2011年3月16日 星期三

日核電廠6級意外事故(福島第1核電廠1號機)InternationalNuclear and Radiological Event Scale,INES


16 日

外電報導，法國核能安全局(ASN)局長Andre-Claude Lacoste 15日指出，日本福島核電廠事故目前在國際核能意外事故分級當中已達第6級的程度。1979年美國賓州的三浬島(Three Mile Island)事件為5級，1986年烏克蘭的車諾比(Chernobyl)事件則達最高的7級。 ...

福島第一原発、待避範囲２０キロ圏内に拡大

2011年3月12日19時11分


ss 写真：福島第一原子力発電所＝１２日午前９時５２分、朝日新聞社ヘリから、山本裕之撮影拡大福島第一原子力発電所＝１２日午前９時５２分、朝日新聞社ヘリから、山本裕之撮影

写真：福島第一原子力発電所＝１２日午前９時４７分、福島県、朝日新聞社ヘリから、山本裕之撮影拡大福島第一原子力発電所＝１２日午前９時４７分、福島県、朝日新聞社ヘリから、山本裕之撮影

図：福島第一原発、避難指示２０キロ圏内に拡大福島第一原発、避難指示２０キロ圏内に

写真：「燃料が溶け出していると見ていい」と硬い表情で発表する経産省原子力安全・保安院の担当者ら。ホワイトボードには「炉心溶融」の文字が＝経産省拡大「燃料が溶け出していると見ていい」と硬い表情で発表する経産省原子力安全・保安院の担当者ら。ホワイトボードには「炉心溶融」の文字が＝経産省

　経済産業省の原子力安全・保安院は１２日、東日本大震災で被害を受けた東京電力福島第一原子力発電所１号機（福島県大熊町）で、午後３時３０分ごろに大 きな爆発音を伴う爆発が起きたことを明らかにした。その直前には、原子炉内の燃料の溶融が進んでいる可能性が高いと発表しており、原子炉の状態と爆発との 関係を含め、東電などが原因を調査中だ。

　放射線医学総合研究所や東電が原発敷地内で、燃料中に含まれる核分裂生成物であるセシウムやヨウ素を確認した。いずれも、ウランが核分裂をした後にできる物質だ。

　炉心溶融は、想定されている原発事故の中で最悪の事態だ。これが進むと、爆発的な反応を引き起こして広く外部に放射能をまき散らす恐れもある。

　爆発音について、枝野官房長官は１２日夕の会見で「原子炉そのものであるということは確認されていないが、なんらかの爆発的事象があったと報告された」 と述べた。福島県によると、爆発で１号機の原子炉建屋の天井が崩落したことを確認したという。東電社員ら４人が負傷し、病院に搬送されたという。

　東京電力は１２日午後、同３時３０分ごろ現場敷地境界で１時間あたり１０１５マイクロシーベルトの放射線を確認し、その２分後にはほぼ半減したと発表し た。１０１５マイクロシーベルトは、一般人の年間被曝（ひばく）線量の限度（１ミリシーベルト＝１０００マイクロシーベルト）を、１時間で浴びる放射線量 に該当する。

　日常生活で自然から浴びている放射線は平均で１時間あたり０．２７マイクロシーベルト。放射線業務従事者は年間５０ミリシーベルトかつ５年間で１００ミリシーベルトが被曝限度とされている。

　政府から待避指示が出た原発から１０キロ圏内には約８００人の住民が残っていたが、午後６時現在も避難中という。

　一方、保安院によると、爆発音のあった後に、１号機の原子炉格納容器の圧力が急激に下がってきたという。格納容器の破損を防ぐため、弁を開けて内部の空 気を抜く作業が効果を上げたのか、他の要因かは不明だ。空気とともに容器内の放射性物質も外部に放出されたとみられ、放射線の観測値は上昇している。

　原子炉圧力容器内の水位は下がり続けており、午後５時２８分の段階で、燃料棒（長さ４メートル）の上端から１．７メートル低い位置にある。燃料棒の半分 近くが露出した状態になっている。消防車などを使って冷却水を注入しているが追いついていない。このため、東電は海水も使うことを選択肢の一つとして検討 していることを明らかにした。

