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NKS Programme Area:NKS-R
Research Area:Severe accidents
Report Number:NKS-438
Report Title:Main Outcomes of the TETRA Project on Tellurium Chemistry in a Severe Accident
Activity Acronym:TETRA
Authors:Fredrik Espegren, Teemu Kärkelä, Anna-Elina Pasi, Unto Tapper, Jon-Petter Omtvedt, Christian Ekberg,
Abstract:A joint study between VTT Technical Research Centre of Finland Ltd, Chalmers University of Technology, and the University of Oslo in the NKS-R TETRA activity (2019) was carried out to investigate the tellurium transport in the primary circuit system and the effect of the different spray solutions used in the containment spray system for the tellurium removal efficiency. Tellurium is considered to be one of the volatile fission products released in a severe nuclear power plant accident. The experimental work was carried using two different experimental setups at VTT. One setup utilized two furnaces; one used to volatilize (540 °C) the precursor (Te-metallic) and another one used as the reaction zone (1227 °C). This setup was used to observe the transport behavior of tellurium under the different investigated atmospheres (oxidizing and inert), both dry and humid. For the emergency spray solution investigation (water or two different alkaline borate solution), another setup with one furnace and spray chamber was used. The furnace was used to volatilize (840 °C and 540 °C) the two different precursors used (TeO2 and Te-metallic) and the volatilized species were transported to the spray chamber by the carrier gas establishing the experimental conditions (oxidizing and inert), both dry and humid. Both the transport experiments and the spray experiments also investigated the effect of CsI on Te behavior under humid conditions (oxidizing and inert). The transport experiments indicated the highest transport of the released Te through the experimental setup under oxidizing conditions compared to inert conditions. However, the highest release fraction of Te occurred under inert conditions. Increasing the humidity content of the atmosphere resulted in an increase in the fraction of tellurium transported under oxidizing and a decrease under inert conditions. The addition of CsI reduced the amount of tellurium transported to the filter and also the released amount of tellurium under oxidizing conditions. Moreover, CsI increased the tellurium fraction on the filter in humid inert conditions in comparison to the humid conditions without CsI. The containment spray system experiments showed that the tellurium bearing aerosols were generally efficiently removed under both oxidizing and inert conditions. Although, a decrease in the removal was observed when metallic Te precursor was used instead of TeO2. The airborne CsI increased the removal efficiency of tellurium. Furthermore, the addition of chemicals to the spray solution did have a noticeable effect when TeO2 was used as a precursor and less apparent when metallic Te was used.
Keywords:Tellurium, Cesium iodide, Containment spray system, Aerosol, Primary circuit, Severe Accident, Source Term
Publication date:04 Jun 2020
ISBN:ISBN 978-87-7893-529-8
Number of downloads:55
Download:pdf NKS-438.pdf

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