New burst criteria, axial fuel relocation and fission gas release options in the DRACCAR code

International audienceThe DRACCAR code has been developed at IRSN since 2006 and aims to simulate the 3D thermo-mechanical deformation and reflooding of a fuel rod assembly during a LOCA transient [1, 2]. Axial fuel relocation impact on peak cladding temperature and core coolability strongly depends on cladding mechanical behavior. Indeed ballooning and burst prediction is essential to evaluate axial power redistribution and blocking ratio of fluid sub-channels. Therefore cladding creep and burst have to be carefully modeled in LOCA codes. New Zy-4 burst criteria based on computations using neural networks [3] have recently been implemented in DRACCAR. Comparison with other available usual burst criteria (stress, strain, …) on Halden LOCA tests simulations will be presented. Then, new options have been developed to take into account fission gas release contribution to rod internal pressure. Sensitivity studies on fission gas release and other important parameters are performed to improve some Halden LOCA tests modelling with DRACCAR. Finally, new models in the axial fuel relocation module are detailed and code to experiment comparisons are presented and analyzed

New burst criteria, axial fuel relocation and fission gas release options in the DRACCAR code

International audienceThe DRACCAR code has been developed at IRSN since 2006 and aims to simulate the 3D thermo-mechanical deformation and reflooding of a fuel rod assembly during a LOCA transient [1, 2]. Axial fuel relocation impact on peak cladding temperature and core coolability strongly depends on cladding mechanical behavior. Indeed ballooning and burst prediction is essential to evaluate axial power redistribution and blocking ratio of fluid sub-channels. Therefore cladding creep and burst have to be carefully modeled in LOCA codes. New Zy-4 burst criteria based on computations using neural networks [3] have recently been implemented in DRACCAR. Comparison with other available usual burst criteria (stress, strain, …) on Halden LOCA tests simulations will be presented. Then, new options have been developed to take into account fission gas release contribution to rod internal pressure. Sensitivity studies on fission gas release and other important parameters are performed to improve some Halden LOCA tests modelling with DRACCAR. Finally, new models in the axial fuel relocation module are detailed and code to experiment comparisons are presented and analyzed

Prone Positioning During Extracorporeal Membrane Oxygenation in Patients With Severe ARDS

International audienceImportance Prone positioning may improve outcomes in patients with severe acute respiratory distress syndrome (ARDS), but it is unknown whether prone positioning improves clinical outcomes among patients with ARDS who are undergoing venovenous extracorporeal membrane oxygenation (VV-ECMO) compared with supine positioning. Objective To test whether prone positioning vs supine positioning decreases the time to successful ECMO weaning in patients with severe ARDS supported by VV-ECMO. Design, Setting, and Participants Randomized clinical trial of patients with severe ARDS undergoing VV-ECMO for less than 48 hours at 14 intensive care units (ICUs) in France between March 3, 2021, and December 7, 2021. Interventions Patients were randomized 1:1 to prone positioning (at least 4 sessions of 16 hours) (n = 86) or to supine positioning (n = 84). Main Outcomes and Measures The primary outcome was time to successful ECMO weaning within 60 days following randomization. Secondary outcomes included ECMO and mechanical ventilation–free days, ICU and hospital length of stay, skin pressure injury, serious adverse events, and all-cause mortality at 90-day follow-up. Results Among 170 randomized patients (median age, 51 [IQR, 43-59] years; n = 60 women [35%]), median respiratory system compliance was 15.0 (IQR, 10.7-20.6) mL/cm H 2 O; 159 patients (94%) had COVID-19–related ARDS; and 164 (96%) were in prone position before ECMO initiation. Within 60 days of enrollment, 38 of 86 patients (44%) had successful ECMO weaning in the prone ECMO group compared with 37 of 84 (44%) in the supine ECMO group (risk difference, 0.1% [95% CI, −14.9% to 15.2%]; subdistribution hazard ratio, 1.11 [95% CI, 0.71-1.75]; P = .64). Within 90 days, no significant difference was observed in ECMO duration (28 vs 32 days; difference, −4.9 [95% CI, −11.2 to 1.5] days; P = .13), ICU length of stay, or 90-day mortality (51% vs 48%; risk difference, 2.4% [95% CI, −13.9% to 18.6%]; P = .62). No serious adverse events were reported during the prone position procedure. Conclusions and Relevance Among patients with severe ARDS supported by VV-ECMO, prone positioning compared with supine positioning did not significantly reduce time to successful weaning of ECMO. Trial Registration ClinicalTrials.gov Identifier: NCT0460755