本研究旨在應用大氣傳送模式模擬輻射塵在大氣中的傳送行為與分布情形及對台灣之影響評估。吾人針對東亞國家核電廠進行2000年之氣流軌跡模擬，結果顯示中國廣東大亞灣核電廠與上海秦山核電廠氣流較易影響台灣，到達台灣機率為7 – 12%，到達台灣時間為46小時左右；韓國與日本南部之核電廠，氣流到達台灣之機率為10%，平均到達台灣之時間約為72小時。由季節頻率分布結果顯示中國南方核電廠與中國北方、韓國、日本等核電廠氣流影響台灣分別集中在春夏季與秋冬季，亞洲季風是主宰大氣擴散之主因。 透過模擬車諾比爾核電廠事故確立模式適用性之後，再經由模式參數敏感度測試，發現除了雲下清除係數無明顯變化之外，其餘參數設定會導致模擬結果有顯著性差異，尤以排放強度以及核種粒徑最為明顯。嚴重核事故情境之全年模擬顯示，中國核電廠輻射塵影響台灣機率為50 – 70%之間，台灣北部地區平均輻射沉降量約為103 Bq m-2以上，其輻射塵經過20 – 30小時即可到達台灣。 經由2001 – 2002年春季鋒面、梅雨鋒面以及東北季風等三個個案模擬中，發現沉降分布區域深受降水影響，大氣濃度分布位置則受垂直風場所主導，下沉氣流易使Cs-137輻射塵輸送至大氣邊界層內。當春季鋒面與梅雨鋒面經過台灣時，若中國大亞灣核電廠發生嚴重核事故，則台灣中部以北地區大約在第25小時左右將承受104 – 105 Bq m-2之Cs-137輻射塵沉降量；秦山核電廠輻射塵沉降至台灣的天氣型態為大陸冷高壓位於黃河河套，且事故當時無降水之際，估計最快到達台灣時間為1日之內，沉降區域涵蓋台灣60%之陸地。 本研究中存在幾點不確定性而使得模式無法適用於各種核事故之實際結果，即台灣鄰近國家核電廠資料、排放劑量以及濕沉降作用對於Cs-137影響程度，未來可加強在核事故發生之機制研究及增進模式對水汽的掌握。 This study is aimed to simulating the transport and dispersion of radioactive dust using an atmospheric transport model, and further to assess its impact on Taiwan. Based on 2001 ECMWF meteorological data, we characterized the forward trajectories of airflows originating from 10 nuclear power plant stations in East Asia, and also calculated the frequency of contaminated airflows arriving in Taiwan. The results showed that the airflow from the Qinshan power plant station in China has the highest frequency of 12% reaching Taiwan, and the average travel time is about 2 days. For the airflow from Korea and Japan, the frequency is about 10%, and travel time is within three days. The airflow arriving in Taiwan is strongly associated with Asian Monsoon. Using the Chernobyl accident initial conditions designed for our NCU-MM5-HYSPLIT model was testified with a good agreement with previous studies. A yearly simulation for the serious nuclear accident in Qinshan and Guangdong power plants was conducted. The results showed that Taiwan is located within a of 50 – 70%, the average Cs-137 deposition in northern Taiwan is about 103 Bq m-2 and travel time is within 20 – 30 hours. Case study showed that the rainfall can enhance Cs-137 deposition and the vertical motion can determine the maximum Cs-137 deposition locations. For the case of a frontal passage over northern Taiwan, 104 – 105 Bq m-2 was obtained within 25 hours. In contrast, when Qinshan nuclear power plant occurred severe accident in the case of northeast monsoon, radioactive dust can reach Taiwan within 1 day and cover the 60% of Taiwan land. Keyword: atmospheric transport model, trajectory analysis, radioactive dust.
