🕷️ Crawler Inspector

URL Lookup

Direct Parameter Lookup

Raw Queries and Responses

1. Shard Calculation

Query:

Response:

Calculated Shard: 62 (from laksa011)

2. Crawled Status Check

Query:

curl -X POST \
  'http://laksa062.int.ahrefs:8124/' \
  -H 'Content-Type: text/plain' \
  -H 'X-ClickHouse-Database: crawler3' \
  -H 'Authorization: Basic YXBpOg==' \
  -d 'SELECT getAhrefsURLFromUnparsed(src_unparsed) AS found_url, ifNull(toUnixTimestamp(download_stamp), 0) AS crawl_time, ifNull(toUnixTimestamp(props_url_first_seen), 0) AS first_indexed_time, download_http_code AS http_code, src_unparsed AS src_unparsed, src_root_hash AS src_root_hash, history_drop_reason AS history_drop_reason, meta_title AS meta_title, meta_descriptions AS meta_descriptions, attrs_boilerpipe_text AS attrs_boilerpipe_text, attrs_markdown AS attrs_markdown, attrs_readable_markdown AS attrs_readable_markdown, meta_canonical AS meta_canonical, ml_categories_json AS ml_categories_json, ml_types_json AS ml_types_json, ml_intent_types_json AS ml_intent_types_json, meta_language AS meta_language, attrs_author AS attrs_author, ifNull(toUnixTimestamp(attrs_publish_time), 0) AS attrs_publish_time, ifNull(toUnixTimestamp(attrs_original_publish_time), 0) AS attrs_original_publish_time, ifNull(attrs_is_republished, 0) AS attrs_is_republished, ifNull(attrs_nr_words, 0) AS attrs_nr_words, ifNull(attrs_boilerpipe_nr_words, 0) AS attrs_boilerpipe_nr_words, ifNull(body_ext_links_number, 0) AS body_ext_links_number, ifNull(body_int_links_number, 0) AS body_int_links_number, ifNull(meta_nofollow, 0) AS meta_nofollow, ifNull(meta_noarchive, 0) AS meta_noarchive, ifNull(props_was_rendered, 0) AS props_was_rendered, ifNull(src_redirect, \'\') AS src_redirect, ifNull(download_time_msec, 0) AS download_time_msec, ifNull(download_ttfb_msec, 0) AS download_ttfb_msec, ifNull(download_size, 0) AS download_size FROM crawler3.page_info_local FINAL PREWHERE (src_root_hash, src_unparsed) IN ((getAhrefsRootHashFromUnparsed(getAhrefsUnparsedNoserviceFromURL(\'https://www.britannica.com/event/Fukushima-accident\')), getAhrefsUnparsedNoserviceFromURL(\'https://www.britannica.com/event/Fukushima-accident\'))) FORMAT JSONEachRow'

Response:

