Forest fire propagation simulations for a risk assessment methodology development for a nuclear power plant

Yasushi Okano, Hidemasa Yamano
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引用次数: 9

Abstract

After the Fukushima Daiichi nuclear power plant [NPP] accident, there has been an increased concern with the safety of NPPs in terms of external hazards, one of which is a forest fire which can create potential challenges to safety functions and the structural integrity of an NPP. As a part of the development of a risk assessment methodology for forest fires as an external hazard, forest fire propagation simulations have been performed by using the FARSITE simulator. These simulations have been used to evaluate two intensity parameters (i.e. fireline intensity and reaction intensity) and three other key parameters (i.e. flame length, rate-of-spread, and forest fire arrival time) which are related to “heat” and “flame” effects on an NPP. Sensitivity analyses for a wide range of weather conditions were performed in order to identify the variable ranges of the intensity and other key parameters. The location studied was selected from among areas with typical topographical and vegetation surrounding NPPs in Japan. The NPP is facing the sea and surrounded by hills, distanced from an urban area, with mostly broad leaf forests, several paddy fields and a few pasture areas.

Low-to-high frequency weather conditions have been utilized in this analysis; forest fire propagation simulations were performed “with/without prevailing wind” (i.e. 0–24 m/s wind speed) and “high/low values for ambient temperature and relative humidity” (−4.3 to 37 °C and 5–99%, respectively) according to the recorded data ranges for the typical NPP site. The maximum values of fireline intensity and rate-of-spread are 4.7 × 102 kW/m and 2.4 m/min and they depend very much on prevailing wind speed and relative humidity (around 2.3 and 1.8 times respectively) but less on ambient temperature (around 1.1 times). Reaction intensity and flame length change within relatively narrow ranges (around 1.7 and 1.5 times respectively) even for all the variation in weather parameters. The forest fire arrival time at the site is reduced by a factor of 5 with changing prevailing wind speed from the recorded-highest to zero. The arrival time increases some 3.4 times with the highest humidity compared to the recorded-lowest conditions, although it is changed little even by varying ambient temperature.

Given that this study shows that the maximum height of a flame on a canopy top is close to the range of power line height, a loss of offsite power is recognized as a possible subsequent event during a forest fire.

森林火灾传播模拟,用于核电厂风险评估方法的开发
在福岛第一核电站事故之后,人们越来越关注核电站的外部危害,其中之一是森林火灾,这可能对核电站的安全功能和结构完整性造成潜在的挑战。作为开发森林火灾作为外部危害的风险评估方法的一部分,利用FARSITE模拟器进行了森林火灾传播模拟。这些模拟已用于评估两个强度参数(即火线强度和反应强度)和其他三个关键参数(即火焰长度、蔓延速度和森林火灾到达时间),这些参数与核电厂的“热”和“火焰”效应有关。对各种天气条件进行了敏感性分析,以确定强度和其他关键参数的变化范围。研究地点选自日本核电站周围具有典型地形和植被的地区。核电站面朝大海,四面环山,远离市区,主要有阔叶林、几片稻田和一些牧场。在本分析中使用了低至高频的天气条件;根据典型核电站站点记录的数据范围,进行了“有/无盛行风”(即0-24 m/s风速)和“环境温度和相对湿度的高/低值”(分别为- 4.3至37°C和5-99%)的森林火灾传播模拟。火线强度和蔓延速度的最大值分别为4.7 × 102 kW/m和2.4 m/min,它们主要取决于盛行风速和相对湿度(分别约为2.3和1.8倍),而对环境温度的影响较小(约为1.1倍)。反应强度和火焰长度的变化范围相对较窄(分别约为1.7和1.5倍),即使在所有天气参数的变化。随着盛行风速从最高记录变为零,森林火灾到达现场的时间减少了5倍。在湿度最高的情况下,到达时间比有记录的最低条件下增加了约3.4倍,尽管即使环境温度变化也几乎没有变化。鉴于本研究表明,冠层顶部火焰的最大高度接近电力线高度范围,因此在森林火灾期间,场外电力的损失被认为是可能的后续事件。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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