MIT 福島核災lessons learned

2011/07/26 麻省理工學院核子科學與工程系專家發表的報告
http://mitnse.files.wordpress.com/2011/08/fukushima-lessons-learned-mit-nsp-025_rev1.pdf

作者包含以下九位(很多是MIT核工土生土長的 1-3次方)：
J. Buongiorno, R. Ballinger, M. Driscoll,
B. Forget, C. Forsberg, M. Golay,
M. Kazimi, N. Todreas, J. Yanch

從技術的角度來反省這樣一個災難的發生，從學到的教訓來思考如何預防和改善

摘要報告的頭尾部份內容，試著評論與揣測這些人的思維模式(或許這些靠核能吃飯的聰明人，在心態上必須為自己的專業辯護)

Disclaimer: 以下僅為台籍半調子工安外行的個人報告觀摩心得，請讀者注意

報告摘要：
Premise
First, the accident was a result of the worst earthquake and tsunami in Japan’s modern history, an event which has caused the loss of over 20,000 lives and up to $300 billion in damages.
Second, given the extraordinary magnitude of the initiating events (i.e. earthquake was 9.0 vs design 8.2, tsunami wave was 14 m vs design 5.7 m), the Fukushima-Daichii plant has performed relatively well in some respects and so far there is no evidence of major human errors in handling the crisis.   It is noted that the containments at Units 1-3 have not massively failed, in spite of the exceptional loads they have been subject to, i.e. earthquake, tsunami, hydrogen explosions in the reactor buildings, steam discharges from the reactor pressure vessel, exposure to hot seawater, pressure above design limits for days. The release of radioactivity from the plant has been large (with contributions also from containment venting) and some workers have received significant radiation doses (>100 mSv whole-body equivalent), but health risks for them and the general population are expected to be negligible (see Appendix A). In fact, no loss of life has occurred or is expected as a result of the accident. Direct damage and casualties inflicted on Japan by the earthquake and tsunami far exceed any damage caused by the accident at the nuclear plant. The Fukushima accident has been rated at the maximum level (Level 7) on the IAEA nuclear event scale, indicating an accident with large
release of radioactivity accompanied by “widespread health and environmental effects”, like Chernobyl. However, there are very significant differences between Fukushima and Chernobyl.
Briefly, the amount of the release (~10% of Chernobyl), the presence of the containment structures, the radionuclides released (mostly iodine and cesium isotopes vs. the entire core inventory), the physical form of the releases (mostly aqueous vs. volatile), the favorable currents and winds at the site, and the timing of the release with respect to population evacuation resulted in vastly smaller overall consequences. Having said this, it is important to analyze the technical lessons that can be learned from Fukushima, so that the safety of nuclear plants in the U.S. and worldwide can be further enhanced and the attractiveness of nuclear energy sustained over the long term.

從這群專家的眼中看來，千錯萬錯都是意想不到天災的錯=>當初設計得抗震強度是8.2，結果實際遭遇到了9級的強震；抵擋海嘯的設計高度是 5.7米，結果實際遭遇的海嘯高度是14米
意謂著沒有設計上的業務過失？！

報告內容編排如下

A few closing thoughtsThe initial response of the nuclear industry and the U.S government to the Fukushima accident has been measured and rational (see Appendix B). However, the risk of over-reacting to an accident, particularly one as dramatic as Fukushima, remains high. The industry is concerned about the near-term effect of Fukushima on the process of life extension of current plants and the support for new construction projects. Under the pressure of the public and the media, the government may be compelled to push for sweeping policy and regulatory changes, which may ultimately prove to be unnecessarily onerous on existing and future plants. Decision-making in the immediate aftermath of a major crisis is often overly influenced by emotion. Therefore, the following questions should be addressed after searching for vulnerabilities at existing plants, but before enacting significant changes in nuclear energy regulations and policy. Does an accident like Fukushima, which is so far beyond design basis, really warrant a major overhaul of current nuclear safety regulations and practices? The answer is country-dependent; for example, the design-basis selection process for tsunamis in Japan will likely require some significant changes, in particular regarding the use of historical tsunami “data” in estimating the risk of future large tsunamis. However, the critical question is: how, in the design-basis selection process, do we establish when safe is safe enough? Where do we draw the line? It seems that a rational approach to this question would ultimately need to be based on a risk-informed
comparison of nuclear energy with other energy sources (particularly its most credible competitors, such as coal and natural gas), including their effects on climate change, global economy, stability and reliability of the energy supply, and geo-politics. But can the decision makers take a risk-informed approach to energy policy?
When it comes to safety, it is important to bear in mind that all engineered structures (e.g. power plants, bridges, skyscrapers, dams, highways) will fail if subjected to loads far enough beyond what they were designed for. Are the design basis selections of energy industry structures posing high environmental hazard, such as oil drilling platforms offshore, coal mines and water dams, consistent with those of nuclear plants? If not, are we as a society irrationally accepting higher risks from certain technologies than others?

欸，最後一段話讓人看出這些專家心中的失衡與情緒了

----------------------------以下為外行人不負責任的報告評論---------------------------

先說這份報告的優點：

1. 簡短明確，只有十幾頁，也直接點出問題核心在於=>發生超過設計標準的意外天災是造成事故的主因
2. 依據幾個issue(備用緊急電力、異常事故反應、氫氣控管、污染圍堵、使用後燃料、廠址)，從事件觀察到的狀況=>需注意深思的問題=>現有廠的改善對策=>未來新廠設計時的注意重點
3. MIT不愧是MIT，也只有真正一流的核工人，會以天下核子安全為己任，在這樣重大事件之後，跳出來寫這樣的反省和lessons learned報告公諸於世(還是有拿相關經費就不得而知了.. )

再來談一些個人愛之深責之切的期許和想法

1. 風險的不確定：從報告的最後一段，可以看出風險管理VS經濟效益的決策兩難=>可以把電廠設計規格拉高到耐震十級與海嘯20米，只是預期的發生機率太低、所需的經費是天價；就這些專家來看，要求現有運轉電廠與未來電廠要依據福島核災情境去加強改善，(這些專家他們覺得)或許會是過度反應；只是在可預期的將來，一定還會有這種黑天鵝事件發生(讓抱持上述觀念的專家大感意外..)
2. 統計常態分布觀念的餘毒：不知這些專家在看待意外與計算極端事件的發生機率時，其心智模式與數學工具基礎是否為常態分布，如果是的話，將來這些黑天鵝事件的發生機率會比他們期望的高很多...

3. MIT核工的自我定位與期許：它們家的slogan是 Science/System/Society 。從這個報告，敝人只有看到前兩者，Society的部份比較被忽略了(沒有站在一般大眾的感受和角度)；管理與技術是工安與風險管理一體的兩面，不能偏廢！但主事者理學院或工學院的學校訓練背景，導致其思維存在(偏談工程/硬體設備/線性邏輯思維)偏誤而不自知。