{"found_url":"https:\/\/www.britannica.com\/event\/Fukushima-accident","crawl_time":1776312376,"first_indexed_time":1467655761,"http_code":200,"src_unparsed":"com,britannica!www,\/event\/Fukushima-accident s443","src_root_hash":"5455945239613777662","history_drop_reason":null,"meta_title":"Fukushima accident | Summary, Date, Effects, & Facts | Britannica","meta_descriptions":["Fukushima accident, disaster that occurred in 2011 at the Fukushima Daiichi (‘Number One’) nuclear power plant on the Pacific coast of northern Japan, which was caused by a severe earthquake and powerful series of tsunami waves and was the second worst nuclear power accident in history."],"attrs_boilerpipe_text":"Top Questions\nWhat was the Fukushima accident?\nHow did the Fukushima accident happen?\nWhat happened after the Fukushima accident?\nDid anyone die as a result of the Fukushima accident?\nFukushima accident\n,\naccident\nin 2011 at the Fukushima Daiichi (“Number One”)\nplant\nin northern\nJapan\n, the second worst nuclear accident (after the\nChernobyl disaster\nof 1986) in the history of\nnuclear power\ngeneration. The site is on Japan’s Pacific coast, in northeastern\nFukushima\nprefecture about 100 km (60 miles) south of\nSendai\n. The facility, operated by the\nTokyo Electric and Power Company (TEPCO), was made up of six boiling-water\nreactors\nconstructed between 1971 and 1979. At the time of the accident, only reactors 1–3 were operational, and reactor 4 served as temporary storage for spent fuel rods.\nWhat do you think?\nExplore the ProCon debate\nTEPCO officials reported that\ntsunami\nwaves generated by the main shock of the\nJapan earthquake on March 11, 2011\n, damaged the\nbackup\ngenerators at the Fukushima Daiichi plant. Although all three of the reactors that were operating were successfully shut down, the loss of power caused cooling systems to fail in each of them within the first few days of the\ndisaster\n. Rising residual\nheat\nwithin each reactor’s core caused the fuel rods in reactors 1, 2, and 3 to overheat and partially\nmelt down\n, leading at times to the release of\nradiation\n. Melted material fell to the bottom of the containment vessels in reactors 1 and 2 and bored sizable holes in the floor of each vessel—a fact that emerged in late May. Those holes partially exposed the nuclear material in the cores. Explosions resulting from the buildup of pressurized\nhydrogen\ngas occurred in the outer containment buildings enclosing reactors 1 and 3 on March 12 and March 14, respectively. Workers sought to cool and stabilize the three cores by pumping\nseawater\nand\nboric acid\ninto them. Because of concerns over possible radiation exposure, government officials established a 30-km (18-mile) no-fly zone around the facility, and a land area of 20-km (12.5-mile) radius around the plant—which covered nearly 600 square km (approximately 232 square miles)—was evacuated.\nA third explosion occurred on March 15 in the building surrounding reactor 2. At that time the explosion was thought to have damaged the containment\nvessel\nhousing the fuel rods. (In actuality, the explosion punched a second hole in the containment vessel; the first hole had been created earlier by melted nuclear material that passed through the bottom of the vessel.) In response, government officials designated a wider zone, extending to a radius of 30 km around the plant, within which residents were asked to remain indoors. The explosion, along with a fire touched off by rising temperatures in spent fuel rods stored in reactor 4, led to the release of higher levels of radiation from the plant.\nBritannica Quiz\nDisasters of Historic Proportion\nFukushima accident\nA man is checked for radiation exposure after having been evacuated from the quarantine area around a nuclear power station in Fukushima prefecture, Japan, that was damaged in the March 11, 2011, earthquake and tsunami.\nIn the days that followed, some 47,000 residents left their homes, many people in areas\nadjacent\nto the 20-km evacuation warning zone also prepared to leave, and workers at the plant made several attempts to cool the reactors using truck-mounted\nwater\ncannons and water dropped from\nhelicopters\n. Those efforts met with some success, which temporarily slowed the release of radiation; however, they were suspended several times after rising steam or smoke signaled an increased risk of radiation exposure.\nAs workers continued their attempts to cool the reactors, the appearance of increased levels of radiation in some local food and water supplies prompted Japanese and international officials to issue warnings about their\nconsumption\n. At the end of March, the evacuation zone was expanded to 30 km around the plant, and ocean water near the plant was discovered to have been contaminated with high levels of\niodine\n-131, which resulted from leakage of radioactive water through cracks in trenches and tunnels between the plant and the ocean. On April 6 plant officials announced that those cracks had been sealed, and later that month workers began to pump the irradiated water to an on-site storage building until it could be properly treated.\nOn April 12 nuclear regulators elevated the severity level of the nuclear emergency from 5 to 7—the highest level on the scale created by the\nInternational Atomic Energy Agency\n—placing it in the same category as the\nChernobyl accident\n, which had occurred in the\nSoviet Union\nin 1986. It was not until the middle of December 2011 that Japanese Prime Minister\nNoda Yoshihiko\ndeclared the facility stable, after the cold\nshutdown\nof the reactors was completed.\nAs the\nfallout\npattern became better understood, an additional corridor of land covering roughly 207 square km (80 square miles) and stretching away from the initial 20-km zone was also designated for evacuation in the months following the disaster. Months later,\nradiation\nlevels remained high in the evacuation zone, and government officials remarked that the area might be uninhabitable for decades. However, they also announced that radiation levels had declined enough in some towns located just beyond the original 20-km evacuation warning zone that residents could return to their homes there. Although many areas located within the 20-km evacuation warning zone and the expanded zone (an area called the “difficult-to-return” zone) continued to remain off-limits due to high radiation levels, officials began to allow limited activities (business activities and visitation but no lodging) in other previously evacuated areas with moderately high radiation levels. Beginning in July 2013, evacuation orders were lifted in some areas\ncharacterized\nby lower levels of radiation both within and beyond the 20-km evacuation warning zone. By March 2017 all evacuation orders in the areas outside the difficult-to-return zone (which continued to sequester some 371 square km [about 143 square miles]) had been lifted. A 2016 study on the effects of the accident on fish and marine products showed that the contamination level had decreased dramatically over time, though the\nradioactivity\nof some species, especially sedentary rockfish, remained elevated within the exclusion zone.\nQuick Facts\nAlso called:\nFukushima nuclear accident or Fukushima Daiichi nuclear accident\nDate:\n2011\nSmart, reliable knowledge for professionals, students, and curious minds everywhere.\nSUBSCRIBE\nA second, but smaller, nuclear accident took place in August 2013 when approximately 300 tonnes (330 tons) of irradiated\nwater\nused in ongoing cooling operations in reactors 1, 2, and 3 was\ndischarged\ninto the landscape surrounding the Fukushima Daiichi facility. TEPCO officials reported that the leak was the result of an open valve in the short barrier wall that surrounded several of the tanks used in radioactive water storage. The leak was severe enough to prompt Japan’s Nuclear Regulation Authority to classify it as a level-3 nuclear incident.","attrs_markdown":"[![Encyclopedia Britannica](https:\/\/cdn.britannica.com\/mendel\/eb-logo\/MendelNewThistleLogo.png)](https:\/\/www.britannica.com\/)\n\n[![Encyclopedia Britannica](https:\/\/cdn.britannica.com\/mendel\/eb-logo\/MendelNewThistleLogo.png)](https:\/\/www.britannica.com\/)\n\n[SUBSCRIBE](https:\/\/premium.britannica.com\/premium-membership\/?utm_source=premium&utm_medium=global-nav&utm_campaign=blue-evergreen)\n\n[SUBSCRIBE](https:\/\/premium.britannica.com\/premium-membership\/?utm_source=premium&utm_medium=global-nav-mobile&utm_campaign=blue-evergreen)\n\nLogin\n\nhttps:\/\/premium.britannica.com\/premium-membership\/?utm\\_source=premium\\&utm\\_medium=nav-login-box\\&utm\\_campaign=evergreen\n\n[SUBSCRIBE](https:\/\/premium.britannica.com\/premium-membership\/?utm_source=premium&utm_medium=hamburger-menu&utm_campaign=blue)\n\n- 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Questions](https:\/\/www.britannica.com\/event\/Fukushima-accident)   [References & Edit History](https:\/\/www.britannica.com\/event\/Fukushima-accident\/additional-info)  [Quick Facts & Related Topics](https:\/\/www.britannica.com\/facts\/Fukushima-accident)\n\n[Images](https:\/\/www.britannica.com\/event\/Fukushima-accident\/images-videos)\n\n[![damage at Fukushima Daiichi power plant](https:\/\/cdn.britannica.com\/93\/148893-004-179CD6F7\/Two-earthquake-containment-buildings-nuclear-power-plant-March-11-2011.jpg)](https:\/\/cdn.britannica.com\/93\/148893-050-26E0E6CE\/Two-earthquake-containment-buildings-nuclear-power-plant-March-11-2011.jpg)   [![Fukushima accident](https:\/\/cdn.britannica.com\/60\/148660-004-7B57F3CE\/safety-workers-evacuee-radiation-exposure-civilians-quarantine-March-11-2011.jpg)](https:\/\/cdn.britannica.com\/60\/148660-050-47FA35DE\/safety-workers-evacuee-radiation-exposure-civilians-quarantine-March-11-2011.jpg)   [![evacuation and exclusion zones of the Fukushima nuclear accident of 2011](https:\/\/cdn.britannica.com\/10\/196910-004-D30FB6FC\/Map-exclusion-zone-areas-evacuation-nuclear-power.jpg)](https:\/\/cdn.britannica.com\/10\/196910-050-108C6113\/Map-exclusion-zone-areas-evacuation-nuclear-power.jpg)\n\nAt