Effect of test-caused degradation on the unavailability of standby safety components

This paper proposes a safety-critical standby component unavailability model that contains aging effects caused by the elapsed time from installation, component degradation due to surveillance tests, and imperfect maintenance actions. An application of the model to a Motor-Operated Valve and a Motor-Driven Pump involved in the HPIS of a VVER/1000-V446 nuclear power plant is demonstrated and compared with other existing models at component and system levels. In addition, the effects of different unavailability models are reflected in the NPP&amp;apos;s risk criterion, i.e., core damage frequency, over five maintenance periods. The results show that, compared with other models that do not simultaneously consider the full effects of degradation and maintenance impacts, the proposed model realistically evaluates the unavailabilities of the safety-related components and the involved systems as a plant age function. Therefore, it can effectively reflect the age-dependent CDF impact of a given testing and maintenance policy in a specified time horizon.Full text license: CC BY</p

Meta-Analysis of Coronary Bypass Graft Patency Assessment With Invasive vs Computed Tomographic Angiography

BACKGROUND: Computed tomography (CT) coronary angiography has emerged as a non-invasive alternative for evaluating graft patency after coronary artery bypass grafting (CABG), but there is ongoing debate regarding its diagnostic performance compared to invasive coronary angiography, particularly for arterial and composite grafts. METHODS: MEDLINE, Embase, and Cochrane databases were searched to identify studies comparing CT coronary angiography to invasive coronary angiography for detection of graft occlusion in post-CABG patients. Outcomes included sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy. Meta-regression explored key modifiers. Pooled estimates were calculated using random-effects models, with heterogeneity measured via I2. RESULTS: Fifty studies met inclusion criteria, including 3,449 patients (25% women). CT coronary angiography sensitivity for graft occlusion was 0.96 (I2 = 48%), specificity was 0.97 (I2 = 46%), positive predictive value was 0.94 (I2 = 62%), negative predictive value was 0.98 (I2 = 41%) and overall diagnostic accuracy was 0.97 (I2 = 58%). The pooled incidence rate of graft occlusion across 7,506 included grafts was 0.08 per graft-year (PGY) (95% CI: 0.06-0.10) using a random-effects model, and 0.07 PGY (95% CI: 0.07-0.08). At meta-regression, study year, sample size, β-blocker use, number of slices, and time since surgery, but not type and configuration of CABG grafts, were significantly associated with CT coronary angiography sensitivity. CONCLUSIONS: CT coronary angiography detects coronary artery bypass graft occlusion with a high degree of sensitivity and specificity independently of graft type and configuration and can be used for imaging of every type of CABG graft.2026-07-0