Cooling failure directly after the earthquake
After the March 11, 2011 earthquake, Nuclear Engineering International reported that units 1, 2 and 3 were automatically shut down. Units 4, 5 and 6 had already been shut down for maintenance.[13] Major electrical supply failures in the region meant that electric power on site and in particular for the cooling system was only available from the plant itself. After main generation stopped, power supply for cooling was transferred to emergency diesel generators. However, the generators installed to provide backup power for the cooling systems for units 1–3 were damaged by the tsunami;[14] they started up correctly but stopped abruptly about 1 hour later.[15] In Japan a nuclear emergency is declared when a plant experiences cooling problems, so a nuclear emergency was declared when the diesel generators stopped and cooling was interrupted. Cooling is needed to remove residual reactor heat even when a plant has been shut down. Batteries, which last about eight hours, were used to power the reactor controls and valves during the electrical outage.[16][17][18] Japanese ground forces were said to be trucking generators and batteries to the site.[19]
An evacuation order was issued to people living within 3 kilometres (1.9 mi) of the plant, affecting approximately 5,800 residents, but others living less than 10 kilometres (6.2 mi) from the power plant were advised to stay indoors.[20] Later the evacuation was expanded to a 10 kilometres (6.2 mi) radius, and then to 20 kilometres (12 mi).[21][22][23]
[edit] Explosion and collapse of secondary structure of unit 1
On March 12, 2011, after midnight JST, it was reported that the Tokyo Electric Power Company was considering venting hot gas from number 1 reactor vessel into the atmosphere, which could result in the release of radiation.[24] The Tokyo Electric Company reported that radiation levels were rising in the turbine building for reactor 1.[25] At 2:00 JST, the pressure inside the reactor containment was reported to be 600 kPa (6 bar or 87 psi), 200 kPa (2 bar or 29 psi) higher than under normal conditions.[15] At 5:30 JST the pressure inside Reactor 1 was reported to be 2.1 times the "design capacity",[26] 820 kPa (8.2 bar or 120 psi).[27] At 6:10 JST, the IAEA reported that unit 2 was also experiencing cooling problems.[28]
Potentially radioactive steam was released from the primary circuit into the secondary containment area to reduce mounting pressure.[29] On March 12, 2011, at 6:40 JST, Chief Cabinet Secretary Yukio Edano stated that the amount of potential radiation would be small and that the prevailing winds are blowing out to sea.[30] Radiation levels recorded by the plant control room were reported to be approximately 0.07 mSv per hour.[31] Radiation levels measured at a monitoring post near the plant's main gate were reported to be more than eight times above normal.[32][33] In a press release at 7 am JST March 12, TEPCO stated, "Measurement of radioactive material (iodine, etc.) by monitoring car indicates increasing value compared to normal level. One of the monitoring posts is also indicating higher than normal level."[23] At 13:30 JST, radioactive caesium-137 was detected near reactor 1, which indicates that the core of the reactor may be leaking radiation.[34][35][36] At 15:29 JST (06:43 GMT) TEPCO reported that radiation levels at the site boundary exceeded the regulatory limits.[37] An announcement of TEPCO indicated that the gamma ray radiation recorded on the main gate was increased from 69 nanogray/hour (nGy/h) (4:00 JST, 12 March) to 866 nGy/h 40 minutes later and reached the peak of 385.5 microgray/hour (1 μGy = 1000 nGy) at 10:30 am JST.[38] Fuel rods may have been exposed to the air.[39]
The Prime Minister of Japan, Naoto Kan, visited the plant for a briefing on March 12, 2011.[40] The Tokyo fire department sent a special nuclear rescue team to Fukushima.[41]
Over 50,000 people were evacuated during March 12th.[42]
Wikinews has related news: Explosion at earthquake-damaged Fukushima nuclear power plant
At 15:36 JST (7:36 GMT) on March 12, there was an explosion at the plant injuring four workers.[43] The explosion was officially confirmed at 18:43 JST (9:43 GMT).[10] According to a Reuters report of 21:36 JST (7:36 ET), Chief Cabinet Secretary Yukio Edano indicated that the building housing the No. 1 reactor containment vessel had collapsed as a result of a hydrogen explosion.[44] Hydrogen had been produced due to falling water levels in the reactor and leaked from the pressure vessel into the containment building.[44] At 19:37 JST (10:37 GMT) Reuters reported that Mr Ian Hore-Lacy, communications director at the World Nuclear Association, had suggested the same cause.[45] Edano further indicated that the container of the reactor had remained intact and there had been no large leaks of radioactive material.[44][11] An increase in radiation levels was confirmed following the explosion.[46][47] According to the Fukushima prefectural government, the hourly radiation from the plant reached 1.015 mSv (0.1015 rem), an amount equivalent to that allowable for ordinary people in one year."[48][49] Two independent nuclear experts cited design differences between the Chernobyl Nuclear Power Plant and the Fukushima I Nuclear Power Plant,[50][51] one of them saying he did not believe that a Chernobyl-style disaster will occur.[50]
