Results of AgInCd absorber rod experiment QUENCH-13

The QUENCH experiments are to investigate the hydrogen source term resulting from the water injection into an uncovered core of a Light-Water Reactor (LWR) as well as the high-temperature behavior of core materials under transient conditions. The typical QUENCH test bundle consists of 21 fuel rod simulators with a total length of approximately 2.5 m and a heated length of 1 m. In the QUENCH-13 test, the single unheated fuel rod simulator in the center of the fuel bundle was replaced by a PWR control rod. The QUENCH-13 experiment investigated the effect of this control rod on early-phase bundle degradation, i.e. AglnCd/stainless steel/Zircaloy-4 control rod materials on oxidation and melt formation, and on reflood behavior. Furthermore, in the frame of the EU 6 th Framework network of excellence SARNET, release and transport of aerosols of a failed absorber rod were to be studied in QUENCH-13 which was conducted as a variant to QUENCH-06. The test comprised preoxidation, transient, and quench water injection at the bottom of the test section. The QUENCH-13 test was performed at the Forschungszentrum Karlsruhe on 7 November, 2007. It was supported by PSI (Switzerland) and AEKI (Hungary) regarding aerosol measurements and by PSI, GRS (Germany) and EdF (France) regarding calculational support. It had been preceded by a low-temperature (maximum about 1100 K) pre-test on 27 September, 2007 that characterized the bundle behavior and tested the aerosol measurement equipment. The determination of the test protocol was based on numerous calculations with various SFD computer codes. The final pre-test calculations were performed by PSI using the SCDAP-based codes. In the main test control rod failure was monitored at about 1415 K by temperature response of the absorber rod cladding and additionally by the PSI on-line aerosol analyzer. Significant release of aerosols was observed at ∼1450 K, and absorber melt relocation started at ∼ 1500 K. EDX analyses of aerosols collected after control rod failure show significant content of Cd and In (both -33 wt%) with minor parts of O, W (from the electric heaters), Ag and Fe. At initiation of reflood, no temperature escalation occurred which corresponds to the small amount of about 1 g in hydrogen production during the quench phase (compared to 42 g of H 2 during the pre-reflood phases). A significant part of the hydrogen produced by steam oxidation was absorbed. The hydrogen concentration in the remaining metal does not increase monotonically with increasing temperature. Hydrogen is enriched at positions where the breakaway effect occurs. Posttest bundle structures do not show much melt except AglnCd melt droplets at some elevations, particularly in the annulus of absorber rod cladding and guide tube and in the coolant channels surrounding the control rod, at elevations between the third (0.59 m) and first spacer grids (-0.06 m). Zr in the melt stems solely from the guide tube and not from the rod claddings due to a limited maximum bundle temperature of ∼1800 K. QUENCH-13 allowed studying the initiation of absorber rod failure by eutectic reactions of SS-Zr, and later on of AglnCd-Zr, as well as the redistribution of the absorber material within the test bundle. Furthermore, input data for modeling of aerosol release during severe accidents are considered as benefits of the experiment.