Abstract Technetium-99 (99Tc) is an important radionuclide when considering the disposal of nuclear wastes owing to its long half-life and environmental mobility in the pertechnetate (Tc(VII)) redox state. Its behaviour in a range of potential cement encapsulants and backfill materials has been studied by analysing uptake onto pure cement phases and hardened cement pastes. Preferential, but limited, uptake of pertechnetate was observed on iron-free, calcium silicate hydrates (C–S–H) and aluminate ferrite monosulphate (AFm) phases with no significant adsorption onto ettringite or calcium aluminates. Diffusion of 99Tc through cured monolithic samples, representative of cements being considered for use in geological disposal facilities across Europe, revealed markedly diverse migration behaviour, primarily due to chemical interactions with the cement matrix rather than differential permeability or other physical factors. A backfill cement, developed specifically for the purpose of radionuclide retention, gave the poorest performance of all formulations studied in terms of both transport rates and overall technetium retention. Two of the matrices, pulverised fuel ash: ordinary Portland cement (PFA:OPC) and a low-pH blend incorporating fly ash, effectively retarded 99Tc migration via precipitation in narrow, reactive zones. These findings have important implications when choosing cementitious grouts and/or backfill for Tc-containing radioactive wastes.

中文翻译：

---

灌浆和回填水泥对锝 99 的保留：对放射性废物安全处置的影响

摘要 锝 99 (99Tc) 在高锝酸盐 (Tc(VII)) 氧化还原状态下具有较长的半衰期和环境流动性，因此在考虑处理核废料时是一种重要的放射性核素。通过分析纯水泥相和硬化水泥浆的吸收，研究了它在一系列潜在的水泥密封剂和回填材料中的行为。在无铁、硅酸钙水合物 (C-S-H) 和铝酸铁酸单硫酸盐 (AFm) 相上观察到优先但有限的高锝酸盐吸收，对钙矾石或铝酸钙没有显着吸附。99Tc 通过固化的整体样品扩散，代表被考虑用于整个欧洲地质处置设施的水泥，揭示了明显不同的迁移行为，主要是由于与水泥基体的化学相互作用，而不是不同的渗透率或其他物理因素。专为放射性核素截留而开发的回填水泥在所有研究配方中在传输速率和总体锝截留方面的性能最差。两种基质，粉状燃料灰：普通波特兰水泥 (PFA:OPC) 和掺有粉煤灰的低 pH 值混合物，通过在狭窄的反应区沉淀，有效地阻止了 99Tc 迁移。在为含钐放射性废物选择水泥浆和/或回填物时，这些发现具有重要意义。在传输速率和整体锝保留率方面，所有配方的性能最差。两种基质，粉状燃料灰：普通波特兰水泥 (PFA:OPC) 和掺有粉煤灰的低 pH 值混合物，通过在狭窄的反应区沉淀，有效地阻止了 99Tc 迁移。在为含钐放射性废物选择水泥浆和/或回填物时，这些发现具有重要意义。在传输速率和整体锝保留率方面，所有配方的性能最差。两种基质，粉状燃料灰：普通波特兰水泥 (PFA:OPC) 和掺有粉煤灰的低 pH 值混合物，通过在狭窄的反应区沉淀，有效地阻止了 99Tc 迁移。在为含钐放射性废物选择水泥浆和/或回填物时，这些发现具有重要意义。