　政府は福島第二原発（同県楢葉町、富岡町）について、避難を指示する範囲を、半径３キロ圏から１０キロ圏に拡大した。その後、官邸は第一原発から待避を指示する範囲を、半径１０キロから２０キロに拡大した。

　　　　◇

　炉心溶融　原子炉内の水位が下がり、炉心が水中から露出すると、燃料の温度が上昇し、燃料を入れた金属製の器（被覆管）が溶ける。冷却が不十分だと燃料 の溶融から、さらに炉心の構造物の破壊と落下が起こる。ここに水があると、水と溶融物が接触し急激な爆発が起こる恐れがある。爆発で格納容器が破壊されれ ば、大量の放射性物質が環境に放出されることになる。




日核電廠爆炸 4級意外事故
2011/03/13 01:16:48 小型字 中型字 大型字

（中央社東京13日綜合外電報導）日本原子能安全保安院說，福島第1核電廠1號機12日發生氫氣爆炸事故，依國際核能事件分級表屬4級意外事故，嚴重程度 低於1979年三哩島核子事故以及1986年車諾比爾核子災變。

日本經濟產業省原子能安全保安院（Nuclear andIndustrial Safety Agency, NISA）雖指出，福島第1核電廠1號機反應爐的爐心破損機率相當高，但卻認為目前「並未發生爐心熔融持續進行情形」。

原子能安全保安院說，福島第1核電廠1號機發生的爆炸事故，依國際核能事件分級表（InternationalNuclear and Radiological Event Scale,INES）屬造成局部影響的4級廠區意外事故，與1999年茨城縣東海村核燃料加工業者JCO臨界事故不相上下。

INES的事故分級，從最輕微的0級至最嚴重的7級，共計8級，美國三哩島（Three Mile Island）核子事故屬5級，車諾比爾（Chernobyl）核子災變則是最嚴重的7級。

這次4級事故，也與東海村臨界事故並列為日本歷來最嚴重核子事故。


***


日 本福島核電廠在百年大震之後發生一連串事故，昨日上午先是傳出冷卻系統失靈，接著下午氫氣爆炸、幅射外洩，進入緊急狀態，台電從專業角度來看，反應爐爐心 只要有完整的「一次圍阻體」來保護，應該不致有發生燃料棒熔解的嚴重情形。日本福島核電廠的處理，就是在保護「一次圍阻體」的完整，這樣才能保護核能反應 爐。

核能電廠的事故發生時，反應爐通常會發生溫度持續升高情形，此時冷卻系統就要啟動，並將冷卻又打入爐心，以降低溫度。日本福島核電廠的事故就是冷卻系統因 為緊急發電機故障，無法將冷卻水打入爐心，致使爐心溫度持續升高。而為了降溫，就釋放蒸氣，接著才發生幅射放洩情形。而依規定，一人一天能承受的幅射量， 是1000微西氟(微西氟指的是人體每公斤接受加馬射線的能量計算單位)。

反應爐在溫度持續升高下，核電廠的設計會為了避免釀成更嚴重的災害，讓反應爐內的蒸氣釋壓，否則爐心可能會熔解；但釋壓時，就會有輻射溢出。

就因為要防範爐心熔解事故的發生，台電在核能電廠在安全設計上採取縱深防禦該計，如果爐心溫度無法降低時，「硼液」系統會緊急啟動，將「硼液」打入爐心，來吸收中子反應，讓核子反應停下來。

核能電廠最怕爐心熔毀，所以除了控制棒在緊急事故發生時，要插入爐心讓核子反應停止外，也需要有冷卻系統要讓爐心降溫，免得爐心若一再升高，可能會導致爐心熔解，釀成最嚴重核子事故。

由於核子事故發生，通常都是逐漸性嚴重，所以核能主管單位會就核子事故發生情況的嚴重程度，決定是否進行附近民眾的緊急疏散。

若進行民眾的緊急疏散，即表示核電廠的核子事故相當嚴重。udn晚報




***

InternationalNuclear and Radiological Event Scale,INES


The International Nuclear and Radiological Event Scale (INES) was introduced in 1990[1] by the International Atomic Energy Agency (IAEA) in order to enable prompt communication of safety significance information in case of nuclear accidents.

