Estimation of master curve based RT To reference temperature from CVN data

The ASME code cases N-629 and N-631 permits the use of a Master Curve-based index temperature (RT To=T 0+19.4°C) as an alternative to traditional RT NDT-based methods of positioning the ASME K Ic and K IR curves. This approach was adopted to enable use of Master Curve technology without requiring the wholesale changes to the structure of the ASME Code that would be needed to use all aspects of Master Curve technology. For the brittle failure analysis considering irradiation embrittlement additionally a procedure to predict the adjustment of fracture toughness for EOL from irradiation surveillance results must be available as by NRC R.G. 1.99 Rev. 2 e.g.: ART = Initial RT NDT + RT NDT + Margin. The conservatism of this procedure when RT NDT is replaced by RT To is investigated for western nuclear grade pressure vessel steels and their welds. Based on a systematic evaluation of nearly 100 different irradiated material data sets, a simple relation between RT Toirr, RT Tore f and T 41JRG is proposed. The relation makes use of the R.G. 1.99 Rev. 2 and enables the minimizing of margins, necessary for conventional correlations based on temperature shifts. As an example, the method is used to assess the RT To as a function of fluence for several German pressure vessel steels and corresponding welds. It is shown that the method is robust and well suited for codification. Copyright