高温气冷堆（High Temperature Gas-cooled Reactors，HTGRs）反应堆正常运行期间燃料元件中放射性核素的释放，对于维修剂量率有特别重要的影响，另一方面，正常运行期间一回路中累积的放射性核素可以成为假想事故的重要源项。因此源项计算的保守性对反应堆安全分析至关重要。 本课题使用STACY软件对高温气冷堆燃料元件中裂变产物的扩散和释放过程进行了详细的建模和离散化，并通过计算德国于利希研究中心热室的KÜFA设施中不同工况下燃料元件中的放射性源项，与实验测量结果进行对比，开展独立验证工作。研究源项评价过程和评价结果的保守性，这对于评价STACY程序模型可用于源项设计和校核计算具有重要意义。 研究表明，STACY程序不确定性的主要来源不是模型本身有缺陷，而是由强烈依赖的材料特性和具有很宽变化范围的输入数据引入的。使用STACY程序对于加热实验后进行计算的情况而言，计算结果都能够保守的覆盖实验数据，且绝大部分情况下，锶的释放被大大高估了。另一方面，UO2和基体材料的阻留能力是显而易见的，穿过碳化硅层的扩散输运机制是一种过于保守的假设。 金属裂变产物的释放远低于模型计算中得到的预期水平，即模型计算结果高估了释放值。铯和氪释放量对比研究表明辐射/加热中可能产生碳化硅层失效，但外热解碳层仍然完整。比较特殊的是，银的释放测量很不稳定，因此对于银的实验校算很难，这意味着用STACY评估高温堆中银的释放存在很大不确定性。 本研究的结论说明，STACY的计算结果具有一定保守性，特别是对于关键核素铯与锶核素的估计，该程序用于HTGR工程设计或校验是可行的。
The amounts of radionuclides in High Temperature Gas-cooled Reactors (HTGRs) under the normal operation condition are important for maintenance dose evaluating and the accumulated radionuclides in the primary loop under the normal operation condition are also essential for the evaluating the source terms of hypothetical accidents. Therefore, the conservative source terms calculation is crucial for the reactor safety analysis. The article analyzes the detail modeling and discretization of fission products diffusion in High Temperature Gas-cooled Reactors fuel elements with using STACY software, calculates the source terms under different conditions in of KÜFA fuel elements heating test done by Jülich, compares the test result and organizes the independent verification. To study the conservativeness of source terms evaluation process and result is of great importance in evaluating the adaptation of STACY software in source terms design and verification. The results show that the main uncertainties are most likely introduced less by shortcomings of the model, but rather by input data strongly depending on material properties and exhibiting a broader variability. It is obvious from postcalculations that the strontium data are largely overpredicted in most cases. While the retention capability of UO2 and the matrix material of the fuel spheres is visible, it is most probably the diffusive transport through the silicon carbide layer that appears very conservative and should undergo a thorough review. Metallic fission product release remained well below the expected levels from previous experience, which indicates release is largely overpredicted by the model calculations. The comparison of cesium and krypton release gives indication that during irradiation/heating particles with a failed SiC layer, but still intact oPyC layer may have developed. Silver release measurements are often unusual and inconsistent, and therefore extremely difficult for postcalculation. The results show that the STACY results are conservative, especially for the estimation of the important nuclides. The STACY program is feasible for engineering design and verification.