The scale is intended to be logarithmic, similar to the Richter scale that was used to describe the comparative magnitude of earthquakes. Each increasing level represents an accident approximately ten times more severe than the previous level. Compared to earthquakes, where the event intensity can be quantitatively evaluated, the level of severity of a man-made disaster, such as a nuclear accident, is more subject to interpretation. Because of the difficulty of interpreting, the INES level of an incident is assigned well after the incident occurs. Therefore, the scale has a very limited ability to assist in disaster-aid deployment.

Commonly, the organisation where the nuclear incident occurs assigns a first provisional INES rating to an incident, after it is being reviewed and possibly revised by the designated national radiation authority.

A number of criteria and indicators are defined to assure coherent reporting of nuclear events by different official authorities. There are 7 levels on the INES scale; 3 incident-levels and 4 accident-levels. There is also a level 0.

7 – Major Accident
6 – Serious Accident
5 – Accident With Wider Consequences
4 – Accident With Local Consequences
3 – Serious Incident
2 – Incident
1 – Anomaly
0 – Deviation (No Safety Significance)
Contents

Details

The level on the scale is determined by the highest of three scores: off-site effects, on-site effects, and defence in depth degradation.

INES Level 7: Major accident

Impact on People and Environment
Major release of radio­active ­material with widespread health and environmental effects r­equiring implementation of planned and extended ­countermeasures

Example:

  • Chernobyl disaster, 26 April 1986. A power surge during a test procedure resulted in a criticality accident, leading to a powerful steam explosion and fire that released a significant fraction of core material into the environment, resulting in a death toll of 56 as well as estimated 4,000 additional cancer fatalities among 600,000 people exposed to elevated doses of radiation [2] and a permanent loss of large areas of habitable land. The disaster is the only Level 7 Event that has ever occurred.

INES Level 6: Serious accident

Impact on People and Environment
Significant release of radioactive material likely to require implementation of planned countermeasures.

Example

  • Kyshtym disaster at Mayak, Soviet Union, 29 September 1957. A failed cooling system at a military nuclear waste reprocessing facility caused a steam explosion that released 70-80 tons of highly radioactive material into the environment. Impact on local population is not fully known.[3]

INES Level 5: Accident with wider consequences

Impact on People and Environment
Limited release of radioactive ­material likely to require i­mplementation of some planned­ countermeasures.
Several deaths from ­radiation.

Example: Windscale fire (United Kingdom), 10 October 1957. Annealing of graphite moderator at a military air-cooled reactor caused the graphite and the metallic uranium fuel to catch fire, releasing radioactive pile material as dust into the environment.

Impact on Radiological Barriers and Control
Severe damage to reactor core.
Release of large quantities of radioactive material within an installation with a high probability of significant public exposure. This could arise from a major criticality accident or fire.

Example: Three Mile Island accident (United States), 28 March 1979. A combination of design and operator errors caused a gradual loss of coolant, leading to a partial meltdown. Radioactive gases were released into the atmosphere.

Other examples:

  • First Chalk River Accident Chalk River, Ontario, Canada, 12 December 1952. Reactor core damaged. Future U.S. President Jimmy Carter was part of the cleanup crew.
  • Goiânia accident (Brazil), 13 September 1987. An unsecured caesium chloride radiation source left in an abandoned hospital was recovered by squatters unaware of its nature and sold at a scrapyard. 249 people were contaminated and 4 died.

INES Level 4: Accident with local consequences

Impact on People and the Environment
Minor release of radioactive material unlikely to result in implementation of planned countermeasures other than local food controls.
At least one death from radiation.
Impact on Radiological Barriers and Control
Fuel melt or damage to fuel ­resulting in more than 0.1% release of core inventory.
Release of significant quantities of radioactive material within an installation with a high ­probability of significant public exposure.

