The QUENCH experiments series is focused on the determination of the hydrogen source term resulting from the water or steam injection into an uncovered core of a light water reactor (LWR). Closely connected aims are to study the scenario strongly dependent on core damage progression and the insufficiently understood mechanisms related to re-flooding and core recovery, as well as to provide information for an advanced treatment of the phenomena in codes. The experimental program relies on out-of-pile simulation of core conditions in parametric manner by use of electrically heated fuel rod simulator bundles. Essential information can be obtained, but transcription to fully realistic core conditions is seen as separate verification task requiring support from in-pile experiments and code analysis. The QUENCH test bundles consist of a central rod and 20 surrounding fuel rod simulators heated over a length of 1024 mm. The Zircaloy-4 (Zry) fuel rod claddings and the grid spacers are identical to those used in pressurized water reactors, whereas the fuel is represented by ZrO 2 pellets. The test section is instrumented with thermocouples (TC) attached to the rod cladding, the shroud, and the double-walled cooling jacket at levels between -50 mm and 1350 mm. Centerline TCs are mounted inside three of the four corner rods. The experiments are performed in flowing superheated steam / argon carrier gas atmosphere. The off-gas is mainly analyzed by a mass spectrometer. QUENCH-09, performed at Karlsruhe Research Center on 03 July, 2002, was the second experiment after QUENCH-07 with a control rod arrangement in the bundle center, consisting of absorber rod (B 4 C pellets / stainless steel cladding) and Zry guide tube. The steel to B 4 C mass ratio of 3.5 was identical to that in the future PHEBUS FPT3 experiment. In addition to the usual TC instrumentation three TCs were embedded in a groove of the absorber rod cladding. QUENCH-09 was conducted similarly to QUENCH-07, except for two items: First, the steam flow was reduced from 3.4 to 0.4 g/s during the "B 4 C oxidation phase" to reach steam starvation in the bundle and thus to provide closer comparison with the PHEBUS FPT3 experiment. Second, cooling was achieved with 50 g/s of saturated steam (instead of 15 g/s in QUENCH-07) in order to cool down the bundle as fast as possible to preserve its state before cooling initiation. Both tests are to investigate the control rod failure and the effect on the degradation of the surrounding fuel rod bundle. With respect to volatile fission products chemistry the gaseous species from B 4 C oxidation and control rod degradation were determined. The experiments were co-sponsored by the European Community within the "COLOSS" project. Control rod leakage was deduced from filling gas signal detection in the off-gas pipe at ∼1555 K, roughly the same absorber rod temperature as in QUENCH-07 (-1585 K). In spite of this, mass spectrometry has determined then and until the cooling phase only unexpectedly faint signals of volatile control rod degradation products compared to QUENCH-07. In the cooling phase the violent H 2 release was accompanied by large increases in the generation of CO and CO 2 . Further, boric acid generation was identified as well as a small amount of methane formation detected. Mass spectrometer data evaluation on basis of the combined amounts of CO and CO 2 as well as metallographic post-test examinations of the bundle resulted in a calculated oxidative conversion of roughly 50 % of the available B 4 C mass (compared to roughly 20 % in QUENCH-07). The nominal contribution of B 4 C oxidation to the H 2 signal, i.e. 2.2 % is comparable to 2.4 %, the respective percentage determined for QUENCH-07, but those figures do not indicate the secondary influences on the degradation of both bundles.