a Glance\n\n[![damage at Fukushima Daiichi power plant](https:\/\/cdn.britannica.com\/93\/148893-050-26E0E6CE\/Two-earthquake-containment-buildings-nuclear-power-plant-March-11-2011.jpg?w=200&h=200&c=crop)](https:\/\/www.britannica.com\/summary\/Fukushima-accident)\n\n[Fukushima accident summary](https:\/\/www.britannica.com\/summary\/Fukushima-accident)\n\nQuizzes\n\n[![Warm water fuels Hurricane Katrina. This image depicts a 3-day average of actual dea surface temperatures for the Caribbean Sea and Atlantic Ocean, from August 25-27, 2005.](https:\/\/cdn.britannica.com\/49\/93649-131-FB06761E\/Satellite-image-sea-surface-temperatures-display-Hurricane-Aug-27-2005.jpg?w=200&h=200&c=crop)](https:\/\/www.britannica.com\/quiz\/disasters-of-historic-proportion)\n\n[Disasters of Historic Proportion](https:\/\/www.britannica.com\/quiz\/disasters-of-historic-proportion)\n\nRelated Questions\n\n- [How did the Fukushima accident happen?](https:\/\/www.britannica.com\/question\/How-did-the-Fukushima-accident-happen)\n- [What happened after the Fukushima accident?](https:\/\/www.britannica.com\/question\/What-happened-after-the-Fukushima-accident)\n- [Did anyone die as a result of the Fukushima accident?](https:\/\/www.britannica.com\/question\/Did-anyone-die-as-a-result-of-the-Fukushima-accident)\n- [Why did the Battle of Wake Island happen?](https:\/\/www.britannica.com\/question\/Why-did-the-Battle-of-Wake-Island-happen)\n- [What is the significance of the Battle of Wake Island?](https:\/\/www.britannica.com\/question\/What-is-the-significance-of-the-Battle-of-Wake-Island)\n\n![Britannica AI Icon](https:\/\/cdn.britannica.com\/mendel-resources\/3-179\/images\/chatbot\/star-ai.svg?v=3.179.9)\n\n[World History](https:\/\/www.britannica.com\/browse\/World-History)    [Accidents & Disasters](https:\/\/www.britannica.com\/browse\/Accidents-Disasters)\n\nCITE\n\n*verified*Cite\n\nWhile every effort has been made to follow citation style rules, there may be some discrepancies. Please refer to the appropriate style manual or other sources if you have any questions.\n\nSelect Citation Style\n\nCopy Citation\n\nShare\n\nShare\n\nShare to social media\n\n[Facebook](https:\/\/www.facebook.com\/BRITANNICA\/) [X](https:\/\/x.com\/britannica)\n\nURL\n\n<https:\/\/www.britannica.com\/event\/Fukushima-accident>\n\nFeedback\n\nExternal Websites\n\nFeedback\n\nThank you for your feedback\n\nOur editors will review what you’ve submitted and determine whether to revise the article.\n\nExternal Websites\n\n- [Digital Commons at University of South Florida - Lessons from Japan: Resilience after Tokyo and Fukushima](https:\/\/digitalcommons.usf.edu\/cgi\/viewcontent.cgi?article=1256&context=jss)\n- [NPR - Fukushima Daiichi Nuclear Disaster: 10 Years Later](https:\/\/www.npr.org\/transcripts\/991668971)\n- [United Nations Scientific Committee on the Effects of Atomic Radiation - Fukushima Daiichi Nuclear Power Station Accident](https:\/\/www.unscear.org\/unscear\/en\/areas-of-work\/fukushima.html)\n- [World Nuclear Association - Fukushima Daiichi Accident](https:\/\/world-nuclear.org\/information-library\/safety-and-security\/safety-of-plants\/fukushima-daiichi-accident)\n- [Energy Education - Fukushima nuclear accident](https:\/\/energyeducation.ca\/encyclopedia\/Fukushima_nuclear_accident)\n- [ABC listen - Late Night Live - Lessons of the Fukushima disaster](https:\/\/www.abc.net.au\/listen\/programs\/latenightlive\/legacy-of-fukushima-disaster\/13229294)\n- [International Atomic Energy Agency - Fukushima Daiichi Nuclear Accident](https:\/\/www.iaea.org\/topics\/response\/fukushima-daiichi-nuclear-accident)\n- [National Center for Biotechnology Information - Fukushima Daiichi Nuclear Accident](https:\/\/www.ncbi.nlm.nih.gov\/books\/NBK253938\/)\n- [BBC - Fukushima disaster: What happened at the nuclear plant?](https:\/\/www.bbc.com\/news\/world-asia-56252695)\n\n[![damage at Fukushima Daiichi power plant](https:\/\/cdn.britannica.com\/93\/148893-050-26E0E6CE\/Two-earthquake-containment-buildings-nuclear-power-plant-March-11-2011.jpg?w=400&h=300&c=crop)](https:\/\/cdn.britannica.com\/93\/148893-050-26E0E6CE\/Two-earthquake-containment-buildings-nuclear-power-plant-March-11-2011.jpg)\n\n[damage at Fukushima Daiichi power plant](https:\/\/cdn.britannica.com\/93\/148893-050-26E0E6CE\/Two-earthquake-containment-buildings-nuclear-power-plant-March-11-2011.jpg) Two of the damaged containment buildings at the Fukushima Daiichi nuclear power plant, northeastern Fukushima prefecture, Japan, several days after the March 11, 2011, earthquake and tsunami that crippled the installation.\n\n(more)\n\n# Fukushima accident\nJapan \\[2011\\]\n\nAsk Anything\n\nQuick Summary\n\nHomework Help\n\nAlso known as: Fukushima Daiichi nuclear accident, Fukushima nuclear accident[(Show More)](https:\/\/www.britannica.com\/event\/Fukushima-accident)\n\nWritten and fact-checked by\n\n[Britannica Editors Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree....](https:\/\/www.britannica.com\/editor\/The-Editors-of-Encyclopaedia-Britannica\/4419)\n\nBritannica Editors\n\nLast updated\n\nMar. 9, 2026\n\n•[History](https:\/\/www.britannica.com\/event\/Fukushima-accident\/additional-info#history)\n\n![Britannica AI Icon](https:\/\/cdn.britannica.com\/mendel-resources\/3-179\/images\/chatbot\/star-ai.svg?v=3.179.9) Britannica AI\n\nAsk Anything\n\nQuick Summary\n\nTable of Contents\n\nTable of Contents\n\nQuick Summary\n\nAsk Anything\n\nTop Questions\n\n### What was the Fukushima accident?\nThe Fukushima accident was an accident in 2011 at the Fukushima Daiichi (“Number One”) nuclear power plant in [Japan](https:\/\/www.britannica.com\/place\/Japan). It is the second worst nuclear accident in the history of [nuclear power](https:\/\/www.britannica.com\/technology\/nuclear-power) generation, behind the [Chernobyl disaster](https:\/\/www.britannica.com\/event\/Chernobyl-disaster).\n\n### How did the Fukushima accident happen?\nAn [earthquake and tsunami](https:\/\/www.britannica.com\/event\/Japan-earthquake-and-tsunami-of-2011) led to power loss in the Fukushima Daiichi plant. Without power, the cooling systems failed in three reactors, and their cores subsequently overheated. This led to a partial meltdown of the fuel rods, a fire in the storage reactor, explosions in the outer containment buildings (caused by a buildup of [hydrogen](https:\/\/www.britannica.com\/science\/hydrogen) gas), and the release of [radiation](https:\/\/www.britannica.com\/science\/radiation) into the air and ocean.\n\n### What happened after the Fukushima accident?\nImmediately after the Fukushima accident in 2011, [radiation](https:\/\/www.britannica.com\/science\/radiation) levels increased in food, water, and the ocean near the Fukushima Daiichi plant. Because of the threat of radiation exposure, some 150,000 people were forced to evacuate their homes. There were subsequently also multiple leaks at the facility. In 2013 one of these leaks was classified as a level-3 nuclear incident.\n\n### Did anyone die as a result of the Fukushima accident?\nNobody died as a direct result of the Fukushima nuclear disaster. However, in 2018 one worker in charge of measuring radiation at the plant died of [lung cancer](https:\/\/www.britannica.com\/science\/lung-cancer) caused by [radiation](https:\/\/www.britannica.com\/science\/radiation) exposure. In addition, there have been more than 2,000 disaster-related deaths. This classification includes deaths caused by suicide, stress, and interruption of medical care.\n\n**Fukushima accident**, [accident](https:\/\/www.britannica.com\/topic\/accident) in 2011 at the Fukushima Daiichi (“Number One”) [plant](https:\/\/www.britannica.com\/technology\/nuclear-power-plant) in northern [Japan](https:\/\/www.britannica.com\/place\/Japan), the second worst nuclear accident (after the [Chernobyl disaster](https:\/\/www.britannica.com\/event\/Chernobyl-disaster) of 1986) in the history of [nuclear power](https:\/\/www.britannica.com\/science\/nuclear-energy) generation. The site is on Japan’s Pacific coast, in northeastern [Fukushima](https:\/\/www.britannica.com\/place\/Fukushima-prefecture-Japan) prefecture about 100 km (60 miles) south of [Sendai](https:\/\/www.britannica.com\/place\/Sendai-Miyagi-prefecture-Japan). The facility, operated by the Tokyo Electric and Power Company (TEPCO), was made up of six boiling-water [reactors](https:\/\/www.britannica.com\/technology\/nuclear-reactor) constructed between 1971 and 1979. At the time of the accident, only reactors 1–3 were operational, and reactor 4 served as temporary storage for spent fuel rods.\n\n**What do you think?**\n\n- **[Is Nuclear Power a Good Form of Energy?](https:\/\/www.britannica.com\/procon\/nuclear-power-debate)**\n\n**Explore the ProCon debate**\n\nTEPCO officials reported that [tsunami](https:\/\/www.britannica.com\/science\/tsunami) waves generated by the main shock of the [Japan earthquake on March 11, 2011](https:\/\/www.britannica.com\/event\/Japan-earthquake-and-tsunami-of-2011), damaged the [backup](https:\/\/www.britannica.com\/dictionary\/backup) generators at the Fukushima Daiichi plant. Although all three of the reactors that were operating were successfully shut down, the loss of power caused cooling systems to fail in each of them within the first few days of the [disaster](https:\/\/www.britannica.com\/science\/disaster). Rising residual [heat](https:\/\/www.britannica.com\/science\/heat) within each reactor’s core caused the fuel rods in reactors 1, 2, and 3 to overheat and partially [melt down](https:\/\/www.britannica.com\/technology\/meltdown), leading at times to the release of [radiation](https:\/\/www.britannica.com\/science\/radiation). Melted material fell to the bottom of the containment vessels in reactors 1 and 2 and bored sizable holes in the floor of each vessel—a fact that emerged in late May. Those holes partially exposed the nuclear material in the cores. Explosions resulting from the buildup of pressurized [hydrogen](https:\/\/www.britannica.com\/science\/hydrogen) gas occurred in the outer containment buildings enclosing reactors 1 and 3 on March 12 and March 14, respectively. Workers sought to cool and stabilize the three cores by pumping [seawater](https:\/\/www.britannica.com\/science\/seawater) and [boric acid](https:\/\/www.britannica.com\/science\/boric-acid) into them. Because of concerns over possible radiation exposure, government officials established a 30-km (18-mile) no-fly zone around the facility, and a land area of 20-km (12.5-mile) radius around the plant—which covered nearly 600 square km (approximately 232 square miles)—was evacuated.