The evolution of hydrated lime-based cementitious waste forms during leach testing leading to enhanced technetium retention

Design and Application of Materials for Sequestration and Immobilization of 99Tc

“…145 CWF is an alternative to glass waste forms with lower processing temperatures and could be more suitable for immobilization of 99 Tc. 146,147 Currently, CWFs are comprehensively used for the immobilization of various LAW/LLW globally. 148−150 Cast Stone, a low temperature CWF, has been efficiently investigated for the immobilization of various radionuclides including 99 Tc present in LAW at Hanford Site, USA.…”

“…However, the high processing temperatures (>1000 °C) warrant the exploration of low-temperature waste forms that do not destabilize 99 Tc and other radionuclides . CWF is an alternative to glass waste forms with lower processing temperatures and could be more suitable for immobilization of 99 Tc. , Currently, CWFs are comprehensively used for the immobilization of various LAW/LLW globally. − …”

Follow-on Report of Analysis of Approaches to Supplemental Treatment of Low–Activity Waste at the Hanford Nuclear Reservation (Volumes I & II)

“…Many anions will remain in the pore solution in the waste form, and the release would be controlled by the physical transport pathways in the waste form (e.g., NO3 -, NO2 -, I -, Tc(VII)O4 -). However, recent works have shown that some of these contaminants (Tc and I) can incorporate into the matrix phases, providing improved retention (Bourchy et al, 2022;Gillispie et al, 2020;Guo et al, 2020;; VSL-21R5000-1, Development of Improved Grout Waste Forms for Supplemental Low Activity Waste Immobilization).…”

“…However, work at the 222-S Laboratory recommended the use of a formulation containing hydrated lime, BFS, and OPC to react the excess sulfate (RPP-RPT-31077, Effluent Treatment Facility Waste Stream Monolith Testing Phase II). Testing of this formulation at Pacific Northwest National Laboratory (PNNL) and SRNL demonstrated acceptable performance, including enhanced technetium retention (PNNL-25129, Liquid Secondary Waste Grout Formulation and Waste Form Qualification; SRNL-STI-2015-00685, Liquid Secondary Waste: Waste Form Formulation and Qualification; Bourchy et al, 2022). This effort to address the sulfate content was a successful demonstration of adapting a grout formulation to address changes in waste composition.…”

“…PNNL has investigated getters as an additive to Cast Stone and also as amendments for backfill in the IDF at Hanford (Asmussen, et al, 2015;Asmussen, et al, 2017;Boglaienko et al, 2019;Burgeson et al, 2011;Pearce et al, 2018;Saslow et al, 2017). Most of the technetium getters tested to date have focused on using reduction-oxidation control to suppress technetium migration; however, ion exchange and incorporation processes have also been studied (PNNL-19681, Tc-99 Ion Exchange Resin Testing;Saslow et al, 2018;Bourchy et al, 2022). Additional work is in progress to expand and optimize the performance of technetium getter materials.…”