Effect of Embrittlement Trend Curve Model on the Reference Temperature Based Screening Limits for Pressurized Thermal Shock

Abstract

Recently, the USNRC has proposed a voluntary alternative to the pressurized thermal shock (PTS) rule (10CFR50.61(a)) that may be used instead of the existing PTS rule (10CFR50.61) by power reactor licensees to demonstrate the safety of their RPVs. The reference temperature (RT) screening limits in 10CFR50.61(a) are less restrictive than those of 10CFR50.61; this relaxation being justified by the much more realistic models that underlie the technical basis of the revised rule. One of the many models that constitute this technical basis is used to estimate the effect of irradiation damage on the fracture toughness transition temperature. This relationship, which is called the embrittlement trend curve, or ETC, can change as time goes on due to the continued development of new knowledge (e.g., from on-going reactor vessel surveillance programs, from test reactor studies aimed at better understanding the physical mechanisms of irradiation damage, etc.). In this paper we present information that quantifies the effect of different ETCs on the through wall cracking frequencies that are calculated using the probabilistic fracture mechanics computer code that was used to establish the RT limits that have been proposed in 10CFR50.61(a).

Influence Factors of Fracture Mechanics Analysis of Reactor Pressure Vessel under Pressurized Thermal Shock

“…The fracture mechanics analysis of defective RPV under PTS events is performed by linear elastic fracture mechanics [2]. The brittle fracture criterion based on linear elastic fracture mechanics mainly adopts the stress intensity factor theory, and the type I crack is the most dangerous in the three failure modes of cracks.…”

Verification of probabilistic fracture mechanics analysis code PASCAL for reactor pressure vessel

“…2(a) was analyzed, with its depth a = 6.5 mm and aspect ratio 2c/a = 10. A stuck-open valve (SOV) transient (EricksonKirk et al, 2006) was considered in Case-A. The time-history data of coolant water temperature and internal pressure during the SOV transient are shown in Fig.…”

“…2(b)) was analyzed with its crack depth 2a = 10.275 mm, aspect ratio c/a = 5 and distance d = 0.1 mm. In addition, a large break loss-of-coolant accident (LBLOCA) (EricksonKirk et al, 2006), with the time-varying coolant temperature and internal pressure shown in Fig. 3(b), was considered in this case.…”

“…Fig.3Time-history data for SOV and LBLOCA transients(EricksonKirk et al, 2006). The red and green lines represent the coolant water temperature and inner pressure, respectively.…”