\n\nA third explosion occurred on March 15 in the building surrounding reactor 2. At that time the explosion was thought to have damaged the containment [vessel](https:\/\/www.britannica.com\/dictionary\/vessel) housing the fuel rods. (In actuality, the explosion punched a second hole in the containment vessel; the first hole had been created earlier by melted nuclear material that passed through the bottom of the vessel.) In response, government officials designated a wider zone, extending to a radius of 30 km around the plant, within which residents were asked to remain indoors. The explosion, along with a fire touched off by rising temperatures in spent fuel rods stored in reactor 4, led to the release of higher levels of radiation from the plant.\n\n[![Warm water fuels Hurricane Katrina. This image depicts a 3-day average of actual dea surface temperatures for the Caribbean Sea and Atlantic Ocean, from August 25-27, 2005.](https:\/\/cdn.britannica.com\/49\/93649-131-FB06761E\/Satellite-image-sea-surface-temperatures-display-Hurricane-Aug-27-2005.jpg) Britannica Quiz Disasters of Historic Proportion](https:\/\/www.britannica.com\/quiz\/disasters-of-historic-proportion)\n\n[![Fukushima accident](https:\/\/cdn.britannica.com\/60\/148660-050-47FA35DE\/safety-workers-evacuee-radiation-exposure-civilians-quarantine-March-11-2011.jpg?w=300)](https:\/\/cdn.britannica.com\/60\/148660-050-47FA35DE\/safety-workers-evacuee-radiation-exposure-civilians-quarantine-March-11-2011.jpg)\n\n[Fukushima accident](https:\/\/cdn.britannica.com\/60\/148660-050-47FA35DE\/safety-workers-evacuee-radiation-exposure-civilians-quarantine-March-11-2011.jpg)A man is checked for radiation exposure after having been evacuated from the quarantine area around a nuclear power station in Fukushima prefecture, Japan, that was damaged in the March 11, 2011, earthquake and tsunami.\n\n(more)\n\nIn the days that followed, some 47,000 residents left their homes, many people in areas [adjacent](https:\/\/www.merriam-webster.com\/dictionary\/adjacent) to the 20-km evacuation warning zone also prepared to leave, and workers at the plant made several attempts to cool the reactors using truck-mounted [water](https:\/\/www.britannica.com\/science\/water) cannons and water dropped from [helicopters](https:\/\/www.britannica.com\/technology\/helicopter). Those efforts met with some success, which temporarily slowed the release of radiation; however, they were suspended several times after rising steam or smoke signaled an increased risk of radiation exposure.\n\nAs workers continued their attempts to cool the reactors, the appearance of increased levels of radiation in some local food and water supplies prompted Japanese and international officials to issue warnings about their [consumption](https:\/\/www.merriam-webster.com\/dictionary\/consumption). At the end of March, the evacuation zone was expanded to 30 km around the plant, and ocean water near the plant was discovered to have been contaminated with high levels of [iodine](https:\/\/www.britannica.com\/science\/iodine)\\-131, which resulted from leakage of radioactive water through cracks in trenches and tunnels between the plant and the ocean. On April 6 plant officials announced that those cracks had been sealed, and later that month workers began to pump the irradiated water to an on-site storage building until it could be properly treated.\n\nOn April 12 nuclear regulators elevated the severity level of the nuclear emergency from 5 to 7—the highest level on the scale created by the [International Atomic Energy Agency](https:\/\/www.britannica.com\/topic\/International-Atomic-Energy-Agency)—placing it in the same category as the [Chernobyl accident](https:\/\/www.britannica.com\/event\/Chernobyl-disaster), which had occurred in the [Soviet Union](https:\/\/www.britannica.com\/place\/Soviet-Union) in 1986. It was not until the middle of December 2011 that Japanese Prime Minister [Noda Yoshihiko](https:\/\/www.britannica.com\/biography\/Noda-Yoshihiko) declared the facility stable, after the cold [shutdown](https:\/\/www.britannica.com\/dictionary\/shutdown) of the reactors was completed.\n\n[![evacuation and exclusion zones of the Fukushima nuclear accident of 2011](https:\/\/cdn.britannica.com\/10\/196910-050-108C6113\/Map-exclusion-zone-areas-evacuation-nuclear-power.jpg)](https:\/\/cdn.britannica.com\/10\/196910-050-108C6113\/Map-exclusion-zone-areas-evacuation-nuclear-power.jpg)\n\n[evacuation and exclusion zones of the Fukushima nuclear accident of 2011](https:\/\/cdn.britannica.com\/10\/196910-050-108C6113\/Map-exclusion-zone-areas-evacuation-nuclear-power.jpg)\n\n(more)\n\nAs the [fallout](https:\/\/www.britannica.com\/science\/fallout-nuclear-physics) pattern became better understood, an additional corridor of land covering roughly 207 square km (80 square miles) and stretching away from the initial 20-km zone was also designated for evacuation in the months following the disaster. Months later, [radiation](https:\/\/www.britannica.com\/science\/radiation) levels remained high in the evacuation zone, and government officials remarked that the area might be uninhabitable for decades. However, they also announced that radiation levels had declined enough in some towns located just beyond the original 20-km evacuation warning zone that residents could return to their homes there. Although many areas located within the 20-km evacuation warning zone and the expanded zone (an area called the “difficult-to-return” zone) continued to remain off-limits due to high radiation levels, officials began to allow limited activities (business activities and visitation but no lodging) in other previously evacuated areas with moderately high radiation levels. Beginning in July 2013, evacuation orders were lifted in some areas [characterized](https:\/\/www.britannica.com\/dictionary\/characterized) by lower levels of radiation both within and beyond the 20-km evacuation warning zone. By March 2017 all evacuation orders in the areas outside the difficult-to-return zone (which continued to sequester some 371 square km \\[about 143 square miles\\]) had been lifted. A 2016 study on the effects of the accident on fish and marine products showed that the contamination level had decreased dramatically over time, though the [radioactivity](https:\/\/www.britannica.com\/science\/radioactivity) of some species, especially sedentary rockfish, remained elevated within the exclusion zone.\n\nQuick Facts\n\nAlso called:\n\nFukushima nuclear accident or Fukushima Daiichi nuclear accident\n\n*(Show more)*\n\nDate:\n\n2011\n\n*(Show more)*\n\nLocation:\n\n[Fukushima](https:\/\/www.britannica.com\/place\/Fukushima-prefecture-Japan)\n\n[Japan](https:\/\/www.britannica.com\/place\/Japan)\n\n[Miyagi](https:\/\/www.britannica.com\/place\/Miyagi)\n\n[Sendai](https:\/\/www.britannica.com\/place\/Sendai-Miyagi-prefecture-Japan)\n\n*(Show more)*\n\nContext:\n\n[Japan earthquake and tsunami of 2011](https:\/\/www.britannica.com\/event\/Japan-earthquake-and-tsunami-of-2011)\n\n*(Show more)*\n\n[See all related content](https:\/\/www.britannica.com\/facts\/Fukushima-accident)\n\nExplore Britannica Premium\\!\n\nSmart, reliable knowledge for professionals, students, and curious minds everywhere.\n\n[SUBSCRIBE](https:\/\/premium.britannica.com\/premium-membership\/?utm_source=premium&utm_medium=inline-cta&utm_campaign=smart-2026)\n\n![Penguin, ship, mountain, atlas](https:\/\/cdn.britannica.com\/marketing\/inline-left.webp)\n\n![shohei ohtani, plants, andy wharhol art](https:\/\/cdn.britannica.com\/marketing\/inline-right.webp)\n\n![Mobile](https:\/\/cdn.britannica.com\/marketing\/inline-mobile.webp?w=400)\n\nA second, but smaller, nuclear accident took place in August 2013 when approximately 300 tonnes (330 tons) of irradiated [water](https:\/\/www.britannica.com\/science\/water) used in ongoing cooling operations in reactors 1, 2, and 3 was [discharged](https:\/\/www.britannica.com\/dictionary\/discharged) into the landscape surrounding the Fukushima Daiichi facility. TEPCO officials reported that the leak was the result of an open valve in the short barrier wall that surrounded several of the tanks used in radioactive water storage. The leak was severe enough to prompt Japan’s Nuclear Regulation Authority to classify it as a level-3 nuclear incident.\n\n[The Editors of Encyclopaedia Britannica](https:\/\/www.britannica.com\/editor\/The-Editors-of-Encyclopaedia-Britannica\/4419) This article was most recently revised and updated by [Encyclopaedia Britannica](https:\/\/www.britannica.com\/contributor\/encyclopaedia-britannica\/12989892).","attrs_readable_markdown":"Top Questions\n\n### What was the Fukushima accident?\n### How did the Fukushima accident happen?\n### What happened after the Fukushima accident?\n### Did anyone die as a result of the Fukushima accident?\n\n**Fukushima accident**, [accident](https:\/\/www.britannica.com\/topic\/accident) in 2011 at the Fukushima Daiichi (“Number One”) [plant](https:\/\/www.britannica.com\/technology\/nuclear-power-plant) in northern [Japan](https:\/\/www.britannica.com\/place\/Japan), the second worst nuclear accident (after the [Chernobyl disaster](https:\/\/www.britannica.com\/event\/Chernobyl-disaster) of 1986) in the history of [nuclear power](https:\/\/www.britannica.com\/science\/nuclear-energy) generation. The site is on Japan’s Pacific coast, in northeastern [Fukushima](https:\/\/www.britannica.com\/place\/Fukushima-prefecture-Japan) prefecture about 100 km (60 miles) south of [Sendai](https:\/\/www.britannica.com\/place\/Sendai-Miyagi-prefecture-Japan). The facility, operated by the Tokyo Electric and Power Company (TEPCO), was made up of six boiling-water [reactors](https:\/\/www.britannica.com\/technology\/nuclear-reactor) constructed between 1971 and 1979. At the time of the accident, only reactors 1–3 were operational, and reactor 4 served as temporary storage for spent fuel rods.