Tsunami: Hvordan Opstår De Dødbringende Kæmpebølger? (Kan 2024)
Fukushima Nuclear Emergency.
Af betydelig bekymring efter det største chok og tsunamien var status for flere atomkraftværker i Tohoku-regionen. Reaktorerne ved de tre kernekraftværker tættest på jordskælvets episenter blev automatisk lukket ned efter jordskælvet. Denne proces skærer også hovedkraften til disse anlæg og deres kølesystemer. Den efterfølgende oversvømmelse af tsunamibølgerne beskadigede backupgeneratorerne på nogle af disse anlæg, især ved Fukushima Daiichi (“nummer et”), der drives af Tokyo Electric Power Co. (TEPCO). Fukushima Daiichi, der består af seks kogende vandreaktorer konstrueret mellem 1971 og 1979, lå langs Stillehavskysten i det nordøstlige Fukushima præfektur omkring 100 km (60 mi) syd for Sendai. På ulykkestidspunktet var det kun reaktorer 1-3, der var i drift,og reaktor 4 tjente som midlertidig opbevaring af brugt brændstofstænger.
Da strømmen var gået, mislykkedes kølesystemerne i tre reaktorer inden for de første dage af katastrofen, og deres kerner blev derefter overophedet, hvilket førte til delvis nedbrydning af brændstofstængerne. (Nogle plantearbejdere tilskrev dog mindst en delvis nedsmeltning til kølervæskesprængninger forårsaget af jordskælvets jordvibrationer.) Smeltet materiale faldt væk fra stængerne og landede på bunden af indeslutningsbeholdere i reaktorer 1 og 2 og brændte betydelige huller i gulvet i hvert fartøj. Disse huller udsatte delvis det nukleare materiale i kernerne. Eksplosioner, der er resultatet af opbygningen af brændstof under tryk i de ydre indeslutningsbygninger, der omslutter reaktorer 1, 2 og 3, sammen med en ild, der er berørt af stigende temperaturer i de brugte brændstofstænger placeret i reaktor 4,førte til frigivelse af betydelige niveauer af stråling fra anlægget i dagene og ugerne efter jordskælvet. Arbejderne søgte at afkøle og stabilisere de beskadigede reaktorer ved at pumpe havvand og borsyre i dem.
Because of concerns over possible radiation exposure, Japanese officials established a 30-km (18-mi) no-fly zone around the facility, and an area of 20 km (12.5 mi) around the plant was evacuated. The evacuation zone was later expanded to coincide with the borders of the 30-km no-fly radius. Within this 10-km (6.2-mi) outer ring, residents were asked to either leave or remain indoors. The appearance of increased levels of radiation in some local food and water supplies prompted officials in Japan and overseas to issue warnings about their consumption. At the end of March, seawater near the Daiichi facility was discovered to have been contaminated with high levels of radioactive iodine-131. The contamination stemmed from the exposure of pumped-in seawater to radiation inside the facility; this water later leaked into the ocean through cracks in water-filled trenches and tunnels located between the facility and the ocean. On April 6, plant officials announced that the 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.
In mid-April Japanese nuclear regulators elevated the severity level of the nuclear emergency at the Fukushima Daiichi facility from 5 to 7—the highest level on the scale created by the International Atomic Energy Agency—placing the Fukushima accident in the same category as the Chernobyl accident, which occurred in the Soviet Union in 1986. At year’s end, 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 in five towns located just beyond the original 20-km evacuation zone to levels low enough that residents would be allowed to return to their homes. Japanese Prime Minister Yoshihiko Noda declared the facility stable after the cold shutdown of the reactors was completed on December 16.
Relief Efforts.
In the first hours after the earthquake, then Japanese Prime Minister Naoto Kan moved to set up an emergency command centre in Tokyo, and a large number of rescue workers and some 100,000 members of the Japanese Self-Defense Force were rapidly mobilized to deal with the crisis. In addition, the Japanese government requested that U.S. military personnel stationed in the country be available to help in relief efforts, and a U.S. Navy aircraft carrier was dispatched to the area. Several countries, including Australia, China, India, New Zealand, South Korea, and the United States, sent search-and-rescue teams, and dozens of other countries and major international relief organizations, such as the Red Cross and Red Crescent, pledged financial and material support to Japan. In addition, a large number of private and nongovernmental organizations within Japan and worldwide soon established relief funds to aid victims and assist with rescue and recovery efforts.
The rescue work itself was hampered initially by the difficulty in getting personnel and supplies to the devastation zone; compounding the difficulty were periods of inclement weather that curtailed air operations. Workers in the disaster zones then faced widespread seas of destruction: vast areas, even whole towns and cities, had been washed away or covered by great piles of mud and debris. Although some people were rescued from the rubble in the first several days following the main shock and tsunami, most of the relief work involved the recovery of bodies, including hundreds that began washing ashore in several areas after having been swept out to sea.
In the immediate aftermath of the disaster, several hundred thousand people were in shelters, often with limited or negligible supplies of food or water, and tens of thousands more remained stranded and isolated in the worst-hit areas as rescuers worked to reach them. Within days the number of displaced people in the Fukushima area grew as the situation with the nuclear reactors on the coast deteriorated and people left the quarantined area. Gradually many people were able to find other places to stay in the Tohoku area, or they relocated to other parts of the country; some quarter million people were still in hundreds of shelters in the region two weeks after the quake, but by the end of the year, that number had been reduced by more than two-thirds. Tens of thousands of these displaced residents were living in some 50,000 prefabricated temporary housing units that had been set up in Sendai and other tsunami-damaged locations.
In the weeks following the disaster, much of northern Honshu’s transportation and services infrastructure was at least partially restored, and repairs continued until train lines and major highways were again fully operational. The region’s power supply continued to be affected, however, by the ongoing situation at the Fukushima plant, resulting in temporary power outages and rolling blackouts. The loss of businesses and factories from earthquake and tsunami damage, as well as the uncertainties surrounding the power supply, severely reduced the region’s postdisaster manufacturing output. Industries most affected included those producing semiconductors and other high-technology items and automobiles.
