ASME STP-NU-037

Abstract

<em><strong>Part I - Review of Current Operating Conditions Allowable Stresses in ASME Section III Subsection NH and Overview of the Availability of the Original and Augmented Databases Needed to Establish So, S_t, and S_r</strong></em> <br>The current operating condition allowable stresses provided in ASME Section III, Subsection NH were reviewed for consistency with the criteria used to establish the stress allowables and with the allowable stresses provided in ASME Section II, Part D. It was found that the So values in ASME IIINH were consistent with the S values in ASME II-D for the five materials of interest. However, it was found that 0.80Sr was less than S_o for some temperatures for four of the materials. Only values for alloy 800H appeared to be consistent with the criteria on which So values are established. With the intent of undertaking a more detailed evaluation of issues related to the allowable stresses in ASME III-NH, the availabilities of databases for the five materials were reviewed and augmented databases were assembled. <br><em><strong>Part II and Part III - Assessment of the Databases Leading to the Establishment of Allowable Stresses in ASME Section III Subsection NH and Recommended Action for the Correction of Currently Listed Values for S_o, S_t and Sr</strong></em> <br>Based on a review of the current operating condition allowable stresses provided in ASME BPV Section III, Subsection NH and the finding of inconsistencies between the S values in ASME BPV Section II, Part D and the So values in ASME BPV III-NH for the five materials included in ASME BPV III-NH, expanded databases for stress-rupture, tertiary creep and time to 1% strain were assembled for use estimating and possibly revising the stress allowables in ASME BPV III-NH. A preliminary evaluation showed that, in spite of the substantially larger databases, the stress allowables St and Sr for some materials were within 5% of the existing values. It was judged that the existing values in ASME BPV III-NH for alloy 800H and 9Cr-1Mo-V steel were conservative and adequate for use in the temperature range of interest to the Generation IV reactor design. A number of issues were identified in using the databases to estimate the stresses based on tertiary creep and time to 1% strain criteria. Some actions were suggested to resolve the issues. The greatly expanded times for the databases were expected to help in extending allowable stresses to at least 500,000 hours.