Impact of Using ASME Section XI Code Case N-830 on Plant Heatup and Cooldown Pressure-Temperature Limit Curves for Pressurized Water Reactors

摘要

Nuclear plant reactor pressure vessel heat-up and cool-down pressure temperature (P-T) limit curves are determined using ASME Section XI, Appendix G. ASME has adopted into ASME Section XI Appendix G the allowable use of the ASTM E1921 master curve fracture toughness based reference temperature (T_0) to index the K_(Ic) curve. ASME Section XI Code Case N-830 allows the use of the K_(Jc) 95% lower bound master curve indexed using T_0 directly. In ASME Section XI Appendix G, the equation RTT_0 = T_0 + 19.4°C, as an alternate RT_(NDT), shifts the K_(Ic) curve to approximate the K_(Jc) 95% lower bound master curve, however, the K_(Ic) exponential curve parameters are different. Thus, this paper evaluates the impact on plant heatup and cooldown pressure-temperature limit curves between the two ASME approved methods for typical pressurized water reactors (PWR). Different degrees of embrittlement are assessed to determine differences in the two approaches on reactor pressure vessel (RPV) beltline operating curves. Furthermore, in the proposed Revision 19 of Regulatory Guide 1.147, the US NRC has included a condition on the use of Code Case N-830 that prohibits the use of the current K_(Ic) equation in ASME Section XI Appendix G when these values are above the K_(Jc) lower bound 95% curve at temperatures below T_0 - 64°C. This paper briefly discusses this NRC condition on the P-T limit curves.