Uncertainty analyses of fission product yields are indispensable in evaluating reactor burnup and decay heat calculation credibility. Compared with neutron cross section, there are fewer uncertainty analyses conducted and it has been a controversial topic by lack of properly estimated covariance matrix as well as adequate sampling method. Specifically, the conventional normal-based sampling method in sampling large uncertainty independent fission yields could inevitably generate nonphysical negative samples. Cutting off these samples would introduce bias into uncertainty results. Here, we evaluate thermal neutron-induced U-235 independent fission yields covariance matrix by the Bayesian updating method, and then we use lognormal-based sampling method to overcome the negative fission yields samples issue. Fission yields uncertainty contribution to effective multiplication factor and several fission products’ atomic densities at equilibrium core of pebble-bed HTGR are quantified and investigated. The results show that the lognormal-based sampling method could prevent generating negative yields samples and maintain the skewness of fission yields distribution. Compared with the zero cut-off normal-based sampling method, the lognormal-based sampling method evaluates the uncertainty of effective multiplication factor and atomic densities are larger. This implies that zero cut-off effect in the normal-based sampling method would underestimate the fission yields uncertainty contribution. Therefore, adopting the lognormal-based sampling method is crucial for providing reliable uncertainty analysis results in fission product yields uncertainty analysis.

中文翻译：

---

基于对数正态的裂变产物采样在卵石床HTGR中产生不确定性传播

裂变产物收率的不确定性分析是评估反应堆燃耗和衰减热计算可信度必不可少的。与中子截面相比，进行的不确定性分析较少，并且由于缺乏适当估计的协方差矩阵以及适当的采样方法而引起争议。具体而言，常规的基于法线的采样方法在对不确定性大的裂变产量进行采样时，不可避免地会生成非物理的负采样。截取这些样本将在不确定性结果中引入偏差。在这里，我们通过贝叶斯更新方法评估热中子引起的U-235独立裂变产率协方差矩阵，然后使用基于对数正态的采样方法来克服负裂变产率样本问题。裂变产生了对有效倍增因子的不确定性贡献，并对卵石床HTGR平衡核处的几种裂变产物的原子密度进行了定量和研究。结果表明，基于对数正态的采样方法可以防止产生负屈服样本，并保持裂变屈服分布的偏度。与基于零截止法线的抽样方法相比，基于对数法线的抽样方法评估了有效乘数的不确定性，并且原子密度更大。这意味着基于法线的采样方法中的零截止效应将低估裂变产量的不确定性贡献。因此，采用基于对数正态的抽样方法对于在裂变产物产量不确定性分析中提供可靠的不确定性分析结果至关重要。