The common approach to safety in a nuclear power plant is to design the system to respond safely to a large postulated accident, the so-called design basis accident. Accidents more severe than the design basis accident (“severe accidents”) are assessed but the system is not designed to withstand them; they are considered too unlikely to require specific design actions. For the pressurised-water reactor (PWR), the design basis accident (DBA) is the Large Break Loss-of-Coolant Accident (LB-LOCA), in which it is assumed that one of the large inlet coolant pipes from the circulating pump to the reactor vessel is completely broken and moves apart to allow free discharge of the primary coolant from both broken ends. For this type of break total coolant loss will occur in 100s or less. Although the reactor is by this time sub-critical so that little power is produced from fission, a large amount of decay power exists and causes the fuel rod claddings to have a temperature in the region of 600–800 °C. This paper describes experimental investigations designed and performed in order to provide detailed information about the macroscopic behaviour of the steam-water flow occurring during the reflood phase following a PWR LB-LOCA. Specifically, a bottom-up rewetting process was studied, in which water droplets may be entrained in the vapour flow and contribute to cooling of the hot fuel pin before it is quenched. In these experiments the test section is initially preheated to temperatures up to 600 °C and then quenched by introducing water at the bottom of the tube at atmospheric pressure. During the course of this transient process axial temperature and heat flux profiles will be recorded, extending the existing databank of cases for code validation. Simultaneously, an axial viewing technique will be applied to observe the quench front, and any pre-cursory droplet production, occurring during these singletube reflood experiments. As part of the preliminary validation of this novel technique, a series of air-water vertical upflow conditions have been examined. The results of these preliminary studies provide detailed visualisation of typical entrainment processes likely to be encountered during single-tube reflood.
Objective: To determine whether pars plana vitrectomy (PPV) combined with the internal limiting membrane (ILM) peeling technique improves the anatomic and functional outcomes of refractory diabetic macular oedema (DME) in comparison with PPV alone.
Methods: All relevant articles published in English were retrieved from PubMed, google scholar, web of Science, scopes, and Cochrane library databases between January 1st 1990 and September 28 2022. The meta-analysis was conducted using the Statistical software R 4.2.2.
Results: Among 709 articles that were initially identified, 10 studies involving 1126 eyes with DME were found to be eligible for this meta-analysis and systematic review. Our results revealed that postoperative best corrected visual acuity (BCVA) was better in the non-peeling group than in the ILM peeling group (MD=-0.08, 95% CI: -0.12, -0.04, p<0.001), the improvement of BCVA was not significant between the two groups (RD=5.59, 95% CI: -4.81, 15.99, p=0.13). The random effects model showed that changes in central macular thickness were not significantly different between the ILM peeling group and the non-ILM peel group (MD=23.10, 95% CI: -53.82, 100.02, p=0.56).
Conclusion: The functional and morphological clinical outcomes in the non-inferior group are equal to that of the ILM peeling group. Yet, further large-scale prospective, randomized, controlled trials are warranted to further validate the reported results.
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