報告書番号

N09031

タイトル（和文）

降下火山灰の体系的リスク評価に向けて－留意点と課題－

タイトル（英文）

Considerations on comprehensive risk assessment and mitigation planning of volcanic ash-fall.

概要 （図表や脚注は「報告書全文」に掲載しております）

降下火山灰の特徴，影響事例と対策に関し，火山学・工学・防災科学・社会学の各分野にまたがる文献調査を行い，降下火山灰の影響に対し体系的評価を行い，対策を立案する上での留意点と，定量的予測手法を開発するための課題を明らかにした．影響評価では，細粒粒子が風で再移動することや，火山泥流の発生により，影響の及ぶ地域の拡大，期間の長期化に留意する．また，水に飽和した火山灰は比重が大きいうえに，湿った火山灰は碍子に付着しやすく，導電性を有するため，碍子の絶縁特性が低下し，せん絡が発生することに留意する． 外部機関との連携，影響評価と対策の実施を促進するために，降灰除去作業に関するリスクコミュニケーション技術を開発する必要がある．降下火山灰の定量的予測は，工学的影響評価の基礎情報を与える．降下火山灰を精度よく予測するためには，噴煙高度に影響を与える大気条件を定量的に明らかにする必要がある．

概要 （英文）

Volcanic ash-fall is inevitable hazard throughout Japan, and causes wide range of effects due to its physical and chemical properties. Nuclear power plants in Japan face the necessity to assess the risk from volcanic ash-fall. Risk assessment of the volcanic ash-fall should include engineering solution and mitigation planning as well as the ash-fall hazard.
This report points out the characteristics for reducing the various effects of volcanic ash-fall as follows. Large-scale eruptions produce prominent volcanic ash-falls that can approach power plants at a great distance. Aftermath hazards of ash-fall events, such as remobilization of fine ash particles and generation of lahars, require further assessments. The kind and extent of damages becomes greater whenever ash is wet. Wet ash requires separate assessments in contrast to dry ash.
The mitigation and recovery measures at power plants involve quick cleanup operations of volcanic ash. Those operations should be prepared through comprehensive risk assessment, and by cooperation with authorities, during pre-eruption repose period. The comprehensive assessment for volcanic ash-fall hazards, however, has yet to be conducted. Development of risk communication method may result in increased implementation mitigation planning.
Numerical analysis of the ash-fall hazards provides quantitative data on particle motions that can be used in the risk assessment. In order to implement the quantitative assessment method, the verification on the effect of ambient air condition to the altitude of volcanic ash cloud is necessary. We need to develop a three-dimensional model of volcanic ash cloud, and calculate motions of ash clouds under multiple conditions of ambient air.

報告者

キーワード