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<p>The migration behavior of radioactive selenium-79 (Se-79), a key long-lived fission product, through the various barrier systems critically influences the long-term safety and environmental risk of high-level radioactive waste (HLW) repositories. This study systematically reviews recent advances in Se-79 migration mechanisms and multi-field coupled numerical simulations, offering new insights and theoretical support for safety assessments. Research has revealed that multi-field coupling—encompassing thermal, hydraulic, mechanical, chemical, and biological (THMCB) processes—exerts synergistic control on Se-79 migration. Temperature gradients enhance solute migration via thermally induced convection; complex water–rock interactions regulate selenium redox transitions [e.g., Se(VI)/Se(IV)], thereby influencing its solubility and adsorption; stress field variations modify fracture–matrix structures and affect nuclide retention; and microbial activity promotes biopassivation through reduction reactions that immobilize soluble selenium species into insoluble forms. To quantify these coupled processes, this paper compares and evaluates the applicability and limitations of widely used reactive transport modeling tools, including PHREEQC, TOUGHREACT, PFLOTRAN, OpenGeoSys, COMSOL Multiphysics, and GoldSim. These models have demonstrated promising potential in scenario analyses for pre-selected sites, such as the Beishan area in China. Despite notable progress, challenges remain in developing dynamic valence-resolved geochemical models, achieving multiscale characterization of fracture–matrix interactions, and implementing fully integrated THMCB simulations. Future research should focus on integrating advanced in situ experimental techniques (e.g., high-temperature tracer tests at the Beishan Underground Laboratory), AI-assisted parameter optimization, and next-generation high-performance computing to construct intelligent, predictive multi-field coupled models. Such efforts will enhance the accuracy and reliability of long-term Se-79 migration predictions and strengthen the scientific foundation for the safety assessment of HLW geological disposal systems, contributing to global carbon reduction and sustainability goals.</p>

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Multi-field coupled simulation of radioactive selenium-79 migration in geological disposal systems of high-level radioactive wastes: advances and innovative insights

  • 期刊论文

  • 发表日期：

    2026年2月14日

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  • Xianzhe Duan,
  • Bingqing Shao,
  • Nan Li,
  • Kaituo Shi,
  • Wenzhou Xiao,
  • Jiale Dou,
  • Jiawei Wang,
  • Huan Huang,
  • Liping Shu,
  • Hafiza Tasneem Nazish

摘要

The migration behavior of radioactive selenium-79 (Se-79), a key long-lived fission product, through the various barrier systems critically influences the long-term safety and environmental risk of high-level radioactive waste (HLW) repositories. This study systematically reviews recent advances in Se-79 migration mechanisms and multi-field coupled numerical simulations, offering new insights and theoretical support for safety assessments. Research has revealed that multi-field coupling—encompassing thermal, hydraulic, mechanical, chemical, and biological (THMCB) processes—exerts synergistic control on Se-79 migration. Temperature gradients enhance solute migration via thermally induced convection; complex water–rock interactions regulate selenium redox transitions [e.g., Se(VI)/Se(IV)], thereby influencing its solubility and adsorption; stress field variations modify fracture–matrix structures and affect nuclide retention; and microbial activity promotes biopassivation through reduction reactions that immobilize soluble selenium species into insoluble forms. To quantify these coupled processes, this paper compares and evaluates the applicability and limitations of widely used reactive transport modeling tools, including PHREEQC, TOUGHREACT, PFLOTRAN, OpenGeoSys, COMSOL Multiphysics, and GoldSim. These models have demonstrated promising potential in scenario analyses for pre-selected sites, such as the Beishan area in China. Despite notable progress, challenges remain in developing dynamic valence-resolved geochemical models, achieving multiscale characterization of fracture–matrix interactions, and implementing fully integrated THMCB simulations. Future research should focus on integrating advanced in situ experimental techniques (e.g., high-temperature tracer tests at the Beishan Underground Laboratory), AI-assisted parameter optimization, and next-generation high-performance computing to construct intelligent, predictive multi-field coupled models. Such efforts will enhance the accuracy and reliability of long-term Se-79 migration predictions and strengthen the scientific foundation for the safety assessment of HLW geological disposal systems, contributing to global carbon reduction and sustainability goals.