Fukushima Nuclear Accident Update Log
Updates of 31 March 2011
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- 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)
→ Summary of Reactor Status
On Thursday, 31 March 2011, the IAEA provided the following information on the current status of nuclear safety in Japan:
1. Current Situation
Overall at the Fukushima Daiichi plant, the situation remains very serious.
The Unit 1 condenser is full. Pumping water from the Unit-1 turbine building basement to the Unit 1 condenser has been stopped as of 22:30 UTC on 28 March. For Units 2 and 3, in order to prepare for removal of the water from the turbine building basement, pumping of water from the condenser to the suppression pool water surge tank started at 07:45 UTC, 29 March and 08:40 UTC, March 28 respectively.
For Unit 1 fresh water has been continuously injected into the Reactor Pressure Vessel (RPV) through the feed-water line at an indicated flow rate of 8 m3/h using a temporary electric pump with diesel backup. In Unit 2 fresh water is injected continuously through the fire extinguisher line at an indicated rate of 8 m3/h using a temporary electric pump with diesel backup. In Unit 3 fresh water is being injected continuously at about 7 m3/h into the reactor core through the fire extinguisher line using a temporary electric pump with diesel backup.
The indicated temperature at the feed water nozzle of the RPV on Unit 1 has decreased from 281 °C to 251 °C and at the bottom of RPV decreased from 134 °C to 128 °C. There appears to be a corresponding decrease in RPV pressure with a slight decrease in Drywell pressure. The indicated temperature at the feed water nozzle of the RPV of Unit 2 has increased from 177 °C to 181 °C. The temperature at the bottom of RPV was not reported. Indicated Drywell pressure remains at atmospheric pressure. The indicated temperature at the feed water nozzle of the RPV in Unit 3 is about 89 °C and at the bottom of RPV is about 114 °C. The validity of the RPV temperature measurement at the feed water nozzle is still under investigation.
No further information is available regarding the plan to commence the pumping of water into the Unit 1 Spent Fuel Pool by concrete pumping truck from 29 March. On Unit 2 the temporary electric pump supplying water to the spent fuel pool experienced a malfunction. Spent fuel pool water supply was changed to a fire truck pump but a crack was discovered in a hose on 30 March 04:10 UTC. Pumping water to the spent fuel pool was therefore stopped. Pumping was subsequently restored and water was fed into spent fuel pool in Unit 2 from 10:05 UTC on March 30. Water injection into the spent fuel pool in Unit 4 by concrete pump was completed at 09:33 UTC on March 30.
Units 5 and 6 remain in cold shutdown
2. Radiation Monitoring
On 30 March, deposition of iodine-131 was detected in 8 prefectures, and deposition of cesium-137 in 12 prefectures. On 30 March in the prefectures where deposition of iodine-131 was reported, the range was from 2.5 to 240 becquerel per square metre. For caesium-137, the range was from 3 to 57 becquerel per square metre. In the Shinjyuku district of Tokyo, the daily deposition of both iodine-131 and cesium-137 on 30 March was below 30 becquerel per square metre. No significant changes were reported in the 45 prefectures in gamma dose rates compared to yesterday.
Most of the previously imposed recommendations for restrictions on drinking have been lifted. As of 28 March, recommendations for restrictions based on I-131 concentration remain in place in four villages of in the Fukushima prefecture, in three of these villages, restrictions continue to apply for infants only.
Two IAEA teams are currently monitoring radiation levels and radioactivity in the environment in Japan. On 30 March, one team made gamma dose-rate measurements in the Tokyo region at 7 locations. Gamma-dose rates measured ranged from 0.03 to 0.28 microsievert per hour, which is within or slightly above the background. The second team made additional measurements at 7 locations in the Hirono area, South of Fukushima-Daiichi NPP. The measurement locations were at distances of 23 to 39 km from the Fukushima nuclear power plant. The dose rates ranged from 0.5 to 4.9 microsievert per hour. At the same locations, results of beta-gamma contamination measurements ranged from 0.04 to 0.34 Megabecquerel per square metre.
Since our briefing of yesterday, significant data related to food contamination has been submitted by the Japanese Ministry of Health, Labour and Welfare. Seventy-six samples were taken from 28 - 30 March, and reported on 30 March. Analytical results for 51 of the 76 samples for various vegetables, fruit (strawberries), seafood (sardines) and unprocessed raw milk in eight prefectures (Chiba, Fukushima, Gunma, Ibaraki, Kanagawa, Niigata, Saitama and Yamagata), indicated that iodine-131, caesium-134 and caesium-137 were either not detected or were below the regulation values set by the Japanese authorities. However, it was reported that analytical results in Fukushima prefecture for the remaining 25 of the 76 samples for broccoli, cabbage, rapeseed, spinach and other leafy vegetables, indicated that iodine-131 and/or caesium-134 and caesium-137 exceeded the regulation values set by the Japanese authorities.
The Joint FAO/IAEA Food Safety Assessment Team met with local government officials in Gunma prefecture on Wednesday. Farmers and producers were also represented and the meeting attracted media coverage. The questions to the IAEA/FAO team mainly focused on technical issues of remediation strategies, including the implications of long term releases if the NPP is not stabilized, the disposal of contaminated produce, mechanisms of 131I and 137Cs contamination, other possible radionuclides that may be produced/should be monitored, contamination of fruit and mushrooms, occupational exposure risks in the handling animals and agricultural products, feeding strategies for animals in affected areas, monitoring of soil and fallout and remediation strategies and methodologies. There were also discussions with producers and farmer organizations over the development of strategies for the next cropping season.
Local government officials briefed the FAO/IAEA Team on current knowledge of the extent of contamination in Gunma prefecture, including the principal agricultural products affected and levels of contamination found.
The Joint FAO/IAEA Team presented their report and responded to inquires at a follow-up inter-ministerial meeting in Tokyo. The meeting was attended by representatives of the Japanese Cabinet Office, Ministry of Foreign Affairs, Ministry of Health, Labour and Welfare and the Ministry of Agriculture. Strong interest was expressed as to the remediation of the agricultural land, continued possible contamination of agricultural products, and the need to maintain communication with relevant ministries in the future.
New results from the marine monitoring stations 30 km off-shore were reported for 28 March. These results indicate a decrease for the northernmost sampling station for I-131 and a slight increase for Cs-137 as compared to values measured on 27 March. For sampling points situated towards the south of the transect an increase has been recorded, both for I-131 and for Cs-137 as compared to the previous day, with maximum concentrations in water below 30 Bq/l and 20 Bq/l respectively, still considerably lower than the maxima recorded on 23 March. This increase can be correlated with trends in concentrations measured close to the discharge points.
The latest analyses in seawater 330 m south of the discharge point of NPP Units 1 - 4, and 30 m north of the discharge point of Units 5 - 6 were made available for 29 March. In particular readings of 130 000 Bq/l of I-131, 32 000 Bq/l of Cs-137 and 31 000 Bq/l of Cs-134 were reported near Units 1 - 4.
The Russian Federation, Ireland and Switzerland reported the detection of very small amounts of iodine-131 and cesium-137 in air. Highest levels found are in the order of a few millibecquerel per cubic meter. The levels are not of any radiological concern.
Correction: A previous version of this update mistakenly reported that Singapore has reported to the IAEA that it had detected very small amounts of iodine-131 and cesium-137 in air. Singapore has not made such a report.