\n\n**What do you think?**\n\n**Explore the ProCon debate**\n\nTEPCO officials reported that [tsunami](https:\/\/www.britannica.com\/science\/tsunami) waves generated by the main shock of the [Japan earthquake on March 11, 2011](https:\/\/www.britannica.com\/event\/Japan-earthquake-and-tsunami-of-2011), damaged the [backup](https:\/\/www.britannica.com\/dictionary\/backup) generators at the Fukushima Daiichi plant. Although all three of the reactors that were operating were successfully shut down, the loss of power caused cooling systems to fail in each of them within the first few days of the [disaster](https:\/\/www.britannica.com\/science\/disaster). Rising residual [heat](https:\/\/www.britannica.com\/science\/heat) within each reactor’s core caused the fuel rods in reactors 1, 2, and 3 to overheat and partially [melt down](https:\/\/www.britannica.com\/technology\/meltdown), leading at times to the release of [radiation](https:\/\/www.britannica.com\/science\/radiation). Melted material fell to the bottom of the containment vessels in reactors 1 and 2 and bored sizable holes in the floor of each vessel—a fact that emerged in late May. Those holes partially exposed the nuclear material in the cores. Explosions resulting from the buildup of pressurized [hydrogen](https:\/\/www.britannica.com\/science\/hydrogen) gas occurred in the outer containment buildings enclosing reactors 1 and 3 on March 12 and March 14, respectively. Workers sought to cool and stabilize the three cores by pumping [seawater](https:\/\/www.britannica.com\/science\/seawater) and [boric acid](https:\/\/www.britannica.com\/science\/boric-acid) into them. Because of concerns over possible radiation exposure, government officials established a 30-km (18-mile) no-fly zone around the facility, and a land area of 20-km (12.5-mile) radius around the plant—which covered nearly 600 square km (approximately 232 square miles)—was evacuated.\n\nA third explosion occurred on March 15 in the building surrounding reactor 2. At that time the explosion was thought to have damaged the containment [vessel](https:\/\/www.britannica.com\/dictionary\/vessel) housing the fuel rods. (In actuality, the explosion punched a second hole in the containment vessel; the first hole had been created earlier by melted nuclear material that passed through the bottom of the vessel.) In response, government officials designated a wider zone, extending to a radius of 30 km around the plant, within which residents were asked to remain indoors. The explosion, along with a fire touched off by rising temperatures in spent fuel rods stored in reactor 4, led to the release of higher levels of radiation from the plant.\n\n[![Warm water fuels Hurricane Katrina. This image depicts a 3-day average of actual dea surface temperatures for the Caribbean Sea and Atlantic Ocean, from August 25-27, 2005.](https:\/\/cdn.britannica.com\/49\/93649-131-FB06761E\/Satellite-image-sea-surface-temperatures-display-Hurricane-Aug-27-2005.jpg) Britannica Quiz Disasters of Historic Proportion](https:\/\/www.britannica.com\/quiz\/disasters-of-historic-proportion)\n\n[Fukushima accident](https:\/\/cdn.britannica.com\/60\/148660-050-47FA35DE\/safety-workers-evacuee-radiation-exposure-civilians-quarantine-March-11-2011.jpg)A man is checked for radiation exposure after having been evacuated from the quarantine area around a nuclear power station in Fukushima prefecture, Japan, that was damaged in the March 11, 2011, earthquake and tsunami.\n\nIn the days that followed, some 47,000 residents left their homes, many people in areas [adjacent](https:\/\/www.merriam-webster.com\/dictionary\/adjacent) to the 20-km evacuation warning zone also prepared to leave, and workers at the plant made several attempts to cool the reactors using truck-mounted [water](https:\/\/www.britannica.com\/science\/water) cannons and water dropped from [helicopters](https:\/\/www.britannica.com\/technology\/helicopter). Those efforts met with some success, which temporarily slowed the release of radiation; however, they were suspended several times after rising steam or smoke signaled an increased risk of radiation exposure.\n\nAs workers continued their attempts to cool the reactors, the appearance of increased levels of radiation in some local food and water supplies prompted Japanese and international officials to issue warnings about their [consumption](https:\/\/www.merriam-webster.com\/dictionary\/consumption). At the end of March, the evacuation zone was expanded to 30 km around the plant, and ocean water near the plant was discovered to have been contaminated with high levels of [iodine](https:\/\/www.britannica.com\/science\/iodine)\\-131, which resulted from leakage of radioactive water through cracks in trenches and tunnels between the plant and the ocean. On April 6 plant officials announced that those cracks had been sealed, and later that month workers began to pump the irradiated water to an on-site storage building until it could be properly treated.\n\nOn April 12 nuclear regulators elevated the severity level of the nuclear emergency from 5 to 7—the highest level on the scale created by the [International Atomic Energy Agency](https:\/\/www.britannica.com\/topic\/International-Atomic-Energy-Agency)—placing it in the same category as the [Chernobyl accident](https:\/\/www.britannica.com\/event\/Chernobyl-disaster), which had occurred in the [Soviet Union](https:\/\/www.britannica.com\/place\/Soviet-Union) in 1986. It was not until the middle of December 2011 that Japanese Prime Minister [Noda Yoshihiko](https:\/\/www.britannica.com\/biography\/Noda-Yoshihiko) declared the facility stable, after the cold [shutdown](https:\/\/www.britannica.com\/dictionary\/shutdown) of the reactors was completed.\n\nAs the [fallout](https:\/\/www.britannica.com\/science\/fallout-nuclear-physics) pattern became better understood, an additional corridor of land covering roughly 207 square km (80 square miles) and stretching away from the initial 20-km zone was also designated for evacuation in the months following the disaster. Months later, [radiation](https:\/\/www.britannica.com\/science\/radiation) levels remained high in the evacuation zone, and government officials remarked that the area might be uninhabitable for decades. However, they also announced that radiation levels had declined enough in some towns located just beyond the original 20-km evacuation warning zone that residents could return to their homes there. Although many areas located within the 20-km evacuation warning zone and the expanded zone (an area called the “difficult-to-return” zone) continued to remain off-limits due to high radiation levels, officials began to allow limited activities (business activities and visitation but no lodging) in other previously evacuated areas with moderately high radiation levels. Beginning in July 2013, evacuation orders were lifted in some areas [characterized](https:\/\/www.britannica.com\/dictionary\/characterized) by lower levels of radiation both within and beyond the 20-km evacuation warning zone. By March 2017 all evacuation orders in the areas outside the difficult-to-return zone (which continued to sequester some 371 square km \\[about 143 square miles\\]) had been lifted. A 2016 study on the effects of the accident on fish and marine products showed that the contamination level had decreased dramatically over time, though the [radioactivity](https:\/\/www.britannica.com\/science\/radioactivity) of some species, especially sedentary rockfish, remained elevated within the exclusion zone.\n\nQuick Facts\n\nAlso called:\n\nFukushima nuclear accident or Fukushima Daiichi nuclear accident\n\nDate:\n\n2011\n\nSmart, reliable knowledge for professionals, students, and curious minds everywhere.\n\n[SUBSCRIBE](https:\/\/premium.britannica.com\/premium-membership\/?utm_source=premium&utm_medium=inline-cta&utm_campaign=smart-2026)\n\n![Penguin, ship, mountain, atlas](https:\/\/cdn.britannica.com\/marketing\/inline-left.webp)\n\n![shohei ohtani, plants, andy wharhol art](https:\/\/cdn.britannica.com\/marketing\/inline-right.webp)\n\n![Mobile](https:\/\/cdn.britannica.com\/marketing\/inline-mobile.webp?w=400)\n\nA second, but smaller, nuclear accident took place in August 2013 when approximately 300 tonnes (330 tons) of irradiated [water](https:\/\/www.britannica.com\/science\/water) used in ongoing cooling operations in reactors 1, 2, and 3 was [discharged](https:\/\/www.britannica.com\/dictionary\/discharged) into the landscape surrounding the Fukushima Daiichi facility. TEPCO officials reported that the leak was the result of an open valve in the short barrier wall that surrounded several of the tanks used in radioactive water storage. The leak was severe enough to prompt Japan’s Nuclear Regulation Authority to classify it as a level-3 nuclear incident.","meta_canonical":null,"ml_categories_json":"{\"\/Science\":698,\"\/Science\/Physics\":548,\"\/Reference\":135,\"\/News\":122,\"\/Reference\/General_Reference\":120}","ml_types_json":"{\"\/Article\":998,\"\/Article\/Definitions\":304}","ml_intent_types_json":"{\"Informational\":999}","meta_language":"en","attrs_author":null,"attrs_publish_time":1773014400,"attrs_original_publish_time":1467655761,"attrs_is_republished":1,"attrs_nr_words":"1993","attrs_boilerpipe_nr_words":"1147","body_ext_links_number":17,"body_int_links_number":97,"meta_nofollow":0,"meta_noarchive":0,"props_was_rendered":0,"src_redirect":"","download_time_msec":214,"download_ttfb_msec":207,"download_size":25585}

