Synopsis and outcome of the QUENCH experimental program

Influence of oxide layer morphology on hydrogen concentration in tin and niobium containing zirconium alloys after high temperature steam oxidation

Study of boron behaviour in the primary circuit of water reactors under severe accident conditions: A comparison of Phebus FPT3 results with other recent integral and separate-effects data

Investigation on boron carbide oxidation for nuclear reactor safety: Experiments in highly oxidising conditions

Silicon Carbide‐ and Boron Carbide‐Based Hard Materials

Boron carbide is widely used as neutron absorbing control rod material in Western Boiling Water Reactors (BWR) and Russian RBMKs and WERs and some Pressurised Water Reactors (PWR). During a hypothetical severe accident the B 4 C reacts with the surrounding stainless steel cladding forming eutectic melts at temperatures above 1200 °C which is far below the melting temperatures of all components. The remaining uncovered absorber material as well as the B 4 C/metal mixtures may be exposed to the steam in the reactor core. The oxidation of boron carbide is highly exothermic and produces various gaseous reaction products like H 2 , CO, CO 2 and CH 4 which may affect the fission product chemistry. Extensive test series were performed to study the oxidation behaviour of boron carbide at high temperatures. Four types of B 4 C specimens with quite different properties were investigated under various atmospheres in the temperature range between 800 and 1600 °C. In contrast to most of the data published so far mainly at lower temperatures which are based on the evaluation of mass changes, gas production data were used to determine the oxidation kinetics of B 4 C in steam. The oxidation kinetics of boron carbide are determined by the formation of a liquid boron oxide barrier diffusion layer and its loss due to the reaction with surplus steam to form volatile boric acids andlor direct evaporation at temperatures above 1500 °C. The overall reaction kinetics are paralinear. Under the conditions typical for severe accidents (high temperatures and steam flow rates) linear oxidation kinetics establishes soon after initiation of the oxidation. The oxidation kinetics are strongly influenced by the surrounding conditions, in particular by the steam flow rate and the steam partial pressure. On the other hand, the properties of the B 4 C sample itself have only a limited effect on the oxidation. Only very low amounts of methane - which is of interest for the fission gas chemistry due to the formation of organic iodine - were produced in these tests. The highest methane release was measured at the lowest test temperatures in agreement with thermo-chemical pre-test calculations. This report updates and replaces the internal report SAM-COLOSS-P026 published as one deliverable of the EC COLOSS program (5 t h Framework Program 2000-2003).

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Experiments on the oxidation of boron carbide at high temperatures

First results of the QUENCH-13 bundle experiment with a silver-indium-cadmium control rod.

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). The QUENCH test bundle consists of 21 fuel rod simulators with atotal length of approximately 2.5 m. The QUENCH-08 test (without B 4 C absorber), performed at the Karlsruhe Research Center on July 24, 2003, was set up as a reference test to be compared to the QUENCH-07 experiment (with B 4 C absorber). So, the major objective of the test was to investigate the impact of B 4 C absorber on oxidation and H 2 generation, respectively, and bundle degradation. The test phases of both experiments were similar, as there were heatup, preoxidation (a quasi-stationary phase at -1700-1760 K for -15-16 min), transient, and cooldown by steam with a flow rate of 15 g/s. Temperatures during the transient and cooldown phases of QUENCH-08, however, were somewhat lower than during those phases of QUENCH-07. All the observations within the heated zone indicated immediate cooling upon steam injection. Several locations toward the top of and above the heated zone, however, experienced a strong escalation with maximum temperatures of -2100 K at the 950 mm level at the beginning of cooling and -2300 K at the 1150 mm level during the cooling phase. Associated with this escalation an increased release of hydrogen was observed during the cooling phase for a period of about 2 minutes. The evaluation of the QUENCH-08 mass spectrometer data resulted in -84 g of hydrogen release in total compared to -180 g during test QUENCH-07. According to the posttest examination, the bundle damage progression was initially dominated by rod cladding conversion due to steam oxidation and pellet contact. The distribution of some released molten cladding residues was unimportant, but relocation took place due to shroud melting, penetration of additional melt into the bundle, and candling. Overheating of upper elevations in the transient, continuing during the steam cooling phase, gave rise to massive cladding melt formation and relocation.

L. Steinbock

Papers

Experiments on the oxidation of boron carbide at high temperatures

First results of the QUENCH-13 bundle experiment with a silver-indium-cadmium control rod.

Experimental and computational results of the QUENCH-08 experiment. (Reference to QUENCH-07)