data shows that the dose-dependent growth of copper precipitates ceases at a mean diameter of about 2 nm that also corresponds to peak hardening and embrittlement by copper. For doses beyond this peak copper dose the property-dependence on irradiation temperature can be identified with that of matrix damage alone. An analysis of several experiments on plate steels, performed at differing irradiation temperatures, has permitted the temperature dependence of matrix hardening to be defined by the simple empirical factor F{sub T} = 1.869 {minus} 4.57 {times} 10{sup {minus}3} T where T is the irradiation temperature. When a linear correlation between irradiation hardening and embrittlement is observed, then F{sub T} can be used to analyze the temperature dependence of matrix embrittlement. The validity ofmore » using F{sub T} in successfully correlating irradiation results has been demonstrated for several plate steels and welds with differing copper contents.« less |