At 21:00 JST (12:00 GMT) TEPCO announced that they planned to cool the leaking reactor with sea water (which started at 20:20 JST), then using boric acid to act as a neutron absorber to prevent a criticality accident.[52][53] The sea water would take five to ten hours to fill the reactor core, after which it would require seawater cooling for around ten days.[44] At 23:00 JST (14:00 GMT) TEPCO announced that due to the quake at 22:15[54] the filling of the reactor with sea water and boric acid had been temporarily stopped but has been resumed after a short while.[55][56]
At 01:17 JST on Sunday 13th March (16:17 GMT), the Japan Atomic Energy Agency announced that it was rating the Fukushima accident at 4 (accident with local consequences) on the 0–7 International Nuclear Event Scale (INES), below the Three Mile Island accident in seriousness.[57]
[edit] Threat of meltdown at unit 1
In a press conference, a speaker of the Japanese nuclear authorities was translated to English as having said that a nuclear meltdown was happening and that a pipe had burst at unit 1. However, the Japanese prime minister soon denied that a nuclear meltdown was happening and emphasized that the containment of unit 1 was still intact. At around 17:00 CET, Japanese authorities measured a strong increase on iodine and cesium at the unit, suspecting a partial meltdown to be the cause.[58][59] The Japanese newspaper Asahi Shimbun reported that cooling water had lowered so much that less than half of the length of the nuclear fuel rods was still covered. Japanese authorities said that pressure inside the unit was still high, but the temperature was dropping.[60]
[edit] Cooling problems at unit 3
Early on March 13, an official of the Japan Nuclear and Industrial Safety Agency told a news conference that the emergency cooling system of Reactor 3 had failed, spurring an urgent search for a means to supply cooling water to the reactor vessel in order to prevent a meltdown of the No. 3 reactor core.[61]
At 7:30 JST TEPCO was preparing to release radioactive steam, indicating that "the amount of radiation to be released would be small and not of a level that would affect human health".[62]
[edit] Effect on employees and residents
The Guardian reported at 17:35 JST (8:35 GMT) on March 12 that NHK advised residents of the Fukushima area "to stay inside, close doors and windows and turn off air conditioning. They were also advised to cover their mouths with masks, towels or handkerchiefs" as well as not to drink tap water.[63] At 19:07 JST (10:07 GMT) Reuters reported that the exclusion zone had been extended to 20 kilometres (12 mi) around the plant.[64][65] BBC correspondent Nick Ravenscroft was stopped 60 kilometres (37 mi) from the plant by police.[66] Air traffic has been restricted in a 20 kilometres (12 mi) radius around the plant, according to a NOTAM.[67] The BBC has reported as of 22:49 JST (13:49 GMT) "A team from the National Institute of Radiological Sciences has been despatched to Fukushima as a precaution, reports NHK. It was reportedly made up of doctors, nurses and other individuals with expertise in dealing with radiation exposure, and had been taken by helicopter to a base 5 km from the nuclear plant."[10]
"More than 300,000 people have now been evacuated from homes in northern Japan and that number will rise as the government increases the exclusion zone around the Fukushima nuclear power plant."[10] At 23:43 JST (14:43 GMT) BBC News stated that the four workers that were injured in the blast at the Fukushima No. 1 nuclear plant were conscious and their injuries were not life-threatening.[10] This was followed at 23:59 JST (14:59 GMT) with BBC advising both Kyodo and NHK reporting at least three residents evacuated from a town near quake-hit Fukushima No. 1 plant have been exposed to radiation.[10] According to the World Nuclear Association, a worker operating in a crane on the exhaust stack had died.[11] According to TEPCO this worker had died at Fukushima Daini.[12]
At 22:53 JST (13:53 GMT) Tokyo Broadcasting System (TBS), quoting Fukushima representatives, has reported that there was an evacuation of 30 staff members and 60 patients due to the explosion. From those evacuees three patients received a checkup for radiation exposure by the hospital staff at Futaba, a town 3.5 miles from the power plant. One out of three people who received the checkup showed an exposure of "100,000 counts per minute" (about 45 nCi) while the other two people showed exposure of 40,000 (≈18 nCi) and 30,000 (≈14 nCi) counts per minute. According to experts, this is a level of radiation from which an individual needs to be decontaminated. While all three patients were decontaminated, about 90 other evacuees may also require decontamination.[68]
... salu na stranu, u svetu ima oko 450 potencijalnih "kandidata" za katastrofu, a u samom japanu preko 50 nuklearnih elektrana :exploder: .
