跟他說核四廠商能力的問題
核災陰影籠罩下 Kawase 先生短信報平安
仙貝的日本-台灣故事
上周的狀況 包括美國的科技偵測 日本核災..
---
2011年 03月 22日 08:00
福島核事故之後的核安全反思
CHRISTOPHER STEPHENS
儘
管 日本福島第一核電站仍然處於不穩定狀態﹐但目前關注的焦點已經從控制轉向評估。強達9.0級的地震、成百上千次餘震以及由此引發的海嘯都已經成為過去。但 是﹐這些都不能說是不可預見的事件﹐這也正是此次事故給全球監管機構提出的一系列重要問題的核心所在：核安全監管機構應該在多大程度上考慮所有可預見的意 外事件？那些按照原先的行業標準建造的已有設備是否需要採用新的技術？相關報導
由此帶來的過熱問題導致壓力升高至設計極限的兩倍多﹐並導致三個反應堆爆炸。根據設計﹐用於包裹反應堆的週邊建築能夠經受惡劣天氣狀況的考驗﹐但承受不了氫爆炸的衝擊。爆炸導致放射性物質外泄﹐使人們普遍擔憂身體健康和環境受到威脅。
雖然這一系列事件都非同尋常﹐但不能說是不可預見的。日本的基礎設施和監管架構預先考慮了未來150年可能發生的地震﹔供電中斷、海嘯以及考驗應急能力的各種需求都是可預見的地震後果。
事 實上﹐工程師們已經設計出了能夠減輕風險的解決方案﹐雖然對福島核電站來說這些風險已經不幸成為現實。如今的第三代核反應爐考慮了冷卻泵系統失靈和氫壓增 大的可能性。美國西屋電氣(Westinghouse)建造的AP1000反應堆擁有一系列不需要外部電源或柴油發電機的被動冷卻系統﹐也不需要操作人員 起動。這個反應堆還配備了防止氫爆炸的複合裝置。
DigitalGlobe/Getty Images
日本福島第一核電站
那麼﹐這些新技術為什麼沒有被應用於福島核電站呢？全球各國的核安全監管機構都要根據將被採納的技術、場所和一系列可能威脅設備安全及控制的事件來評估核電設備的相關風險。即使是在核電廠建成之後﹐監管機構還有廣泛的權力對某個電站的設備、系統和程式追加更多要求。
問 題是﹐監管機構怎樣決定何時要求電廠運營商對舊廠進行代價不菲的技術更新呢？這正是日本監管機構在進行合理審查時最終可能觸及的問題。這既是一個工程技術 問題﹐也是一個成本效益分析問題。雖然核電站的某些模組設備和控制系統可以進行升級﹐但由於存在輻射﹐反應堆週邊建築的主體部分不能被輕易移除、處置或替 換。
這就意味著在某些情況下面臨的選擇就不是核電站升不升級的問題﹐而是是否徹底關閉的問題了。考慮到這種選擇﹐運營商和監管機構往往會 維持現狀不變﹐而不會要求舊電廠採用較新的系統以便更有效地解決看似遙遠的風險。福島核事故也許會促使日本乃至全球各國都重新考慮上面這種處理辦法。
日 本的經驗還表明﹐監管機構和緊急規劃部門需要更加現實地考慮可能引發緊急狀況的各種情況。大多數核安全監管規定都是基於這樣一種假設：只會在某一座核電站 發生某一種災難（類似切爾諾貝利(Chernobyl)核事故和三里島(Three Mile Island)核事故）﹐由電站內部或外部環境引發的事故只會影響電站週邊地區。
這種規劃方法可能使各國當局在類似福島核洩漏這樣的重大 自然災害中的核事故發生時措手不及。在仙台地震發生後﹐應急人員和救災物資需要覆蓋到35,000平方英里的區域﹐在這個區域內﹐有兩百萬人陷入斷水斷電 和食品短缺危機﹐道路、機場和其他基礎設施被嚴重損毀。如果事前進行了更有遠見的規劃﹐應該已經預料到這種環境下應急服務的侷限性。
最後 ﹐監管機構還需要考慮社會和特定的文化因素。日本雄厚的財力、先進的技術和高品質的基礎設施使其出色地抵禦了強烈的地震和可怕的海嘯帶來的破壞。素以自律 聞名的高素質的國民無疑也幫助了日本免於陷入末日般的災難後果。雖然這不能阻止福島事故的發生﹐但確實意味著這個國家在應對此類事件時可能要比其他國家準 備得更好。
越南、馬來西亞、泰國、菲律賓、印尼以及其他位於太平洋斷層線上的有志開發核能的國家都需要認真評估本國應對類似情況的能力。即使不考慮災前規劃的品質問題﹐他們是否有足夠的資源來應對類似福島的事故？
在未來的某個時候﹐即使是目前正在籌畫中的最先進的核電系統與那時的最新技術相比也會顯得落後。福島核事故應該使現在和將來的監管機構都停下來深思一下﹐他們在面臨技術革新的時候應該如何對待安全問題？
（編者按﹕本文作者CHRISTOPHER STEPHENS為律師事務所Orrick, Herrington and Sutcliffe的高級合夥人。）
Nuclear Safety After Fukushima
CHRISTOPHER STEPHENS
Even with events at Japan's Fukushima Daiichi nuclear power complex still in a state of flux, attention is shifting from containment to assessment. The 9.0 magnitude earthquake, hundreds of aftershocks and ensuing tsunami were historic. But they can hardly be called unforeseeable, and therein lies the nub of the critical questions this incident will raise for regulators everywhere: To what extent should nuclear safety regulation take account of all foreseeable contingencies, and should new technologies be required to apply to pre-existing facilities that were built to the standard of the industry at the time of construction?
