Mobilization and Management of Tellurium in Severe Accident Scenarios

Doctoral thesis, 2022

Safety is one of the highest priorities in any industry. In the nuclear industry, safety is in the essence since in case of a nuclear accident, the consequences can be long-lasting, hazardous, and devastating to the public, environment, and the industry. Although only two accidents of highest significance have occurred, their influence is still present today. One of the most severe consequences of a severe nuclear reactor accident is the release of radioactive material to the environment. Different characteristics, such as volatility, toxicity, and half-life, of the released elements determine their effect and significance. Among the released radionuclides is tellurium. The tellurium isotopes released in the major accidents are highly volatile and have half-lives long enough to make tellurium important especially in the early stages of an accident. The released tellurium isotopes can cause increased radiation dose to the public during the first weeks after the accident. Moreover, many of the tellurium isotopes released decay to iodine isotopes which is also a concern due to the increased risk of thyroid cancer iodine can cause.

The aim of this work was to investigate phenomena involving tellurium occurring inside the containment building during a severe nuclear accident. The work is divided into mobilization of tellurium species and their management. The results obtained in this research provide valuable information on the behavior of tellurium in severe accident scenarios. The reactions leading to increased solubility and volatility were shown. High emphasis was put on the formation, stability, and mitigation of organic tellurides. The formation of a variety of organic tellurides from paint solvents under gamma irradiation was observed. This causes concerns about possible re-volatilization leading to post-accident releases. In addition to the increased mobility, this work provides information on the mitigation of tellurium species in accident scenarios. The containment spray system was found to be relatively effective in removing tellurium species from the containment atmosphere. In addition, activated charcoal materials trapped dimethyl telluride well. However, some reversibility was observed which raises interest on the adsorption mechanism. The results presented in this work lay the foundation for further studies on tellurium behavior in the containment. The evidence showing the formation of organic tellurides is especially significant since that could potentially lead to increased releases.