Preparation of Chromium doped uranium nitride via Sol-Gel and Carbothermic reduction

Uranium nitride (UN) has been proposed as an accident tolerant fuel due to its enhanced thermal properties compared to the standard UO2. However, due to its low oxidation resistance, its implementation in water cooled reactors has not been allowed. A method to improve the corrosion resistance involves doping with oxide scale forming elements such as aluminum or chromium. In this work, UN microspheres were produced by an internal gelation method followed by carbothermic reduction and nitridation. Chromium was added as dopant in the solution to produce a homogenous mixture with uranium. The ternary phase (U2CrN3) was observed for the first time in Cr-doped UN microspheres produced via sol-gel and carbothermic reduction. Materials with and without the ternary phase were produced, and a mechanism of reaction was proposed. Chromium precipitations were also observed on the surface of the microspheres produced, indicating low solubility of Cr compounds in the UN matrix. ICP-MS and XRF measurements showed that Cr content is reduced after heating treatments, probably due to evaporation. Additionally, these results showed that Cr in the ternary phase is completely soluble in aqua regia, unlike the Cr in the material without the ternary phase

Second asymptomatic carotid surgery trial (ACST-2) : a randomised comparison of carotid artery stenting versus carotid endarterectomy

Background: Among asymptomatic patients with severe carotid artery stenosis but no recent stroke or transient cerebral ischaemia, either carotid artery stenting (CAS) or carotid endarterectomy (CEA) can restore patency and reduce long-term stroke risks. However, from recent national registry data, each option causes about 1% procedural risk of disabling stroke or death. Comparison of their long-term protective effects requires large-scale randomised evidence. Methods: ACST-2 is an international multicentre randomised trial of CAS versus CEA among asymptomatic patients with severe stenosis thought to require intervention, interpreted with all other relevant trials. Patients were eligible if they had severe unilateral or bilateral carotid artery stenosis and both doctor and patient agreed that a carotid procedure should be undertaken, but they were substantially uncertain which one to choose. Patients were randomly allocated to CAS or CEA and followed up at 1 month and then annually, for a mean 5 years. Procedural events were those within 30 days of the intervention. Intention-to-treat analyses are provided. Analyses including procedural hazards use tabular methods. Analyses and meta-analyses of non-procedural strokes use Kaplan-Meier and log-rank methods. The trial is registered with the ISRCTN registry, ISRCTN21144362. Findings: Between Jan 15, 2008, and Dec 31, 2020, 3625 patients in 130 centres were randomly allocated, 1811 to CAS and 1814 to CEA, with good compliance, good medical therapy and a mean 5 years of follow-up. Overall, 1% had disabling stroke or death procedurally (15 allocated to CAS and 18 to CEA) and 2% had non-disabling procedural stroke (48 allocated to CAS and 29 to CEA). Kaplan-Meier estimates of 5-year non-procedural stroke were 2·5% in each group for fatal or disabling stroke, and 5·3% with CAS versus 4·5% with CEA for any stroke (rate ratio [RR] 1·16, 95% CI 0·86-1·57; p=0·33). Combining RRs for any non-procedural stroke in all CAS versus CEA trials, the RR was similar in symptomatic and asymptomatic patients (overall RR 1·11, 95% CI 0·91-1·32; p=0·21). Interpretation: Serious complications are similarly uncommon after competent CAS and CEA, and the long-term effects of these two carotid artery procedures on fatal or disabling stroke are comparable