CYCLE SPECIFIC EVALUATION OF THE MARGIN TO BALLOONING AND BURST OF HIGH BURNUP FUEL RODS DURING A LARGE BREAK LOSS-OF-COOLANT ACCIDENT

摘要

Loss-of-coolant accident (LOCA) experiments inHalden and Studsvik, with high burnup fuel, havedemonstrated fuel fragmentation, axial relocation anddispersion of fuel fragments through the burst opening ofthe fuel rod. Axial relocation and dispersal may be asafety issue that is not covered by today’s LOCAembrittlement criteria. One way of avoiding fuelfragmentation, relocation and dispersal is to limit thepower to avoid burst and ballooning. Vattenfall isdeveloping a methodology for this, in order to facilitatean quick assessment in connection with core design. Inthis paper, a cycle specific evaluation of the margin withrespect to average power, for the most limiting highburnup fuel rods in the core during a large break LOCA,is presented for one of the PWRs in Ringhals.Work is ongoing to find the burnup limit for fuelfragmentation, and in this paper, the fuel rods withaverage burnup above 60 MWd/kgU are investigated. Inthe evaluation FRAPCON 4.0p1, TRACE v5.0p4 andFRAPTRAN 2.0 are used. The fuel rod input parametersare calculated by FRAPCON based on the actual coredesign and power histories. The large break LOCA issimulated in TRACE and the ballooning and burst areevaluated in FRAPTRAN.