Best　estimate　plus　uncertainty　methodology　is　an　advanced　technology　for　licensing　application　of　the　nuclear　power　plants,　but　some　aspects　can　still　be　improved　in　the　conventional　input-driven　methodologies.　For　instance,　uncertainties　of　the　closure　models　are　not　properly　handled;　local　sensitivity　analysis　methods　not　suitable　for　complex　nuclear　systems　are　still　widely　utilized;　the　sensitivity　analysis　process　needs　to　be　performed　again　every　time　new　parameters　are　identified.　Optimization　researches　were　carried　out　in　the　study.　A　structural　method　was　proposed　to　quantify　the　uncertainties　of　the　closure　models,　and　a　low-cost　moment-independent　global　sensitivity　analysis　method　was　developed　to　improve　the　sensitivity　analysis　framework.　By　integrating　the　improvements　into　the　conventional　input-driven　framework,　an　uncertainty　method　with　model　treatment　and　improved　sensitivity　analysis　was　obtained.　Finally,　the　method　was　validated　through　a　large　break　loss　of　coolant　accident　in　a　three-loop　pressurized　water　reactor.　©　2020　Elsevier　Ltd