Tellurium Behavior in the Containment Sump: Dissolution, Redox, and Radiolysis Effects

Abstract

In the event of a severe nuclear accident, one major concern is the release of radioactive material into the environment causing potential exposure of the general public to radiation. Among the volatile radionuclides are a range of tellurium isotopes. Due to the radioactivity and the volatility of tellurium, it has to be taken into account when assessing the overall effects of an accident. The interest in tellurium is not limited only to its release but also to the fact that some tellurium isotopes decay to iodine, and thus affect the iodine release behavior. The release and transport behavior of tellurium has been investigated over the past decades, however, the aqueous chemistry of tellurium in the complex containment sump system is still unclear. This study presents the behavior of tellurium dioxide in simplified containment sump conditions in relation to dissolution, redox reactions, and interactions with water radiolysis products. The results indicate that radiolysis products have a significant effect on tellurium chemistry in both a reducing and oxidizing manner depending on the solution composition. The redox reactions also affect the solubility of tellurium. The results show that the current information used to assess tellurium source term needs to be reevaluated for both severe accident management and for code validation purposes.

Formation Mechanism of Elemental Te Produced in Tellurite Glass Systems by Femtosecond Laser Irradiation

“…[ 58 ] However, the interaction with the species in an open‐air atmosphere in the plasma cannot be excluded completely. Therefore, the following reactions may have occurred while the plasma was present and facilitated Te formation in the open‐air atmosphere: [ 59 ] $$\[{\rm{Te}}{{\rm{O}}_3}\; = \;{\rm{TeO}}_3^{2 - } + 2{e^ - }\]$$ $$\[{\rm{TeO}}_3^{2 - } + 4{e^ - } + \;6{{\rm{H}}^ + }\; = \;{\rm{Te}}_{\left( {\rm{s}} \right)}^0\; + \;3{{\rm{H}}_2}{\rm{O}}\]$$ 3)In theory, this reaction can go as long as there is a source of Te in the focal volume, such as TeO 4 , TeO 3+1 , and TeO 3 units. Let us now examine the stopping mechanism of the t‐Te formation.…”

“…The X‐ray diffraction (XRD) pattern of the SAED pattern shows a slight shift from t‐Te (Te‐I), which corresponds to t‐Te (Te‐I) at 2 GPa. [ 59 ] Undefined weak diffractions point out a possible match with the Te‐II phase, [ 60 ] although further confirmation is needed with advanced characterization techniques. The electron‐lattice energy transfer in the fs‐laser process results in lattice heating in µs time scale with shock wave (pressure‐wave) generation.…”

“…[58] However, the interaction with the species in an open-air atmosphere in the plasma cannot be excluded completely. Therefore, the following reactions may have occurred while the plasma was present and facilitated Te formation in the open-air atmosphere: [59] TeO TeO 2…”

Radiolytic Degradation of Dimethyl Telluride in Aqueous Solutions

“…Until recent years, tellurium was expected to mostly be present in its elemental insoluble form, and to not cause additional concern in the sump (Beahm, 1987;Laurie et al, 2013). However, novel results have shown that tellurium in its inorganic form can oxidize to a more soluble form in the containment sump conditions by reaction with water radiolysis products (Pasi et al, 2020). The dissolved tellurium is consequently capable to take part in further reactions in the sump.…”