Experimental results of the commissioning bundle test QUENCH-L0 performed in the framework of the QUENCH-LOCA program

The QUENCH-L0 experiment was defined as commissioning test for the new QUENCH-LOCA test series. The overall objective of this bundle test series is the investigation of ballooning, burst and secondary hydrogen uptake of the cladding under representative design basis accident conditions as well as detailed post-test investigation of cladding mechanical properties to check the embrittlement criteria. The QUENCH-L0 test bundle contained 21 electrically heated rod simulators with Zircaloy-4 claddings. Each rod was separately pressurized with krypton gas with initial pressures of 35, 40, 45, 50, and 55 bar for different rods. The transient phase with heating from 793 K to 1343 K lasted 185 s. The increased ductility of the heated cladding resulted in a progressive ballooning and consequent burst of all of the pressurized rods during the transient. The test was terminated by water quenching of the bundle without usual intermediate slow cooling phase. Post-test investigations showed strain values between 20 and 35% at cladding positions with oxidation degree corresponding to 2% ECR. Neutron radiography of cladding tubes revealed elevated concentration of absorbed hydrogen in cladding regions near to burst positions. During the tension test the cladding tubes were ruptured mostly at the middle position of burst. (authors)