????日本今年遭受的9.0級大地震引發了一系列后續災難，包括3月11日的海嘯，以及日前的7.1級余震，還有此次福島核危機。福島核危機在人類的核安全史上又寫下了重重的一筆。自核能誕生以來，全球已經經歷了多次重大核事故，這些事故全都源于人為過失、安全規程不到位或設備老舊等因素，或是由幾種因素綜合造成的。

????在破損的核反應堆完全冷卻并被封堆之前，我們無法確知這次日本核危機的破壞范圍，甚至可能等到封堆后也無法知道。現在海嘯已經過去近一個月了，但對于事故現場——東京電力公司（Tokyo Electric Power Company）的福島第一核電站（Fukushima Daiichi Nuclear Power Station）究竟發生了什么，日本政府還是只披露了極少的消息。不過據悉該公司的工人仍在試圖冷卻破損的核反應堆。據國際原子能機構（IAEA）稱，東京電力公司將向太平洋排放超過1萬噸的低放射性污水。

????最終，國際原子能機構會對日本核危機的嚴重性進行評級。這套評級標準稱作“國際核事件分級表”（INES），是一套根據核事故的嚴重程度對核事故進行分級的機制，最低為1級，最高為7級。

????其中1級用來表示“異常”，例如某人接觸到的輻射水平高于監管機構規定的正常年照射量，但這種輻射水平不一定會引發健康問題。

????“異常”也可能意味著核設施的某個安全問題本可能造成更大的破壞，但結果并未造成嚴重后果；或是放射性材料被盜，或被不當運輸。例如，2006年在美國德克薩斯，有一名駕駛福特（Ford）卡車的司機把車鑰匙忘在了車上，結果車里的一臺50鎊重的放射線照相機被盜了，幾天后又被重新找到。這起事件就被認定為國際核事件分級表的1級事故。

????2級被稱為“一般事件”，3級稱為“重大事件”。一起核事故究竟應該被評為2級還是3級，取決于它造成了多大范圍的安全問題，以及遭到輻射的人數，和他們遭受的輻射劑量。

????國際核安全事件分級表的4到7級則被官方稱為“事故”，它們往往表示有一人或多人因遭受輻射而死亡——但也并非總是如此。國際核安全事件分級表并不涵蓋因非放射性化學品泄露或爆炸所導致的核設施人員傷亡。

????日本在1999年就曾發生過一次4級核事故（又稱“東海村核事故”——譯注），當時在日本核燃料轉換公司（Japan Nuclear Fuel Conversion）的一個燃料廠內，三名正在為反應堆準備燃料的工人引發了一次鏈式核反應，使反應堆達到臨界狀態。其中兩名工人最終死于輻射病。事后調查顯示，這家公司在事故發生三年前簡化了核燃料準備的工作流程，但增加了導致核臨界狀態的可能性。

????到本文撰寫時為止，本次福島核災難的評級還是5級，這表明反應堆堆芯已經受到嚴重損壞，而且公眾可能將受到某種程度的核輻射。

????1979年美國著名的“三里島核事故”評級也是5級，事故發生在美國賓夕法尼亞州首府哈里斯堡附近的一座核電站，當時這座核電站屬于大都會愛迪生公司（Metropolitan Edison）所有，不過現在該核電站已歸入艾克斯龍公司（Exelon Corporation）旗下。在“三里島核事故”中，該核電站出現了一次機械故障，導致其中一座反應堆運行過熱，進而自動關閉。核電站的操作人員對情勢反應不當，停止對反應堆進行冷卻，導致反應堆過熱而破損，并將放射性材料釋放到核電站內。

????美國核管理委員會的一份報告指出：“這次事故說明聯邦政府和州政府的警惕松懈”。該報告將三里島核事故歸咎于“個人過失、設計缺陷和部件故障的綜合因素”。

????三里島核事件并未導致人員死亡，不過它造成的破壞和清理費用卻高達近10億美元。

????史上第二嚴重的核事故發生在前蘇聯克什特姆省的馬雅克核燃料處理廠。1957年，該廠的一個裝有放射性廢料的容器發生了爆炸，該事故被國際核事件分級表評定為6級。據世界核協會（WNA）稱，馬雅克核爆炸向大氣中噴出了大約75噸放射性廢料，并且估計導致了200人罹患了致命的癌癥。

