Fukushima Nuclear Accident Update Log
Updates of 25 March 2011
- Story Resources
- In Focus: Fukushima Nuclear Accident
- Fukushima Nuclear Accident: Information Sheet
- Criteria for Use in Preparedness and Response for a Nuclear or Radiological Emergency
- International Nuclear and Radiological Event Scale (INES)
- IAEA Incident and Emergency Centre (IEC)
- International Seismic Safety Centre (ISSC)
- Response Assistance Network (RANET)
- Japan Nuclear and Industrial Safety Agency (NISA)
On Friday, 25 March 2011, Graham Andrew, Special Adviser to the IAEA Director General on Scientific and Technical Affairs, provided the following information on the current status of nuclear safety in Japan.
1. Current Situation
There has not been much change at the Fukushima Daiichi plant over the last 24 hours. Some positive trends are continuing, but there remain areas of uncertainty that are of serious concern.
Unit 1 is with offsite AC power to the lighting of its central control room and to some of its instrumentation. Unit 3 now also has lighting to its central control room, but not power to its instrumentation. It remains too early to evaluate how much instrumentation may effectively be recovered at Units 1, 2, 3 and 4.
Reactor pressure is decreasing at Unit 1 and so is seawater injection. On the other hand, pressure readings in the reactor pressure vessels remain unreliable in Unit 2 and have become unreliable in Unit 3.
The temperature at the feed-water nozzle of the reactor pressure vessel continues to decrease (to 205 °C) at Unit 1, and at Unit 3 (42.8 °C), and it remains stable at Unit 2 (105 °C).
The dose rates in the containment vessel and suppression chamber have continued to decrease at Unit 1, and remained stable at Unit 2.
At Unit 3, radiation exposure of three TEPCO subcontracting workers has been confirmed. They were working in the basement, with contaminated water on the floor. Two of them were transferred to hospital with contamination of their feet.
There are no significant developments to report at Unit 4, where water spraying continues.
Units 5 and 6 remain in comparatively good condition. Temperatures at both, which had risen when the cooling pumps were briefly shut down in order to switch to off-site power, temperatures have since been restored to lower levels, and both units are still in cold shutdown. For the same reasons, a brief rise in temperature also occurred at the Common Spent Fuel Pool on 24 March.
2. Radiation Monitoring
On-site radiation monitoring at the Daiichi NPP indicates that dose rates continue to decrease.
Deposition of radioactivity is monitored daily by Japanese authorities in all 47 prefectures. From 23 March to 24 March, additional deposition has been detected in 7 of the 47 prefectures. Considerable variations are observed, the deposition at this day ranged from 42 to 16 000 Becquerel per square metre for iodine-131; the highest value determined for caesium-137 was 210 Becquerel per square metre. For the Shinjuku district of Tokyo, the deposition of iodine-131 on this day increased by 13 000 Becquerel per square metre, and the caesium-137 deposition by 160 Becquerel per square metre.
As far as the marine environment is concerned, sampling of air and seawater continues to be carried out by the Japanese Ministry of Education, Culture, Sport, Science and Technology (MEXT). Results are sent to the IAEA Monaco laboratory for assessment.
Measurements in the marine environment have been carried out 30 km off-shore and 330 metres from the discharge points on 23 March and repeated the next day. The results made available up to 25 March indicate concentrations of iodine-31 (some 80 becquerel/litre) and caesium-137 (about 26 becquerel/litre). This contamination is most likely due to atmospheric fallout rather than just ocean currents. Dilution in the ocean is expected to decrease rapidly this initial surface contamination. Caesium-137 will be more important over the long term owing to its half-life (30 years) compared to that of iodine-131 (8 days). Modelling of the dispersion of these radionuclides has been started, and the first results are becoming available. Marine dispersion will of course be much slower than atmospheric transport.
Since yesterday, additional data has been made available by the Japanese authorities concerning radionuclide concentrations in milk, vegetables and drinking water.
Levels of iodine-131 exceeded levels recommended by the Japanese authorities in five raw milk samples taken in Fukushima Prefecture, and exceeded levels of iodine-131 and cesium-137 in one vegetable (mizuna) sampled in Ibaraki Prefecture.
Monitoring of drinking water is on-going, iodine-131 in drinking water was detected in 13 prefectures, caesium-137 was detected in 6 of the 47 prefectures. During the period of 19 to 23 March, all results remained below the limits set by the Japanese government. However, permissible levels of iodine-131 were exceeded in drinking water samples taken in the Fukushima and Ibaraki Prefectures and in Tokyo from 17 to 23 March. More positively, the iodine-131 levels in drinking water for Tokyo are now below limits for consumption for infants recommended by the Japanese authorities and restrictions have been lifted.
