The structure and speciation of fission products within the SiC barrier layer of tristructural-isotropic (TRISO) fuel particles irradiated to 19.6% fissions per initial metal atom (FIMA) burnup in the Advanced Test Reactor (ATR) at Idaho National Laboratory (INL) was investigated. As-irradiated fuel particles, as well as those subjected to simulated accident scenarios, were examined. The TRISO particles were characterized using synchrotron X-ray absorption fine-structure spectroscopy (XAFS) at the Materials Research Collaborative Access Team (MRCAT) beamline at the Advanced Photon Source. The TRISO particles were produced at Oak Ridge National Laboratory under the Advanced Gas Reactor Fuel Development and Qualification Program and sent to the ATR for irradiation. XAFS measurements on the palladium and silver K-edges were collected using the MRCAT undulator beamline. Analysis of the Pd edge indicated the formation of palladium silicides of the form Pd_xSi (2 ≤ x ≤ 3). In contrast, Ag was found to be metallic within the SiC shell safety tested to 1700 °C. To the best of our knowledge, this is the first result demonstrating metallic bonding of silver from fissioned samples. Knowledge of these reaction pathways will allow for better simulations of radionuclide transport in the various coating layers of TRISO fuels for next generation nuclear reactors. They may also suggest different ways to modify TRISO particles to improve their fuel performance and to mitigate potential fission product release under both normal operation and accident conditions.

在爱达荷州国家实验室（INL）的先进测试反应堆（ATR）中，三结构各向同性（TRISO）燃料颗粒的SiC阻挡层中，每个初始金属原子（FIMA）燃尽19.6％裂变的裂变产物的结构和形态为调查。检查了辐照过的燃料颗粒以及发生模拟事故情况的燃料颗粒。TRISO粒子在高级光子源处的材料研究合作访问团队（MRCAT）光束线中使用同步加速器X射线吸收精细结构光谱（XAFS）进行了表征。TRISO颗粒是在橡树岭国家实验室的高级气体反应堆燃料开发和鉴定计划下生产的，并被送至ATR进行辐照。使用MRCAT波荡器光束线收集了钯和银K边缘的XAFS测量值。对Pd边缘的分析表明形成了Pd形式的硅化钯_x Si（2≤x≤3）。相反，在经1700°C测试的SiC外壳安全性范围内，发现Ag是金属。据我们所知，这是证明裂变样品中银与金属的金属键合的第一个结果。对这些反应途径的了解将有助于更好地模拟用于下一代核反应堆的TRISO燃料的各种涂层中放射性核素的运输。他们还可能提出了不同的方法来改性TRISO颗粒，以改善其燃料性能并减轻正常运行和事故情况下潜在裂变产物的释放。