????第7級“特大事故”只有一起，當然，這就是切爾諾貝利核事故。切爾諾貝利位于現在的烏克蘭。事故發生于1986年，該核電站的一個反應堆本身就存在缺陷，事故發生時，核電站的操作人員忽視了安全規程，關閉了控制該反應堆的電氣控制系統，然后這個反應堆達到了不穩定狀態。

????功率的激增引起了反應堆的鏈式反應，反應堆的堆芯燃燒起來。它整整燃燒了10天，產生的放射性物質云籠罩了前蘇聯的大片地區。

????134名搶險工人暴露在大劑量的輻射之下，其中28名工人就在這一年內死于輻射病。

????除了30人左右的直接死亡外，切爾諾貝利事故還導致了許多人間接死亡，例如有些人的死可能是由輻射云導致的。據估計，切爾諾貝利事故形成的輻射云使500多萬人受到了異常劑量的照射。

????兒童尤其是這起核事故的犧牲品。根據一份由國際原子能機構、世界衛生組織（World Health Organization）、俄羅斯、白俄羅斯以及烏克蘭政府等幾方面共同起草的報告，截止到2002年，大約有4000名在1986年還是兒童的人因遭受切爾諾貝利事故的輻射，而患上了甲狀腺癌。還有許多兒童因飲用了被污染地區產出的含放射性物質的牛奶而罹患了癌癥。

????該報告指出，切爾諾貝利核事故導致的總體死亡人數仍不確定，“要可靠、精確地計算因遭受切爾諾貝利核事故的輻射而罹患癌癥的人數是不可能的。”

????2010年經濟合作與發展組織（OECD）和核能機構（Nuclear Energy Agency）聯合發布的一份報告含蓄地表達了一個觀點，即能源工業的核事故所導致的死亡人數不應被夸大。該報告指出，在1969年到2000年間，有2259人死于與煤炭業相關的事故，另有3713人死于與石油工業相關的重大事故。

????盡管如此，這次日本核事故還是促使一些政治領導人暫停了核電項目的進展。例如德國和中國的政府官員都在重新評估本國新建核電項目的審批手續。

????不過，這并不意味著核電項目從長遠看來將減少。國際能源署（International Energy Agency）在 《2010年世界能源展望》（World Energy Outlook）中預測道，從2008年到2035年，世界初級能源需求將增長36%，與此同時，核能占能源構成的比重將由6%增長至8%。

????無疑，世界仍將需要更多的能源。日本核危機迫使監管機構和能源企業直面這一代人最大的挑戰：如何在滿足激增的全球能源需求的同時，保證人們的安全。

????譯者：樸成奎

????FORTUNE -- The nuclear crisis in Japan, the aftermath of an 9.0 magnitude earthquake, including a 7.1 magnitude aftershock yesterday, and a tsunami on March 11, adds to a long list of major nuclear accidents, all of which stem from some combination of human error, insufficient safety procedure, or outdated equipment.

????We won't know the extent of the damage from this nuclear crisis until well after the ruined reactors are cooled and buried, maybe not even then. Even now -- 28 days after the tsunami -- Japan's government has disclosed very little information about what has happened at the scene of the accident, the Tokyo Electric Power Company's (TEPCO) Fukushima Daiichi Nuclear Power Station. Workers there, however, are known to be still trying to cool the damaged reactors. According to the International Atomic Energy Agency (IAEA), TEPCO will have to release over 10,000 tons of low-level radioactive water into the Pacific Ocean.

????Eventually, this Japanese incident will be assigned a final numerical rating according to a scale devised by the IAEA. The scale, called INES (for International Nuclear and Radiological Event Scale), breaks down the severity of nuclear events into bloodless, regimented categories. Each event ultimately gets a ranking from 1 to 7.

????A rating of 1 is applied to "an anomaly." That includes situations in which a person is exposed to a higher level of radiation than the annual limit set by regulators, but does not necessarily develop health problems.

????An "anomaly" can also mean that a safety problem at a facility could have resulted in greater damage than it did or that radioactive material has been stolen or transported incorrectly. For example, in Texas in 2006, the driver of a Ford truck containing a 50-pound radiography camera left his keys in the truck. It was stolen and then found a couple of days later. This incident rated a 1 on the INES scale.

