Tellurium interaction with surfaces in the containment and sea-salt residue

Licentiate thesis, 2018

In the event of a nuclear accident, the release of radionuclides is always a concern. The extent of such releases is affected by several factors, for example type of atmosphere, temperature, and what structural materials are present during the accident. The release of tellurium is especially worrying due its volatility, reactivity, and decay product of iodine. Moreover, the radiological and chemical toxicity of tellurium will during an accident be considerably problematic, to the public and nature. This work is divided into two experimental parts in order to determine: (1) the interaction between tellurium and metallic structural material found in the containment and (2) investigate the potential effect when using seawater as a coolant focusing on sea-salt residue. All experiments were performed at the relevant temperature (depending on the which part) under oxidizing and inert conditions and for the containment experiments humidity was also investigated. The structural material investigated were the metal surfaces aluminum, zinc, and copper with the aim of determining morphology, chemical speciation and if a reaction occurred between the metal surface and tellurium. For the investigation of seawater, determining if a chemical reaction(s) between tellurium and sodium chloride occurs and at what temperature. Results from the containment experiments using a furnace showed signs of possible reaction between tellurium and the copper surface under inert humid conditions close to room temperature. Otherwise, tellurium deposition occurred on the metal surfaces with no observable chemical reaction and no strong attachment to the surface. The deposit formed on the surfaces and the observed chemical species under the different conditions, determined using different spectroscopy methods, were as follows: TeO2 under oxidizing with (crystal structure paratellurite) and without humidity (crystal structures: paratellurite and orthorhombic), Te-metallic under inert conditions both with and without humidity, and finally Cu7Te4 was seen in the deposits on the copper surface under humid inert conditions. For the seawater investigation, two methods where used thermogravimetric analysis and furnace experiments. The results from these methods showed that under inert conditions, no indication of interaction was seen. However, for oxidizing conditions an interaction for all samples was observed that prevented an otherwise seen mass increase of the tellurium reference. Through the furnace experiments, the appearance of the samples at increasing temperatures were studied and used to support the thermogravimetric analysis.