放射性核素的局地尺度大气扩散研究对于开展核应急响应工作非常重要。Lagrange烟团扩散模型是一种在该尺度上快速准确地建立放射性辐射场的有力工具。该文开发了适用于局地尺度的Lagrange分裂烟团(SPUFF)扩散模型,其可适配加州气象(CALMET)模型。以CALMET模型驱动SPUFF扩散模型,开展局地尺度扩散模拟,假设以三门核电站作为扩散场景,基于风洞实验数据对SPUFF扩散模型进行性能验证,再基于福岛第一核电站附近的双葉町监测站已公布的监测数据进行模型的实用性评估。此外,针对烟团水平分裂阈值在上述场景开展了较全面的敏感性分析,以确定分裂开启条件。性能验证结果显示,SPUFF扩散模型性能优异,全部4个关键统计指标(模拟值在测量值2倍以内的比例、比例偏差、标准化均方误差和标准化绝对差)满足可接受模型标准。实用性评估结果显示,较Lagrange粒子模型LAPMOD,SPUFF扩散模型的模拟值可匹配更多的监测值;同时成功再现了反应堆事件引发的放射性核素释放导致的监测峰值效应。敏感性分析结果表明,单一气象条件(例如恒定风场)的复杂地形场景可采用不分裂模式;气象多变的复杂地形场景则有必要开启分裂模式。建议核电站局地尺度扩散的烟团水平分裂阈值为700~1 100 m。
Abstract
[Objective] Local-scale atmospheric dispersion modeling of radionuclides is crucial for nuclear emergency response during the early phase. The Lagrangian puff dispersion model excels in accurately and rapidly reproducing radioactive fields at this scale by accounting for natural turbulence and integrating wind fields with spatial and temporal variations. Given that nuclear power plants (NPPs), especially Chinese NPPs, are often located in heterogeneous terrains, which lead to channeling and slope flows, puff splitting in the puff dispersion model is necessary to accurately represent the phenomenon of plume splitting and layer decoupling phenomena. Despite its importance, the threshold values for puff splitting have not been adequately studied. In addition, the complex terrain around NPP sites generates highly complicated flows, necessitating the use of a diagnostic wind field model coupled with the atmospheric dispersion model to improve the accuracy of dispersion simulations. [Methods] To further provide an effective atmospheric dispersion modeling and establish threshold values of puff splitting for the Lagrangian puff dispersion model, the local-scale Lagrangian splitting puff dispersion model (SPUFF) was developed and fully integrated with the California meteorological model (CALMET). Two local-scale dispersion simulations were conducted using the CALMET to drive the SPUFF: one against the Sanmen NPP wind tunnel experiments with east (E) and northeast (NE) wind directions and another to simulate the Fukushima Daiichi nuclear accident. These simulations aimed to validate SPUFF's performance and practicality. Furthermore, a comprehensive sensitivity analysis was performed to determine the credible range of horizontal threshold values for puff splitting. The dispersion results were evaluated using multiple statistical metrics: the fraction of simulations within a factor of two/five/ten of the observations (FAC2/5/10), fractional mean bias (FB), normalized mean-square error (NMSE), normalized absolute difference (NAD), and geometric mean bias (MG). [Results] Validation results indicated that plumes generated by SPUFF effectively covered the majority of measurement sites, with coverage rates reaching 99.60% and 97.54% in the E and NE directions, respectively. All four crucial statistical metrics for SPUFF met acceptable criteria (FAC2: 0.52, FB: －0.17; NMSE: 0.75, NAD: 0.31 in the E direction; FAC2: 0.48, FB: 0.37; NMSE: 1.28, NAD: 0.39 in the NE direction), indicating remarkable performance. Practical evaluations demonstrated that SPUFF can reproduce more measurements in the Futaba station compared to the Lagrangian particle model (LAPMOD). SPUFF also successfully captured the concentration peak effects resulting from the reactor events during the Fukushima nuclear accident. Sensitivity analysis suggested that applying no puff splitting module might be sufficient for complex terrains with constant meteorological conditions (constant wind fields). However, puff splitting becomes crucial in complex terrains with variable meteorological conditions. For local-scale dispersion scenarios involving NPPs, the recommended threshold values for puff splitting range between 700 m and 1 100 m. [Conclusions] This paper provides a comprehensive evaluation of the Lagrangian splitting puff dispersion model (SPUFF) and demonstrates its practical application. The results strongly indicate that SPUFF is a valuable tool for future nuclear emergency responses. Additionally, this paper proposes a credible range of threshold values for puff splitting, offering guidelines for applying the puff model in local-scale dispersion scenarios at NPP sites.
关键词
Lagrange烟团扩散模型 /
风洞实验 /
福岛核事故 /
烟团分裂 /
敏感性分析
Key words
Lagrangian puff dispersion model /
wind tunnel experiments /
Fukushima nuclear accident /
puff splitting /
sensitivity analysis
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基金
国家自然科学基金青年基金项目(12105103);国家自然科学基金面上项目(12275152);北京市自然科学基金杰出青年基金项目(JQ23011);中国核工业集团有限公司领创研究项目
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