????Level 2 is an "incident" and Level 3 is a "serious incident." Which designation applies depends on the extent of security problems, the number of people exposed to radiation, and the dosage they receive.

????Levels 4-7 on the INES scale are officially called "accidents" and often, but not always, signal that one or more fatalities from radiation exposure have occurred. The INES ranking scale doesn't cover deaths at nuclear facilities from non-radioactive chemical leaks or explosions.

????Japan itself had a Level 4 accident in 1999, when three workers preparing fuel for a reactor at a Japan Nuclear Fuel Conversion plant triggered a nuclear chain reaction, called a criticality. Two workers subsequently died. An investigation of the accident found that the company had changed its work procedures for preparing nuclear fuel three years earlier, streamlining these but also increasing the likelihood of their causing a criticality.

????Today's Japanese nuclear disaster is for the moment rated level 5, which signifies that there is severe damage to the reactor core and that members of the public will probably be exposed to some level of radiation.

????Level 5 is also the designation for America's infamous 1979 event known as Three Mile Island, denoting a facility near Harrisburg, Pennsylvania that was owned by Metropolitan Edison (Exelon Corporation owns it now.) In this crisis, a reactor at the plant automatically shut down in response to a malfunction that caused it to run too hot. The plant's operators responded incorrectly to the situation and stopped cooling the reactor, which overheated, suffered damage, and released radioactive material inside the plant.

????"The accident caught federal and state authorities off-guard," said a report by the United States Nuclear Regulatory Commission, which attributed the accident to "a combination of personnel error, design deficiencies, and component failures."

????No one died at the Three Mile Island accident, but the facility incurred nearly $1 billion of damages and clean-up costs.

????History's second-most damaging nuclear accident occurred in 1957 at Russia's Mayak plant in the Kyshtym province. Caused by the explosion of a tank that contained radioactive waste, this crisis is recorded as a Level 6 "serious accident" on the INES scale. The explosion spewed roughly 75 tons of radioactive waste into the atmosphere, according to the World Nuclear Association, and caused an estimated 200 people to develop fatal cancer.

????There has only been one Level 7 "major accident," and that, of course, was at Chernobyl, located in what is now called Ukraine. This disaster occurred in 1986 when operators, ignoring safety regulations, switched off the electrical control system governing a reactor that was already flawed. The reactor then proceeded to reach an unstable state.

????A surge of power caused a chain reaction that set the reactor core on fire. It burned for 10 days and released a cloud of radioactive matter that spread over a wide area of the USSR.

????At the plant, 134 emergency workers were exposed to high doses of radiation that killed 28 of them in that same year, 1986.

????To that toll of about 30 deaths must be added the indirect effects of Chernobyl—deaths caused, for example, by that radioactive cloud, which is estimated to have exposed more than 5 million people to abnormal doses of radiation.

????Children were particular victims. Around 4000 people who were children in 1986 had by 2002 developed thyroid cancer from the exposure, according to a report issued jointly by several parties including the IAEA, World Health Organization and the governments of Russia, Belarus and Ukraine. Many of the children developed cancer from drinking irradiated milk produced at dairies in the contaminated area.

????The overall death toll from Chernobyl remains uncertain, says that same report: "It is impossible to assess reliably, with any precision, numbers of fatal cancers caused by radiation exposure due to Chernobyl accident."

????The death toll from nuclear events in the energy industry should not be overstated, a point implicitly made in a 2010 joint report by the OECD and the Nuclear Energy Agency. The report states that 2,259 people in the OECD's 32 countries died from coal industry-related accidents between 1969 and 2000 and that 3,713 people died from major oil industry-related accidents during the same period.

????Even so, Japan's accident has caused some political leaders to pause the progression of nuclear power. Government officials in Germany and China, for example, are reassessing their countries' approval process for new nuclear projects.

????That doesn't mean there will necessarily be a long-term diminution in nuclear projects. The International Energy Agency's World Energy Outlook for 2010 predicts that primary energy demand will grow by 36% between 2008 and 2035 and that nuclear power's share of the energy mix will meanwhile increase from 6% to 8%.

????Indisputably, the world will continue to need more fuel. The nuclear accident in Japan casts into sharp relief the pressure on regulators and energy producers to face one of this generation's greatest challenges: meeting the spiking global energy demand while simultaneously keeping people safe.