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The U.S. Nuclear Regulatory Commission (NRC) and the Electric Power Research Institute (EPRI) are working cooperatively under a memorandum of understanding to validate welding residual stress (WRS) predictions in pressurized water reactor (PWR) primary cooling loop components containing dissimilar metal (DM) welds. These stresses are of interest as DM welds in PWRs are susceptible to primary water stress corrosion cracking (PWSCC) and tensile weld residual stresses are the primary driver of this degradation mechanism. The NRC/EPRI weld residual stress (WRS) analysis validation program consists of four phases, with each phase increasing in complexity from laboratory size specimens to component mock-ups and cancelled-plant material. This paper discusses Phase 2 of the WRS characterization program involving an international round robin analysis project in which participants analyzed a prototypic reactor coolant pressure boundary component. Mock-up fabrication, WRS measurements and comparison with predicted stresses through the DM weld region are described. The results of this study show that, on average, analysts can develop WRS predictions that are a reasonable estimate for actual configurations as quantified by measurements. However, the scatter in predicted results from analyst to analyst can be quite large. For example, in this study, the scatter in WRSs through the centerline of the main DM weld (prior to stainless steel weld application) predicted by analysts is approximately +/− 200 to 300 MPa at 3 standard deviations for axial stresses and +/− 300 to 400 MPa at 3 standard deviations for hoop stresses. Sensitivity studies that vary important parameters, such as material hardening behavior, can be used to bound such large variations.

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The hardness of various types of soot produced by heavy‐ and light‐duty diesel engines of European, Japanese, and North American designs was measured by low‐loss electron energy‐loss spectroscopy (EELS). No clear general trend can be established that shows heavy‐duty diesel engine soot is necessarily harder than light‐duty diesel engine soot. The variation in hardness among individual soot particles produced by the same diesel engine can be as large as differences between the hardest soot particles produced by heavy‐duty diesel engines and the softest soot particles produced by light‐duty diesel engines. There are heavy‐duty diesel engines that can produce soot that is softer than that produced by some light‐duty diesel engines and vice versa. Nevertheless, the hardness of all types of soot studied is close to the range of hardness of metal engine parts. Thus, the results indicate that soot is hard enough to abrade some metal engine parts.