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Fukushima accident | Summary, Date, Effects, & Facts | Britannica

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Fukushima accident, disaster that occurred in 2011 at the Fukushima Daiichi (‘Number One’) nuclear power plant on the Pacific coast of northern Japan, which was caused by a severe earthquake and powerful series of tsunami waves and was the second worst nuclear power accident in history.

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Top Questions What was the Fukushima accident? How did the Fukushima accident happen? What happened after the Fukushima accident? Did anyone die as a result of the Fukushima accident? Fukushima accident , accident in 2011 at the Fukushima Daiichi (“Number One”) plant in northern Japan , the second worst nuclear accident (after the Chernobyl disaster of 1986) in the history of nuclear power generation. The site is on Japan’s Pacific coast, in northeastern Fukushima prefecture about 100 km (60 miles) south of Sendai . The facility, operated by the Tokyo Electric and Power Company (TEPCO), was made up of six boiling-water reactors constructed between 1971 and 1979. At the time of the accident, only reactors 1–3 were operational, and reactor 4 served as temporary storage for spent fuel rods. What do you think? Explore the ProCon debate TEPCO officials reported that tsunami waves generated by the main shock of the Japan earthquake on March 11, 2011 , damaged the backup generators at the Fukushima Daiichi plant. Although all three of the reactors that were operating were successfully shut down, the loss of power caused cooling systems to fail in each of them within the first few days of the disaster . Rising residual heat within each reactor’s core caused the fuel rods in reactors 1, 2, and 3 to overheat and partially melt down , leading at times to the release of radiation . Melted material fell to the bottom of the containment vessels in reactors 1 and 2 and bored sizable holes in the floor of each vessel—a fact that emerged in late May. Those holes partially exposed the nuclear material in the cores. Explosions resulting from the buildup of pressurized hydrogen gas occurred in the outer containment buildings enclosing reactors 1 and 3 on March 12 and March 14, respectively. Workers sought to cool and stabilize the three cores by pumping seawater and boric acid into them. Because of concerns over possible radiation exposure, government officials established a 30-km (18-mile) no-fly zone around the facility, and a land area of 20-km (12.5-mile) radius around the plant—which covered nearly 600 square km (approximately 232 square miles)—was evacuated. A third explosion occurred on March 15 in the building surrounding reactor 2. At that time the explosion was thought to have damaged the containment vessel housing the fuel rods. (In actuality, the explosion punched a second hole in the containment vessel; the first hole had been created earlier by melted nuclear material that passed through the bottom of the vessel.) In response, government officials designated a wider zone, extending to a radius of 30 km around the plant, within which residents were asked to remain indoors. The explosion, along with a fire touched off by rising temperatures in spent fuel rods stored in reactor 4, led to the release of higher levels of radiation from the plant. Britannica Quiz Disasters of Historic Proportion Fukushima accident A man is checked for radiation exposure after having been evacuated from the quarantine area around a nuclear power station in Fukushima prefecture, Japan, that was damaged in the March 11, 2011, earthquake and tsunami. In the days that followed, some 47,000 residents left their homes, many people in areas adjacent to the 20-km evacuation warning zone also prepared to leave, and workers at the plant made several attempts to cool the reactors using truck-mounted water cannons and water dropped from helicopters . Those efforts met with some success, which temporarily slowed the release of radiation; however, they were suspended several times after rising steam or smoke signaled an increased risk of radiation exposure. As workers continued their attempts to cool the reactors, the appearance of increased levels of radiation in some local food and water supplies prompted Japanese and international officials to issue warnings about their consumption . At the end of March, the evacuation zone was expanded to 30 km around the plant, and ocean water near the plant was discovered to have been contaminated with high levels of iodine -131, which resulted from leakage of radioactive water through cracks in trenches and tunnels between the plant and the ocean. On April 6 plant officials announced that those cracks had been sealed, and later that month workers began to pump the irradiated water to an on-site storage building until it could be properly treated. On April 12 nuclear regulators elevated the severity level of the nuclear emergency from 5 to 7—the highest level on the scale created by the International Atomic Energy Agency —placing it in the same category as the Chernobyl accident , which had occurred in the Soviet Union in 1986. It was not until the middle of December 2011 that Japanese Prime Minister Noda Yoshihiko declared the facility stable, after the cold shutdown of the reactors was completed. As the fallout pattern became better understood, an additional corridor of land covering roughly 207 square km (80 square miles) and stretching away from the initial 20-km zone was also designated for evacuation in the months following the disaster. Months later, radiation levels remained high in the evacuation zone, and government officials remarked that the area might be uninhabitable for decades. However, they also announced that radiation levels had declined enough in some towns located just beyond the original 20-km evacuation warning zone that residents could return to their homes there. Although many areas located within the 20-km evacuation warning zone and the expanded zone (an area called the “difficult-to-return” zone) continued to remain off-limits due to high radiation levels, officials began to allow limited activities (business activities and visitation but no lodging) in other previously evacuated areas with moderately high radiation levels. Beginning in July 2013, evacuation orders were lifted in some areas characterized by lower levels of radiation both within and beyond the 20-km evacuation warning zone. By March 2017 all evacuation orders in the areas outside the difficult-to-return zone (which continued to sequester some 371 square km [about 143 square miles]) had been lifted. A 2016 study on the effects of the accident on fish and marine products showed that the contamination level had decreased dramatically over time, though the radioactivity of some species, especially sedentary rockfish, remained elevated within the exclusion zone. Quick Facts Also called: Fukushima nuclear accident or Fukushima Daiichi nuclear accident Date: 2011 Smart, reliable knowledge for professionals, students, and curious minds everywhere. SUBSCRIBE A second, but smaller, nuclear accident took place in August 2013 when approximately 300 tonnes (330 tons) of irradiated water used in ongoing cooling operations in reactors 1, 2, and 3 was discharged into the landscape surrounding the Fukushima Daiichi facility. TEPCO officials reported that the leak was the result of an open valve in the short barrier wall that surrounded several of the tanks used in radioactive water storage. The leak was severe enough to prompt Japan’s Nuclear Regulation Authority to classify it as a level-3 nuclear incident.

