Results of the bundle test QUENCH-19 with FeCrAl claddings

The QUENCH-19 bundle experiment was the worldwide first bundle test simulating severe accident conditions with ATF cladding materials. It was conducted with FeCrAl(Y) cladding tubes (alloy B136Y3, developed by the Oak Ridge National Lab, USA) and 4 Kanthal AF spacer grids as well as 7 Kanthal APM corner rods and Kanthal APM shroud was conducted at KIT on 29th August 2018. All Kanthal materials used are made of FeCrAl alloys too. The test objective was the comparison of FeCrAl(Y) and ZIRLO™ claddings under similar electrical power and gas flow conditions. The experiment was performed in four stages. The electrical power supply was the same as in the reference test QUENCH-15 (ZIRLO) during the first two stages (pre-oxidation and transient). The third stage with constant electrical power was performed to extend the temperature increase period. The test was terminated at peak cladding temperature of about 1800 K by water flooding similar to QUENCH-15 (stage four). As expected, the hydrogen release during this test with FeCrAl cladding was significantly lower than for the reference test QUENCH-15 with ZIRLO cladding tubes. The total hydrogen production was 9.2 g (47.6 g for QUENCH-15), even the test duration at maximum power input was 2000 s longer. The post-test observation of the bundle showed the damage of several claddings at the bundle elevations between 850 and 1000 mm. The claddings failed either due to interaction with melted thermocouples (mostly) or by spalling of small annular cladding parts. Furthermore, unexpectedly some rods circumferentially broke most probably during reflood due the larger coefficients of thermal expansion of FeCrAl compared to Zr alloys