RuO4 interaction with surfaces in the containment of nuclear power plant

Licentiate thesis, 2014

During a severe accident different fission products will be released from the nuclear fuel and some of them may eventually reach the containment building. Ruthenium is considered to be an important fission product due to the possible formation of volatile oxides. Radiotoxicity and chemical toxicity of the volatile ruthenium compounds present a considerable hazard during the severe nuclear accident. In this work experiments regarding behavior of ruthenium tetroxide in the reactor containment were performed. Interaction of ruthenium tetroxide with zinc, copper, aluminium and epoxy paint in dry and humid atmosphere was examined. Several spectroscopic techniques were used to identify the chemical composition of the deposits formed after the interaction of RuO4 with different materials. Examination of the possible re-oxidation of ruthenium deposits to the volatile form by gamma radiation was also studied. Interaction of RuO4 with zinc, copper and aluminium had lead to different amounts of the deposited ruthenium among the metals. Most extensive deposition of RuO4 was observed on the aluminium metal. In dry atmosphere conditions preference of aluminium metal was very obvious. Deposits of ruthenium were identified to be a ruthenium dioxide on all metals. Speciation of the deposits formed on epoxy paint showed at least two different ruthenium species. One of them was identified to be probably a ruthenium dioxide, composition of the other one was not fully revealed. Experiments with the radiolytical re-vaporization of the ruthenium deposits from the epoxy paint indicated the release of ruthenium from the samples under the humid atmosphere. In the dry atmosphere re-vaporization of ruthenium wasn’t observed. The results showed how is ruthenium distributed between different materials in the containment. The chemical composition of the deposits was identified with use of different spectroscopic techniques. Dependence of re- vaporized ruthenium fraction on the received dose in the humid atmosphere was estimated.