As a result of food monitoring where contamination exceeded the levels recommended by the Japanese authorities, current restrictions on the distribution of milk are in place in 2 prefectures (Fukushima, Ibaraki) and on the distribution of certain vegetables in 4 prefectures (Fukushima, Ibaraki, Tochigi, Gunma). This regulatory approach is to prevent food contaminated with radioactivity above these limits entering the market and thereby, ensure the safety of foods. On 23 March, the Japanese authorities requested sampling of agricultural products in 6 neighbouring prefectures (Miyagi, Yamagata, Saitama, Chiba, Niigata and Nagano). This request for further food monitoring covers the same types of foods currently under restriction.
The joint FAO/IAEA food safety mission is currently travelling to Japan.
On 25 March, the IAEA radiation monitoring team made additional measurements at distances from 34 to 62 km from the Fukushima nuclear power plant. At these locations, the dose rate ranged from 0.73 to 8.8 microsievert per hour. At the same locations, results of beta-gamma contamination measurements ranged from 0.07 to 0.96 Megabecquerel per square metre.
Director General Amano had a video conference today with the UN Secretary General and the Heads of a number of other UN system organizations concerning the accident. In addition, close coordination led by the IAEA through the Joint Radiation Emergency Management Plan of International Organizations (JPLAN) continues.
Fukushima Nuclear Accident Update (25 March 2011, 15:45 UTC)
Japanese authorities have informed the IAEA that on 24 March, examinations of the thyroid glands in 66 children (14 of which are infants) were conducted near the evacuation area around the Fukushima nuclear plant. The exams were conducted at the Kawamata Town Health Center (40-50 kilometres from Fukushima Daiichi NPP) and Kawamata Town Yamakiya Branch Office (30-40 kilometres from Fukushima Daiichi NPP).
According to a 25 March 2011 Nuclear and Industrial Safety Agency press release, the results of the examinations indicated that the dose rate "of all the 66 children including 14 infants from 1 to 6 years old had no big difference from the level of background and was at the level of no problem in light of the view of Nuclear Safety Commission."
Regarding developments at the Fukushima Daiichi nuclear power plant, "white smoke" was reported at Units 1, 2 and 4 from 21:20 UTC on 24 March. Sea water injection to Units 1, 2, 3 and 4 continues as of 23:00 UTC 24 March.
The IAEA is seeking further information on the latest status of all Units and spent nuclear fuel at Fukushima Daiichi NPP.
Fukushima Nuclear Accident Update (25 March 2011, 05.15 UTC)
Update on Conditions of Fukushima Daiichi Nuclear Power Plant
At Unit 1 workers have advanced the restoration of off-site electricity and lighting in the Unit's main control room was recovered as of 24 March, 11:30 UTC. They are now checking the availability of the cooling system.
While the pressure in the reactor vessel remains high, Japanese authorities are reporting that it has stabilized.
At Unit 2 engineers are working for the recovery of lighting in the main control room, and the instrumentation and cooling systems.
At Unit 3, around 120 tonnes of seawater was injected in the spent fuel pool via the cooling and purification line. The operation was carried out between 23 March, 20:35 UTC and 24 March, 07:05 UTC.
Work was under way for the recovery of the instruments and cooling systems. However, it had to be suspended because three workers were exposed to elevated levels of radiation on 24 March.
At Unit 4, the spent fuel pool was sprayed with around 150 tonnes of water using concrete pump truck. The operation was carried out between 24 March, 05:36 UTC and 06:30 UTC of the same day.
At Units 5 and 6, repair of the temporary pump for Residual Heat Removal (RHR) was completed as of 24 March, 07:14 UTC, and cooling started again 21 minutes later.
At the Common Spent Fuel, the power supply was restored as of 24 March, 06:37 UTC and cooling started again 28 minutes later. Work is now under way for the recovery of the lighting and instrumentation systems.
As of 24 March, 09:40 UTC, the water temperature of the pool was around 73 °C.
As of 24 March, 10:30 UTC workers continue to inject seawater into the reactor pressure vessels of Units 1, 2 and 3 and are preparing to inject pure water.
Fukushima Nuclear Accident Update (25 March 2011, 02.50 UTC)
As previously reported, three workers at the Fukushima Daiichi nuclear power plant were exposed on 24 March to elevated levels of radiation. The IAEA has received additional information on the incident from the Japanese authorities.
The three were contracted workers laying cables in the turbine building of the Unit 3 reactor. Two of them were found to have radioactivity on their feet and legs.
These were washed in the attempt to remove radioactivity, but since there was a possibility of Beta-ray burning of the skin, the two were taken to the Fukushima University Hospital for examination and then transferred to Japan's National Institute of Radiological Sciences for further examination. They are expected to be monitored for around four days.
It is thought that the workers ignored their dosimeters' alarm believing it to be to be false and continued working with their feet in contaminated water.
The Nuclear and Industrial Safety Agency (NISA) of Japan instructed TEPCO to review the radiation control system immediately in order to avoid similar incidents in the future.
As of 24 March, 19:30 Japan time, the number of workers at the Fukushima Daiichi nuclear power plant found to have received more than 100 millisieverts of radiation dose totalled 17 including the three contract workers. The remaining fourteen are TEPCO's employees.