Oxidation and Release of Ruthenium from Short Fuel Rods above 1500oC

The fission product ruthenium is radiotoxic and in oxidized form as ruthenium-tetroxide (RuO4) also chemical toxic. During fuel element change or in case of a leakage in fuel storages, air flows in the containment or fuel storage. If the circulation pump fails, the fuel elements are heated-up, and at high temperatures gaseous ruthenium oxides are formed and rapidly released from the fuel. Due to the significant higher volatility of RuO4 in the Chernobyl Catastrophe the measured concentration of the Ru-isotopes in the fall-outs was comparable to those of iodine and caesium. In order to get more insight in the chemical and physical behaviour of this fission product under severe accident conditions, the Ruthenium release was studied in a series of Separate Effect Tests (RUSET). In the test short fuel rod segments were used and exposed to air and steam atmosphere at high temperatures. The experiments in air atmosphere showed, that the partial pressures of the released Ru-oxides was two orders of magnitudes lower compared to those measured in previous tests with Ru-powder diluted in a ZrO2 matrix. It was found that ruthenium was not released in steam atmosphere in the examined temperature range. Furthermore, the temperature dependence of the deposition was detected by XRF analysis.JRC.F.4-Nuclear design safet

Cameras, Coyotes, and the Assumption of Equal Detectability

Remote cameras are an increasingly important tool in management and wildlife studies. However, we often do not know if they provide an unbiased sample of populations. Using a marked, radio-collared population of coyotes (Canis latrans) of known social status, we evaluated the influence of temporal (daily and seasonal) and spatial (distance between units, habitat, and proximity to human structures) factors on vulnerability to photo-captures. During 8 unbaited camera sessions of 6 weeks each, we obtained 158 coyote photographs at a photo-capture success rate of 1.6%. We were able to identify not only marked individuals, but also a number of uncollared adults through variation in their pelage. Photo-capture of adults peaked 2 weeks after we established camera stations. Annual success for photographing adult coyotes was greatest during March and April, which corresponded with the dispersal season. The majority of photo-captures occurred at night, and adult photo-captures peaked around midnight, with smaller peaks at dawn and dusk. Rather than reflecting a circadian activity pattern, nighttime captures seemed to reflect when adult coyotes were most vulnerable to photo-capture. Characteristics of camera locations, such as amount of human activity, being on roads versus trails, and habitat type, also influenced the number of photo-captures. We conclude that remote cameras do not always provide an unbiased sample of populations and that animal behavior is important to consider when using these systems. Researchers using camera techniques need to carefully consider when, where, and how cameras are placed to reduce this bias

Behavior of VVER Fuel Rods Tested Under Severe Accident Conditions in the CODEX Facility

The early phase of severe accidents in VVER reactors was simulated in the CODEX (COre Degradation EXperiment) facility with electrically heated fuel rod bundles. The selected test conditions and applied measurement techniques made possible the observation of some specific phenomena, such as the protective role of oxide scale during quenching of high-temperature bundles, the composition of gases produced during the oxidation of boron-carbide control rods, and the interlink between the aerosol release and the oxidation process. The general behavior of the VVER bundles did not differ significantly from that of the Western-design light water reactor bundles tested under similar high-temperature conditions, but the experiments emphasized that the application of VVER-specific material properties and models is essential for comprehensive numerical simulations.JRC.F.4-Nuclear design safet