The Effect of Neutron Flux on Radiation-Induced Embrittlement in Reactor Pressure Vessel Steels

Abstract

The effect of neutron flux level is a longstanding concern for determining the applicability of test reactor data or high lead-factor surveillance data to the prediction of embrittlement in commercial reactor pressure vessels (RPV). However, as operating reactors reach higher fluences, the question of flux effects is becoming increasingly relevant for situations such as embrittlement attenuation through the (RPV) and the comparison of boiling and pressurized reactor RPVs. In spite of its technological importance and extensive experimental and theoretical investigation, the issue of neutron flux effects on radiation-induced embrittlement in RPV steels remains unresolved. For neutron fluxes much greater than RPV operating conditions (>100 times higher), a regime exists in which the effects of flux are well defined experimentally and are well predicted by current models. These same models predict that the effect of flux should be relatively weak for values near those obtained in commercial RPVs, but may increase at lower fluxes. However, it is difficult to obtain sufficient data at low to intermediate fluxes to unambiguously determine the effects of flux since the time required to reach the desired fluences is necessarily long. In order to demonstrate the potential effects of flux on RPV embrittlement, and to help interpret the available experiments, a kinetic embrittlement model has been used in an analysis of the primary variables involved. The results of the analysis are consistent with a modest effect of flux on embrittlement for fluxes near those typical of commercial RPVs.

Evolution of the nanostructure of VVER-1000 RPV materials under neutron irradiation and post irradiation annealing

“…A similar result was found for the precipitates in a low copper steel from the Chooz reactor [41]. The size of Cu-enriched precipitates increases under irradiation [42][43][44].…”

Nonlinear Ultrasonic Techniques to Monitor Radiation Damage in RPV and Internal Components

“…Recall that the JFL samples contained 0.01% Cu (low-copper steel), and the JRQ samples contained 0.14% Cu (medium-copper steel). It has been shown that the dominating hardening mechanism in low-copper steels are other defects such as point defect clusters and manganesenickel precipitates [13,19]. It is plausible that these defects, as well as UMDs as suggested in [13], have formed in the high fluence samples of the low-Cu JFL material, creating more pinning points for dislocations and thus causing a decrease in β, which would align with the experimental results.…”

“…The effect of higher fluxes typical of test reactors depends on the combination of copper content, irradiation temperature, and neutron fluence [13,19]. It has been shown that in low Cu steels, higher flux typical of test reactors can produce increased hardening at higher fluence due to an increased amount of unstable matrix defects (UMDs) [13].…”

A Review of the Application of Rate Theory to Simulate Vacancy Cluster Formation and Interstitial Defect Formation in Reactor Pressure Vessel Steel

“…Rate theory is one method of computational simulation that can address this issue and develop radiation-induced hardening models. Neutron flux and dose levels in the operational range (low to intermediate) are of particular concern, and data is not well determined [60]. Thus, illustrating the radiation effects becomes increasingly difficult.…”

“…− 10 !!! / ) [60]. Typical surveillance experiments for embrittlement often result in 3-5 times greater flux than the maximum observed RPV flux; similarly material sensitivity to radiation is generally analyzed at 10 to 1000 times greater flux [60].…”