[en] The oxidation kinetics of various types of boron carbides (pellets, powder) were investigated in the temperature range between 800 and 1600degC. Mass spectrometric gas analysis was used to determine oxidation rates in transient and isothermal tests. The oxidation kinetics of boron carbide are determined by the formation of a liquid boron oxide layer and its loss due to the reaction with surplus steam to form volatile boric acids and/or direct evaporation at temperatures above 1500degC. The overall reaction kinetics are paralinear. Under the test conditions described in this report linear oxidation kinetics established soon after initiation of the oxidation. The oxidation kinetics are strongly influenced by the thermal-hydraulic boundary conditions, in particular by the steam flow rate. On the other hand, the properties of the B₄C sample itself have only a limited effect on the oxidation. Only very low amounts of methane were produced in these tests. The highest methane release was measured at the lowest test temperatures which is in agreement with thermo-chemical pre-test calculations. (author)

[en] The QUENCH bundle experiments together with pertinent separate-effects tests are run to investigate the hydrogen source term resulting from water injection into an uncovered core of a light water reactor for emergency cooling. The test bundle consists of 21 fuel rod simulators, 20 of which are heated electrically over a length of 1024 mm. The center rod is either an unheated fuel rod simulator or a control rod containing B₄C absorber material. The Zircaloy-4 rod cladding and the grid spacers are identical to those used in pressurized water reactors, whereas the fuel is represented by ZrO₂ pellets. After transient heating to 2000 K and above, cooling of the test bundle is accomplished by injecting water or steam into the bottom of the test section. Hydrogen generation during cooling was found either to stop almost immediately or to increase for a certain time. Increased hydrogen generation was found in those tests in which local melting occurred, probably as a result of oxidation of the melt containing zirconium. Hydrogen release in the flooding/cooling phase of all QUENCH experiments performed so far seems to be insensitive to the coolant (water or steam) under similar test conditions

[en] Various kinds of experiments on the oxidation of Zircaloy-4 cladding material in different scales and under different conditions at temperatures 800-1300 deg. C (small scale) and up to 2000 deg. C (large scale) are presented. The focus of this work was on prototypic mixed air-steam atmospheres and sequential reaction in steam and air, where no data were available before. The separate-effects tests were performed to support the large scale bundle test QUENCH-10 and to deliver first data for model development

[en] The Cr-Zr interaction of two types of Cr coated Zr alloy accident tolerant fuel (ATF) claddings, deposited by cold spraying and magnetron sputtering, was studied in argon in the temperature range from 1100 to 1300°C. A tube furnace with a sample lock system was used for fast exchanging samples at test temperature. Inter-diffusion between the coating and the substrate results in the formation of an intermetallic ZrCr₂ layer and a solid solution layer beneath. Some pores were formed on the interlayer by a Kirkendall-type mechanism. The interlayer growth rate of cold sprayed samples was always slightly higher than that of magnetron sputtered samples in the same condition. Moreover, the temperature-dependent consumption coefficient of the Cr coating was calculated and fitted to an Arrhenius function. The dissolution and precipitation behavior of Cr in the Zr substrate and the diffusion behavior of Zr in Cr coating were also studied.

[en] Highlights: • Surface Cr coating improved the oxidation resistance of the substrate up to 1500 ℃. • The thickness of Cr₂O₃ scale significantly decreased at 1300–1400 °C. • Cr in coating diffused to the center of substrate with the oxidation of substrate. • The ZrCr eutectic reaction significantly affected the coating microstructure. • The transformation of t-ZrO_2−x to c-ZrO_2−y occurred in substrate at ~1500 °C. The transient oxidation behavior of magnetron-sputtered chromium-coated Zircaloy-4 was studied in steam up to 1600 °C, and the microstructural evolution of the coating-substrate system after oxidation was investigated. Coating failure and corresponding rapid oxidation of coating and substrate occurred at 1300–1400 °C. It was mainly caused by the thickness decrease of the outer dense Cr₂O₃ scale, the ZrCr eutectic reaction, the ZrCr interdiffusion, and the precipitation of ZrO₂ along unoxidized Cr grain boundaries. The phase transformation of tetragonal ZrO_2−x to cubic ZrO_2−y increased the oxidation rate of the Zircaloy-4 substrate at ~1500 °C through the higher oxygen diffusion coefficient in the cubic phase.