Leaching behavior of strontium in cementitious materials immobilizing boric acid enriched in B-10 isotope

Enriched boric acid with Boron-10 (¹⁰B-EBA) has recently emerged as an advanced neutron absorber for nuclear reactors, enabling enhanced control over fission processes, while natural boric acid (NBA) remains the traditional choice. The unique geochemical behavior of ¹⁰B-EBA, both in solution and solid phase, suggests the development of new cementitious waste forms for immobilizing radioactive waste streams containing ¹⁰B-EBA. This study examines how strontium (Sr) leaches from cementitious matrices containing NBA and ¹⁰B-EBA, focusing on the effect of boron enrichment on Sr leaching. Study specimens were prepared from Portland cement (PC), demineralized water, and solutions of either NBA or ¹⁰B-EBA. The leaching test on study specimens was conducted in accordance with ASTM C1308-08-2017, and Sr levels in leachates were measured by Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES). The mineralogical analysis of the solidified matrices was conducted using X-ray diffraction (XRD), and the mineral phase development was examined using scanning electron microscopy (SEM). Results showed that ¹⁰B-EBA-based specimens had lower Sr leachability than NBA-based specimens. The SEM images reveal that boron enrichment and leaching affect the development of mineral phases in hydration products. Leaching behavior models indicate that Sr release follows first-order reaction kinetics, diffusion, dissolution, or a combination of these processes. These findings are essential for improving the design and long-term stability of cementitious waste forms containing ¹⁰B-EBA.