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This image depicts a 3-day average of actual dea surface temperatures for the Caribbean Sea and Atlantic Ocean, from August 25-27, 2005.](https://cdn.britannica.com/49/93649-131-FB06761E/Satellite-image-sea-surface-temperatures-display-Hurricane-Aug-27-2005.jpg?w=200&h=200&c=crop)](https://www.britannica.com/quiz/disasters-of-historic-proportion) [Disasters of Historic Proportion](https://www.britannica.com/quiz/disasters-of-historic-proportion) Related Questions - [How did the Fukushima accident happen?](https://www.britannica.com/question/How-did-the-Fukushima-accident-happen) - [What happened after the Fukushima accident?](https://www.britannica.com/question/What-happened-after-the-Fukushima-accident) - [Did anyone die as a result of the Fukushima accident?](https://www.britannica.com/question/Did-anyone-die-as-a-result-of-the-Fukushima-accident) - [Why did the Battle of Wake Island happen?](https://www.britannica.com/question/Why-did-the-Battle-of-Wake-Island-happen) - [What is the significance of the Battle of Wake Island?](https://www.britannica.com/question/What-is-the-significance-of-the-Battle-of-Wake-Island) ![Britannica AI Icon](https://cdn.britannica.com/mendel-resources/3-179/images/chatbot/star-ai.svg?v=3.179.9) [World History](https://www.britannica.com/browse/World-History) [Accidents & Disasters](https://www.britannica.com/browse/Accidents-Disasters) CITE *verified*Cite While every effort has been made to follow citation style rules, there may be some discrepancies. 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External Websites - [Digital Commons at University of South Florida - Lessons from Japan: Resilience after Tokyo and Fukushima](https://digitalcommons.usf.edu/cgi/viewcontent.cgi?article=1256&context=jss) - [NPR - Fukushima Daiichi Nuclear Disaster: 10 Years Later](https://www.npr.org/transcripts/991668971) - [United Nations Scientific Committee on the Effects of Atomic Radiation - Fukushima Daiichi Nuclear Power Station Accident](https://www.unscear.org/unscear/en/areas-of-work/fukushima.html) - [World Nuclear Association - Fukushima Daiichi Accident](https://world-nuclear.org/information-library/safety-and-security/safety-of-plants/fukushima-daiichi-accident) - [Energy Education - Fukushima nuclear accident](https://energyeducation.ca/encyclopedia/Fukushima_nuclear_accident) - [ABC listen - Late Night Live - Lessons of the Fukushima disaster](https://www.abc.net.au/listen/programs/latenightlive/legacy-of-fukushima-disaster/13229294) - [International Atomic Energy Agency - Fukushima Daiichi Nuclear Accident](https://www.iaea.org/topics/response/fukushima-daiichi-nuclear-accident) - [National Center for Biotechnology Information - Fukushima Daiichi Nuclear Accident](https://www.ncbi.nlm.nih.gov/books/NBK253938/) - [BBC - Fukushima disaster: What happened at the nuclear plant?](https://www.bbc.com/news/world-asia-56252695) [![damage at Fukushima Daiichi power plant](https://cdn.britannica.com/93/148893-050-26E0E6CE/Two-earthquake-containment-buildings-nuclear-power-plant-March-11-2011.jpg?w=400&h=300&c=crop)](https://cdn.britannica.com/93/148893-050-26E0E6CE/Two-earthquake-containment-buildings-nuclear-power-plant-March-11-2011.jpg) [damage at Fukushima Daiichi power plant](https://cdn.britannica.com/93/148893-050-26E0E6CE/Two-earthquake-containment-buildings-nuclear-power-plant-March-11-2011.jpg) Two of the damaged containment buildings at the Fukushima Daiichi nuclear power plant, northeastern Fukushima prefecture, Japan, several days after the March 11, 2011, earthquake and tsunami that crippled the installation. (more) # Fukushima accident Japan \[2011\] Ask Anything Quick Summary Homework Help Also known as: Fukushima Daiichi nuclear accident, Fukushima nuclear accident[(Show More)](https://www.britannica.com/event/Fukushima-accident) Written and fact-checked by [Britannica Editors Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree....](https://www.britannica.com/editor/The-Editors-of-Encyclopaedia-Britannica/4419) Britannica Editors Last updated Mar. 9, 2026 •[History](https://www.britannica.com/event/Fukushima-accident/additional-info#history) ![Britannica AI Icon](https://cdn.britannica.com/mendel-resources/3-179/images/chatbot/star-ai.svg?v=3.179.9) Britannica AI Ask Anything Quick Summary Table of Contents Table of Contents Quick Summary Ask Anything Top Questions ### What was the Fukushima accident? The Fukushima accident was an accident in 2011 at the Fukushima Daiichi (“Number One”) nuclear power plant in [Japan](https://www.britannica.com/place/Japan). It is the second worst nuclear accident in the history of [nuclear power](https://www.britannica.com/technology/nuclear-power) generation, behind the [Chernobyl disaster](https://www.britannica.com/event/Chernobyl-disaster). ### How did the Fukushima accident happen? An [earthquake and tsunami](https://www.britannica.com/event/Japan-earthquake-and-tsunami-of-2011) led to power loss in the Fukushima Daiichi plant. Without power, the cooling systems failed in three reactors, and their cores subsequently overheated. This led to a partial meltdown of the fuel rods, a fire in the storage reactor, explosions in the outer containment buildings (caused by a buildup of [hydrogen](https://www.britannica.com/science/hydrogen) gas), and the release of [radiation](https://www.britannica.com/science/radiation) into the air and ocean. ### What happened after the Fukushima accident? Immediately after the Fukushima accident in 2011, [radiation](https://www.britannica.com/science/radiation) levels increased in food, water, and the ocean near the Fukushima Daiichi plant. Because of the threat of radiation exposure, some 150,000 people were forced to evacuate their homes. There were subsequently also multiple leaks at the facility. In 2013 one of these leaks was classified as a level-3 nuclear incident. ### Did anyone die as a result of the Fukushima accident? Nobody died as a direct result of the Fukushima nuclear disaster. However, in 2018 one worker in charge of measuring radiation at the plant died of [lung cancer](https://www.britannica.com/science/lung-cancer) caused by [radiation](https://www.britannica.com/science/radiation) exposure. In addition, there have been more than 2,000 disaster-related deaths. This classification includes deaths caused by suicide, stress, and interruption of medical care. **Fukushima accident**, [accident](https://www.britannica.com/topic/accident) in 2011 at the Fukushima Daiichi (“Number One”) [plant](https://www.britannica.com/technology/nuclear-power-plant) in northern [Japan](https://www.britannica.com/place/Japan), the second worst nuclear accident (after the [Chernobyl disaster](https://www.britannica.com/event/Chernobyl-disaster) of 1986) in the history of [nuclear power](https://www.britannica.com/science/nuclear-energy) generation. The site is on Japan’s Pacific coast, in northeastern [Fukushima](https://www.britannica.com/place/Fukushima-prefecture-Japan) prefecture about 100 km (60 miles) south of [Sendai](https://www.britannica.com/place/Sendai-Miyagi-prefecture-Japan). The facility, operated by the Tokyo Electric and Power Company (TEPCO), was made up of six boiling-water [reactors](https://www.britannica.com/technology/nuclear-reactor) constructed between 1971 and 1979. At the time of the accident, only reactors 1–3 were operational, and reactor 4 served as temporary storage for spent fuel rods. **What do you think?** - **[Is Nuclear Power a Good Form of Energy?](https://www.britannica.com/procon/nuclear-power-debate)** **Explore the ProCon debate** TEPCO officials reported that [tsunami](https://www.britannica.com/science/tsunami) waves generated by the main shock of the [Japan earthquake on March 11, 2011](https://www.britannica.com/event/Japan-earthquake-and-tsunami-of-2011), damaged the [backup](https://www.britannica.com/dictionary/backup) generators at the Fukushima Daiichi plant. Although all three of the reactors that were operating were successfully shut down, the loss of power caused cooling systems to fail in each of them within the first few days of the [disaster](https://www.britannica.com/science/disaster). Rising residual [heat](https://www.britannica.com/science/heat) within each reactor’s core caused the fuel rods in reactors 1, 2, and 3 to overheat and partially [melt down](https://www.britannica.com/technology/meltdown), leading at times to the release of [radiation](https://www.britannica.com/science/radiation). Melted material fell to the bottom of the containment vessels in reactors 1 and 2 and bored sizable holes in the floor of each vessel—a fact that emerged in late May. Those holes partially exposed the nuclear material in the cores. Explosions resulting from the buildup of pressurized [hydrogen](https://www.britannica.com/science/hydrogen) gas occurred in the outer containment buildings enclosing reactors 1 and 3 on March 12 and March 14, respectively. Workers sought to cool and stabilize the three cores by pumping [seawater](https://www.britannica.com/science/seawater) and [boric acid](https://www.britannica.com/science/boric-acid) into them. Because of concerns over possible radiation exposure, government officials established a 30-km (18-mile) no-fly zone around the facility, and a land area of 20-km (12.5-mile) radius around the plant—which covered nearly 600 square km (approximately 232 square miles)—was evacuated. A third explosion occurred on March 15 in the building surrounding reactor 2. At that time the explosion was thought to have damaged the containment [vessel](https://www.britannica.com/dictionary/vessel) housing the fuel rods. (In actuality, the explosion punched a second hole in the containment vessel; the first hole had been created earlier by melted nuclear material that passed through the bottom of the vessel.) In response, government officials designated a wider zone, extending to a radius of 30 km around the plant, within which residents were asked to remain indoors. The explosion, along with a fire touched off by rising temperatures in spent fuel rods stored in reactor 4, led to the release of higher levels of radiation from the plant. [![Warm water fuels Hurricane Katrina. This image depicts a 3-day average of actual dea surface temperatures for the Caribbean Sea and Atlantic Ocean, from August 25-27, 2005.](https://cdn.britannica.com/49/93649-131-FB06761E/Satellite-image-sea-surface-temperatures-display-Hurricane-Aug-27-2005.jpg) Britannica Quiz Disasters of Historic Proportion](https://www.britannica.com/quiz/disasters-of-historic-proportion) [![Fukushima accident](https://cdn.britannica.com/60/148660-050-47FA35DE/safety-workers-evacuee-radiation-exposure-civilians-quarantine-March-11-2011.jpg?w=300)](https://cdn.britannica.com/60/148660-050-47FA35DE/safety-workers-evacuee-radiation-exposure-civilians-quarantine-March-11-2011.jpg) [Fukushima accident](https://cdn.britannica.com/60/148660-050-47FA35DE/safety-workers-evacuee-radiation-exposure-civilians-quarantine-March-11-2011.jpg)A man is checked for radiation exposure after having been evacuated from the quarantine area around a nuclear power station in Fukushima prefecture, Japan, that was damaged in the March 11, 2011, earthquake and tsunami. (more) In the days that followed, some 47,000 residents left their homes, many people in areas [adjacent](https://www.merriam-webster.com/dictionary/adjacent) to the 20-km evacuation warning zone also prepared to leave, and workers at the plant made several attempts to cool the reactors using truck-mounted [water](https://www.britannica.com/science/water) cannons and water dropped from [helicopters](https://www.britannica.com/technology/helicopter). Those efforts met with some success, which temporarily slowed the release of radiation; however, they were suspended several times after rising steam or smoke signaled an increased risk of radiation exposure. As workers continued their attempts to cool the reactors, the appearance of increased levels of radiation in some local food and water supplies prompted Japanese and international officials to issue warnings about their [consumption](https://www.merriam-webster.com/dictionary/consumption). At the end of March, the evacuation zone was expanded to 30 km around the plant, and ocean water near the plant was discovered to have been contaminated with high levels of [iodine](https://www.britannica.com/science/iodine)\-131, which resulted from leakage of radioactive water through cracks in trenches and tunnels between the plant and the ocean. On April 6 plant officials announced that those cracks had been sealed, and later that month workers began to pump the irradiated water to an on-site storage building until it could be properly treated. On April 12 nuclear regulators elevated the severity level of the nuclear emergency from 5 to 7—the highest level on the scale created by the [International Atomic Energy Agency](https://www.britannica.com/topic/International-Atomic-Energy-Agency)—placing it in the same category as the [Chernobyl accident](https://www.britannica.com/event/Chernobyl-disaster), which had occurred in the [Soviet Union](https://www.britannica.com/place/Soviet-Union) in 1986. It was not until the middle of December 2011 that Japanese Prime Minister [Noda Yoshihiko](https://www.britannica.com/biography/Noda-Yoshihiko) declared the facility stable, after the cold [shutdown](https://www.britannica.com/dictionary/shutdown) of the reactors was completed. [![evacuation and exclusion zones of the Fukushima nuclear accident of 2011](https://cdn.britannica.com/10/196910-050-108C6113/Map-exclusion-zone-areas-evacuation-nuclear-power.jpg)](https://cdn.britannica.com/10/196910-050-108C6113/Map-exclusion-zone-areas-evacuation-nuclear-power.jpg) [evacuation and exclusion zones of the Fukushima nuclear accident of 2011](https://cdn.britannica.com/10/196910-050-108C6113/Map-exclusion-zone-areas-evacuation-nuclear-power.jpg) (more) As the [fallout](https://www.britannica.com/science/fallout-nuclear-physics) pattern became better understood, an additional corridor of land covering roughly 207 square km (80 square miles) and stretching away from the initial 20-km zone was also designated for evacuation in the months following the disaster. Months later, [radiation](https://www.britannica.com/science/radiation) levels remained high in the evacuation zone, and government officials remarked that the area might be uninhabitable for decades. However, they also announced that radiation levels had declined enough in some towns located just beyond the original 20-km evacuation warning zone that residents could return to their homes there. Although many areas located within the 20-km evacuation warning zone and the expanded zone (an area called the “difficult-to-return” zone) continued to remain off-limits due to high radiation levels, officials began to allow limited activities (business activities and visitation but no lodging) in other previously evacuated areas with moderately high radiation levels. Beginning in July 2013, evacuation orders were lifted in some areas [characterized](https://www.britannica.com/dictionary/characterized) by lower levels of radiation both within and beyond the 20-km evacuation warning zone. By March 2017 all evacuation orders in the areas outside the difficult-to-return zone (which continued to sequester some 371 square km \[about 143 square miles\]) had been lifted. A 2016 study on the effects of the accident on fish and marine products showed that the contamination level had decreased dramatically over time, though the [radioactivity](https://www.britannica.com/science/radioactivity) of some species, especially sedentary rockfish, remained elevated within the exclusion zone. Quick Facts Also called: Fukushima nuclear accident or Fukushima Daiichi nuclear accident *(Show more)* Date: 2011 *(Show more)* Location: [Fukushima](https://www.britannica.com/place/Fukushima-prefecture-Japan) [Japan](https://www.britannica.com/place/Japan) [Miyagi](https://www.britannica.com/place/Miyagi) [Sendai](https://www.britannica.com/place/Sendai-Miyagi-prefecture-Japan) *(Show more)* Context: [Japan earthquake and tsunami of 2011](https://www.britannica.com/event/Japan-earthquake-and-tsunami-of-2011) *(Show more)* [See all related content](https://www.britannica.com/facts/Fukushima-accident) Explore Britannica Premium\! Smart, reliable knowledge for professionals, students, and curious minds everywhere. [SUBSCRIBE](https://premium.britannica.com/premium-membership/?utm_source=premium&utm_medium=inline-cta&utm_campaign=smart-2026) ![Penguin, ship, mountain, atlas](https://cdn.britannica.com/marketing/inline-left.webp) ![shohei ohtani, plants, andy wharhol art](https://cdn.britannica.com/marketing/inline-right.webp) ![Mobile](https://cdn.britannica.com/marketing/inline-mobile.webp?w=400) A second, but smaller, nuclear accident took place in August 2013 when approximately 300 tonnes (330 tons) of irradiated [water](https://www.britannica.com/science/water) used in ongoing cooling operations in reactors 1, 2, and 3 was [discharged](https://www.britannica.com/dictionary/discharged) into the landscape surrounding the Fukushima Daiichi facility. TEPCO officials reported that the leak was the result of an open valve in the short barrier wall that surrounded several of the tanks used in radioactive water storage. The leak was severe enough to prompt Japan’s Nuclear Regulation Authority to classify it as a level-3 nuclear incident. [The Editors of Encyclopaedia Britannica](https://www.britannica.com/editor/The-Editors-of-Encyclopaedia-Britannica/4419) This article was most recently revised and updated by [Encyclopaedia Britannica](https://www.britannica.com/contributor/encyclopaedia-britannica/12989892).