Examples:

INES Level 3: Serious incident

Impact on People and Environment
Exposure in excess of ten times the statutory annual limit for workers.
Non-lethal deterministic health effect (e.g., burns) from radiation.
Impact on Radiological Barriers and Control
Exposure rates of more than 1 Sv/h in an operating area.
Severe contamination in an area not expected by design, with a low probability of ­significant public exposure.
Impact on Defence-in-Depth
Near accident at a nuclear power plant with no safety provisions remaining.
Lost or stolen highly radioactive sealed source.
Misdelivered highly radioactive sealed source without adequate procedures in place to handle it.

Examples:

INES Level 2: Incident

Impact on People and Environment
Exposure of a member of the public in excess of 10 mSv.
Exposure of a worker in excess of the statutory annual limits.
Impact on Radiological Barriers and Control
Radiation levels in an operating area of more than 50 mSv/h.
Significant contamination within the facility into an area not expected by design.
Impact on Defence-in-Depth
Significant failures in safety ­provisions but with no actual ­consequences.
Found highly radioactive sealed orphan source, device or transport package with safety provisions intact.
Inadequate packaging of a highly radioactive sealed source.

Examples:

INES Level 1: Anomaly

Impact on Defence-in-Depth
Overexposure of a member of the public in excess of statutory ­annual limits.
Minor problems with safety components with significant defence-in-depth remaining.
Low activity lost or stolen radioactive source, device or transport package.

(Arrangements for reporting minor events to the public differ from country to country. It is difficult to ensure precise consistency in rating events between INES Level-1 and Below scale/Level-0)

Examples:

  • Gravelines (Nord, France), 8 August 2009; during the annual fuel bundle exchange in reactor #1, a fuel bundle snagged on to the internal structure. Operations were stopped, the reactor building was evacuated and isolated in accordance with operating procedures. [5]
  • TNPC (Drôme, France), July 2008; leak of 6000 litres of water containing 75 kg of Uranium into the environment.

INES Level 0: Deviation

No safety significance.

Examples:

Out of Scale

There are also events of no safety relevance, characterized as "out of scale".

Examples:

  • 17 November 2002, Natural Uranium Oxide Fuel Plant at the Nuclear Fuel Complex in Hyderabad, India: A chemical explosion at a fuel fabrication facility[9]
  • 4 November 1999: H.B. Robinson, United States: A Tornado sighting within the protected area of the NPP[10].
  • 15 April 1999: San Onofre, United States: Discovery of suspicious item in nuclear power plant[10]

See also

References

  1. ^ "Event scale revised for further clarity". World-nuclear-news.org. 2008-10-06. http://www.world-nuclear-news.org/RS_Event_scale_revised_for_further_clarity_0510081.html. Retrieved 2010-09-13.
  2. ^ "IAEA Report". In Focus: Chernobyl. Archived from the original on 2007-12-17. http://web.archive.org/web/20071217112720/http://www.iaea.org/NewsCenter/Focus/Chernobyl/index.shtml. Retrieved 2006-03-29.
  3. ^ http://www.iaea.org/Publications/Factsheets/English/ines.pdf
  4. ^ G A M Webb et al. (March 2006). "Classification of events with an off-site radiological impact at the Sellafield site between 1950 and 2000, using the International Nuclear Event Scale". Journal of Radiological Protection 26 (1): 33. doi:10.1088/0952-4746/26/1/002. PMID 16522943. http://www.iop.org/EJ/abstract/0952-4746/26/1/002.
  5. ^ (AFP) – 10 août 2009. "AFP: Incident "significatif" à la centrale nucléaire de Gravelines, dans le Nord". Google.com. http://www.google.com/hostednews/afp/article/ALeqM5jDlQI2MpwzTvWT166NetwyFGPyiA. Retrieved 2010-09-13.
  6. ^ News | Slovenian Nuclear Safety Administration
  7. ^ http://200.0.198.11/comunicados/18_12_2006.pdf (Spanish)
  8. ^ http://www.jaea.go.jp/02/press2005/p06021301/index.html (Japanese)
  9. ^ http://www.aerb.gov.in/t/annrpt/2002/chapter8.pdf
  10. ^ a b NRC: SECY-01-0071 - Expanded NRC Participation in the Use of the International Nuclear Event Scale

External links

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