由日本福島事件之啟示，省思核能安全之強化

2011年3月11日，日本本州東北宮城縣外海發生震矩規模9.0之超級大地震，伴隨大海嘯侵襲沿岸地區。除造成日本東北地區工商業重大破壞及人員傷亡外，亦導致核能電廠之緊急狀態，福島第一核能發電廠中三座機組，均因缺乏冷卻能力而疑似發生爐心熔毀，亦因失去包封圍阻功能，導致大量放射性物質外釋。事件發生後數個月，核電機組尚未完全穩定，20公里內居民亦仍強制撤離安置中。核能安全是核能和平使用的基石。311福島事件衝擊核能安全的架構，未來詳細的檢討與徹底改善將無可避免。核能電廠最重要的三項安全設計目標中，於地震發生時核能機組均能達成安全停機之設計目標，此時緊急冷卻系統亦依據設計程序啟動。但隨後而來，遠超過設計基準的大海嘯，淹沒了岸邊的海水泵、席捲了電廠近海岸區域之油槽等露天設備，亦造成包括緊急柴油發電機在內之部分廠房淹水，由於先前的地震與海嘯已造成外電喪失，從此福島第一核電廠各機組均進入喪失交流電源之全黑狀態。由於未能在直流電池供應的短時間內恢復交流電力及供應充足水源，終於造成爐心冷卻能力喪失，爐心中燃料裸露而熔損。隨後因一次圍阻體洩壓與氫爆，導致兩層圍阻體均喪失包封功能，並導致大量放射性物質外釋，造成民眾恐慌之全球矚目事件。本文將就日本福島第一核電廠之設計概況及311事件始末，探討其安全設計目標面臨之挑戰，進而從整體事件之演變與啟示，提出核電廠安全設計準則強化之省思與建議。

關鍵字

核能安全；共因失效；電廠全黑；福島核災事件；地震與海嘯

並列摘要

Significant damage occurred to Tohoku area, northern-east of Honshu island in Japan, following a magnitude 9.0 earthquake and subsequent tsunami on 11 March 2011. The earthquake and tsunami were also caused emergencies of nuclear power plants. Three units of Fukushima Daiichi nuclear power station suffered core melt after their cooling system failed and then released massive radioactive isotope due to malfunction of confinement after hydrogen explosion occurred at reactor building. Those reactors are still unstable and people living within 20 Km are forced to evacuate over several months after the event.Safe shutdown, coolability and confinement are three major design bases for nuclear power system. At the time of the earthquake struck the nuclear power plant, the reactor cores were shutdown automatically as soon as the detected vibration higher than their shutdown set point. The emergency core cooling systems started up successfully following the emergency procedure. Unfortunately, the offsite power were lost due to big earthquake and the plant emergency power supply system, including diesel generator and dc power, were severe damaged and flooded due to the subsequent tsunami. The plant blackout as well as loss of dc power caused malfunction of plant coolability and then induced nuclear fuel melt and released massive fission products to the atmosphere due to failure of confinement and hydrogen explosion at reactor building. The design of Fukushima Daiichi nuclear power plants and the progression of the event will be summarized. Challenges of the safety design against this event will be discussed and then some actions to enhance the nuclear safety will be proposed following the lessons learned from the Fukushima event.

並列關鍵字

nuclear safety ； common failure ； station blackout ； Fukushima nuclear accident ； earthquake and tsunami

參考文獻

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