Readable Markdown

Top Questions ### What was the Fukushima accident? ### How did the Fukushima accident happen? ### What happened after the Fukushima accident? ### Did anyone die as a result of the Fukushima accident? **Fukushima accident**, [accident](https://www.britannica.com/topic/accident) in 2011 at the Fukushima Daiichi (“Number One”) [plant](https://www.britannica.com/technology/nuclear-power-plant) in northern [Japan](https://www.britannica.com/place/Japan), the second worst nuclear accident (after the [Chernobyl disaster](https://www.britannica.com/event/Chernobyl-disaster) of 1986) in the history of [nuclear power](https://www.britannica.com/science/nuclear-energy) generation. The site is on Japan’s Pacific coast, in northeastern [Fukushima](https://www.britannica.com/place/Fukushima-prefecture-Japan) prefecture about 100 km (60 miles) south of [Sendai](https://www.britannica.com/place/Sendai-Miyagi-prefecture-Japan). The facility, operated by the Tokyo Electric and Power Company (TEPCO), was made up of six boiling-water [reactors](https://www.britannica.com/technology/nuclear-reactor) constructed between 1971 and 1979. At the time of the accident, only reactors 1–3 were operational, and reactor 4 served as temporary storage for spent fuel rods. **What do you think?** **Explore the ProCon debate** TEPCO officials reported that [tsunami](https://www.britannica.com/science/tsunami) waves generated by the main shock of the [Japan earthquake on March 11, 2011](https://www.britannica.com/event/Japan-earthquake-and-tsunami-of-2011), damaged the [backup](https://www.britannica.com/dictionary/backup) generators at the Fukushima Daiichi plant. Although all three of the reactors that were operating were successfully shut down, the loss of power caused cooling systems to fail in each of them within the first few days of the [disaster](https://www.britannica.com/science/disaster). Rising residual [heat](https://www.britannica.com/science/heat) within each reactor’s core caused the fuel rods in reactors 1, 2, and 3 to overheat and partially [melt down](https://www.britannica.com/technology/meltdown), leading at times to the release of [radiation](https://www.britannica.com/science/radiation). Melted material fell to the bottom of the containment vessels in reactors 1 and 2 and bored sizable holes in the floor of each vessel—a fact that emerged in late May. Those holes partially exposed the nuclear material in the cores. Explosions resulting from the buildup of pressurized [hydrogen](https://www.britannica.com/science/hydrogen) gas occurred in the outer containment buildings enclosing reactors 1 and 3 on March 12 and March 14, respectively. Workers sought to cool and stabilize the three cores by pumping [seawater](https://www.britannica.com/science/seawater) and [boric acid](https://www.britannica.com/science/boric-acid) into them. Because of concerns over possible radiation exposure, government officials established a 30-km (18-mile) no-fly zone around the facility, and a land area of 20-km (12.5-mile) radius around the plant—which covered nearly 600 square km (approximately 232 square miles)—was evacuated. A third explosion occurred on March 15 in the building surrounding reactor 2. At that time the explosion was thought to have damaged the containment [vessel](https://www.britannica.com/dictionary/vessel) housing the fuel rods. (In actuality, the explosion punched a second hole in the containment vessel; the first hole had been created earlier by melted nuclear material that passed through the bottom of the vessel.) In response, government officials designated a wider zone, extending to a radius of 30 km around the plant, within which residents were asked to remain indoors. The explosion, along with a fire touched off by rising temperatures in spent fuel rods stored in reactor 4, led to the release of higher levels of radiation from the plant. [![Warm water fuels Hurricane Katrina. This image depicts a 3-day average of actual dea surface temperatures for the Caribbean Sea and Atlantic Ocean, from August 25-27, 2005.](https://cdn.britannica.com/49/93649-131-FB06761E/Satellite-image-sea-surface-temperatures-display-Hurricane-Aug-27-2005.jpg) Britannica Quiz Disasters of Historic Proportion](https://www.britannica.com/quiz/disasters-of-historic-proportion) [Fukushima accident](https://cdn.britannica.com/60/148660-050-47FA35DE/safety-workers-evacuee-radiation-exposure-civilians-quarantine-March-11-2011.jpg)A man is checked for radiation exposure after having been evacuated from the quarantine area around a nuclear power station in Fukushima prefecture, Japan, that was damaged in the March 11, 2011, earthquake and tsunami. In the days that followed, some 47,000 residents left their homes, many people in areas [adjacent](https://www.merriam-webster.com/dictionary/adjacent) to the 20-km evacuation warning zone also prepared to leave, and workers at the plant made several attempts to cool the reactors using truck-mounted [water](https://www.britannica.com/science/water) cannons and water dropped from [helicopters](https://www.britannica.com/technology/helicopter). Those efforts met with some success, which temporarily slowed the release of radiation; however, they were suspended several times after rising steam or smoke signaled an increased risk of radiation exposure. As workers continued their attempts to cool the reactors, the appearance of increased levels of radiation in some local food and water supplies prompted Japanese and international officials to issue warnings about their [consumption](https://www.merriam-webster.com/dictionary/consumption). At the end of March, the evacuation zone was expanded to 30 km around the plant, and ocean water near the plant was discovered to have been contaminated with high levels of [iodine](https://www.britannica.com/science/iodine)\-131, which resulted from leakage of radioactive water through cracks in trenches and tunnels between the plant and the ocean. On April 6 plant officials announced that those cracks had been sealed, and later that month workers began to pump the irradiated water to an on-site storage building until it could be properly treated. On April 12 nuclear regulators elevated the severity level of the nuclear emergency from 5 to 7—the highest level on the scale created by the [International Atomic Energy Agency](https://www.britannica.com/topic/International-Atomic-Energy-Agency)—placing it in the same category as the [Chernobyl accident](https://www.britannica.com/event/Chernobyl-disaster), which had occurred in the [Soviet Union](https://www.britannica.com/place/Soviet-Union) in 1986. It was not until the middle of December 2011 that Japanese Prime Minister [Noda Yoshihiko](https://www.britannica.com/biography/Noda-Yoshihiko) declared the facility stable, after the cold [shutdown](https://www.britannica.com/dictionary/shutdown) of the reactors was completed. As the [fallout](https://www.britannica.com/science/fallout-nuclear-physics) pattern became better understood, an additional corridor of land covering roughly 207 square km (80 square miles) and stretching away from the initial 20-km zone was also designated for evacuation in the months following the disaster. Months later, [radiation](https://www.britannica.com/science/radiation) levels remained high in the evacuation zone, and government officials remarked that the area might be uninhabitable for decades. However, they also announced that radiation levels had declined enough in some towns located just beyond the original 20-km evacuation warning zone that residents could return to their homes there. Although many areas located within the 20-km evacuation warning zone and the expanded zone (an area called the “difficult-to-return” zone) continued to remain off-limits due to high radiation levels, officials began to allow limited activities (business activities and visitation but no lodging) in other previously evacuated areas with moderately high radiation levels. Beginning in July 2013, evacuation orders were lifted in some areas [characterized](https://www.britannica.com/dictionary/characterized) by lower levels of radiation both within and beyond the 20-km evacuation warning zone. By March 2017 all evacuation orders in the areas outside the difficult-to-return zone (which continued to sequester some 371 square km \[about 143 square miles\]) had been lifted. A 2016 study on the effects of the accident on fish and marine products showed that the contamination level had decreased dramatically over time, though the [radioactivity](https://www.britannica.com/science/radioactivity) of some species, especially sedentary rockfish, remained elevated within the exclusion zone. Quick Facts Also called: Fukushima nuclear accident or Fukushima Daiichi nuclear accident Date: 2011 Smart, reliable knowledge for professionals, students, and curious minds everywhere. [SUBSCRIBE](https://premium.britannica.com/premium-membership/?utm_source=premium&utm_medium=inline-cta&utm_campaign=smart-2026) ![Penguin, ship, mountain, atlas](https://cdn.britannica.com/marketing/inline-left.webp) ![shohei ohtani, plants, andy wharhol art](https://cdn.britannica.com/marketing/inline-right.webp) ![Mobile](https://cdn.britannica.com/marketing/inline-mobile.webp?w=400) A second, but smaller, nuclear accident took place in August 2013 when approximately 300 tonnes (330 tons) of irradiated [water](https://www.britannica.com/science/water) used in ongoing cooling operations in reactors 1, 2, and 3 was [discharged](https://www.britannica.com/dictionary/discharged) into the landscape surrounding the Fukushima Daiichi facility. TEPCO officials reported that the leak was the result of an open valve in the short barrier wall that surrounded several of the tanks used in radioactive water storage. The leak was severe enough to prompt Japan’s Nuclear Regulation Authority to classify it as a level-3 nuclear incident.

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