The six-reactor Fukushima Daiichi facility was commissioned in 1971 and—by design—successfully withstood the March 11 earthquake and its aftershocks. But the tsunami topped the facility's sea wall, knocking out the back-up diesel generator and forcing the pump cooling systems and pressure ventilators to rely on batteries until mobile generators could be delivered to the site. Water also flooded the basement where switching equipment connected the pumping equipment, impeding repairs.
The result was overheating that caused pressure to build to over two times the designed limitations and led to explosions at three of the reactors. The outer buildings were designed to contain the reactor and to withstand severe weather conditions, but not hydrogen explosions. Radiation leakages resulted, causing widespread concerns about threats to health and the environment.
Such a chain of events, however extraordinary, cannot be said to be unforeseeable. Japan's infrastructure and regulatory framework have anticipated earthquakes for 150 years; power outages, tsunamis and widespread demands that strain response efforts are all predictable consequences of earthquake risk.
Indeed, engineers have already designed solutions to mitigate the risks that materialized at Fukushima. Today's third-generation nuclear reactors anticipate the possibility of failed cooling systems and hydrogen pressure build-ups. The Westinghouse AP1000 reactor has a series of passive cooling systems that operate without external or diesel-generated power or activation by its operators. It also has recombiners that prevent hydrogen explosions.
This design has been officially adopted in China for all inland nuclear projects where earthquake risks are more prevalent than on its coasts. Areva's EPR reactor under construction in Finland, France and China has four independent emergency passive cooling systems and extra core containment areas around the reactor. And Mitsubishi's new APWR has passive and active redundant cooling systems.
So why weren't these technologies installed at Fukushima? Nuclear safety regulators around the world assess risks associated with nuclear power facilities on the basis of the technology to be deployed and the location and range of events that potentially could threaten the safety or control of the facility. Even after construction, regulators are given wide discretion to impose additional requirements on the equipment, systems and procedures used at a given facility.
The problem is how to decide when to require plant operators to implement costly refits of new technology on older plants—and this is where Japan's regulators could ultimately come in for some justifiable scrutiny. This is a question of both engineering and cost-benefit analysis. While certain modular equipment and control systems in nuclear plants can be upgraded, integral parts of the reactor chamber or housing cannot be easily removed, disposed of and replaced due to the presence of radioactivity.
This means that in some cases the choice may not be whether or not to upgrade, but whether to shut down entirely. Given those options, operators and regulators are inclined to maintain the status quo instead of requiring the application to old facilities of newer systems to more effectively address risks that can seem quite remote. Fukushima may cause a rethink of this approach not only in Japan but around the world.
Japan's experience also suggests regulators and emergency planners need to think more realistically about the circumstances under which an emergency is likely to occur. Most nuclear safety regulations are based on a scenario where a singular disaster occurs at a specific facility—akin to Chernobyl or Three Mile Island, incidents that arose due to circumstances within the plants themselves or external events affecting their immediate vicinity.
That approach to planning can leave officials unprepared for what has happened at Fukushima: a nuclear incident as part of a much larger disaster. In the aftermath of the Sendai earthquake, response teams and resources were required to cover an area of 35,000 square miles, in which two million people were without power, water or food, and roads, airports and other infrastructure were severely damaged. More far-sighted planning would have anticipated the limitations on emergency services in such circumstances.
Finally, regulators need to account for the societies and particular cultures they cover. Japan's great wealth, technological advancement and quality infrastructure made it remarkably resistant to the ravages of a great earthquake and horrific tsunami. And the high levels of education and the renowned discipline of its people certainly helped it avoid apocalyptic consequences. While this hasn't averted the problem at Fukushima, it does mean the country was better equipped to deal with such an event than others might have been.
Regulators in Vietnam, Malaysia, Thailand, the Philippines, Indonesia and other developing nuclear aspirants that ring the fault lines of much of the Pacific Ocean need to candidly assess their nation's capacity to respond in similar circumstances. Would they have the resources to deal with a Fukushima-style incident, even apart from any question about the quality of pre-disaster planning?
At some point in the future even the most modern nuclear power systems on today's drawing boards will appear antiquated compared to the day's technology. Fukushima should give regulators both today and tomorrow pause in how they approach the issue of safety in the face of technological evolution.
(Mr. Stephens is a Hong Kong-based senior partner with the law firm Orrick, Herrington and Sutcliffe. )
沒有留言:
張貼留言