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IAEA BRIEFING ON FUKUSHIMA NUCLEAR ACCIDENT (27 April 2011, 18:00 UTC)
→ Summary of Reactor Status
On Wednesday, 27 April 2011, the IAEA provided the following information on the current status of nuclear safety in Japan:
1. Current Situation
Overall, the situation at the Fukushima Daiichi nuclear power plant remains very serious, but there are signs of recovery in some functions, such as electrical power and instrumentation.
Changes to Fukushima Daiichi Nuclear Power Plant Status
The IAEA receives information from various official sources in Japan through the Japanese national competent authority, the Nuclear and Industrial Safety Agency (NISA).
Management of On-site Contaminated Water
According to the 25 April evaluation by NISA of the report submitted by the Tokyo Electric Power Company (TEPCO), there is a little less than 70 000 tonnes of stagnant water with high-level radioactivity in the basement of the turbine buildings of Units 1, 2 and 3.
On 25 April the power supply for the temporary electrical pumps that supply water to the reactor pressure vessel of Units 1, 2 and 3 was switched from the off-site power supply to temporary diesel generators to allow work to enhance the off-site power supply. The power supply has now been returned to the off-site supply.
White "smoke" continues to be emitted from Units 2 and 3. No more white "smoke" was seen coming from Unit 4 as of 21:30 UTC on 25 April.
In Unit 1 fresh water is being continuously injected into the reactor pressure vessel through the feedwater line at an indicated flow rate of 6 m3/h using a temporary electric pump with off-site power.
In Unit 2 and Unit 3 fresh water is being continuously injected into the reactor pressure vessel through the fire extinguisher line at an indicated rate of 7 m3/h using temporary electric pumps with off-site power.
In Unit 4 140 tonnes of fresh water was sprayed over the spent fuel pool on 23 April and 165 tonnes of fresh water was sprayed over the spent fuel pool on 24 April using a concrete pump truck. The nuclear emergency response headquarters reported that temperature measurements showed the spent fuel pool temperature to be 83 °C before spraying and 66 °C after spraying on 23 April, and the spent fuel pool temperature to be 86 °C before spraying and 81 °C after spraying on 24 April.
Nitrogen gas continues to be injected into the containment vessel in Unit 1 to reduce the possibility of hydrogen combustion in the containment vessel. The pressure in the reactor pressure vessel is increasing.
The reactor pressure vessel temperatures in Unit 1 remain above cold shutdown conditions. The indicated temperature at the feedwater nozzle of the reactor pressure vessel is 134.7 °C and at the bottom of reactor pressure vessel is 110.9 °C.
The reactor pressure vessel temperatures in Unit 2 remain above cold shutdown conditions. The indicated temperature at the feed water nozzle of the reactor pressure vessel is 121.2 °C. The reactor pressure vessel and the dry well remain at atmospheric pressure. Fresh water injection (a total of 135 tonnes) to the spent fuel pool via the spent fuel pool cooling line was carried out from 19 to 25 April.
The temperature at the bottom of the reactor pressure vessel in Unit 3 remains above cold shutdown conditions. The indicated temperature at the feed water nozzle of the reactor pressure vessel is 67.9 °C and at the bottom of the reactor pressure vessel is 110.4 °C. The reactor pressure vessel and the dry well remain at atmospheric pressure.
There has been no change in the status in Unit 5 or Unit 6 or in the common spent fuel storage facility.
2. Radiation Monitoring
On 25 April deposition of Cs-137 was detected in five prefectures, the values reported ranging from 3.2 to 20 Bq/m2.
Gamma dose rates are measured daily in all 47 prefectures. A general decreasing trend has been observed in all locations since around 20 March. For Fukushima prefecture, gamma dose rates in recent days were in the range 1.7-1.8 µSv/h. In Ibaraki prefecture, gamma dose rates were slightly below 0.12 µSv/h. In all other prefectures, reported gamma dose rates were below 0.1 µSv/h with similar decreasing trends.
Gamma dose rates reported specifically for the eastern part of Fukushima prefecture, for distances beyond 30 km from Fukushima Daiichi, showed a similar general decreasing trend, ranging from 0.1 to 19.4 µSv/h, as reported on 25 April. The other 45 prefectures had gamma dose rates of below 0.1 µSv/h, falling within the local natural background range.
In drinking water, I-131 or Cs-137 is detectable, but in only a few prefectures. As of 1 April, the one remaining restriction on the consumption of drinking water relating to I-131 (at a level of 100 Bq/L) applies to only one village in the Fukushima prefecture, and the restriction applies only to infants.
Food monitoring data were reported by the Japanese Ministry of Health, Labour and Welfare on 26 April for a total of 39 samples taken on 22 and 24 - 26 April from eight prefectures (Chiba, Fukushima, Gunma, Hokkaido, Ibaraki, Kanagawa, Niigata and Yamagata). Analytical results for all of the samples of various vegetables, mushrooms, beef, seafood and raw unprocessed milk indicated that I-131, Cs-134 and Cs-137 were either not detected or were below the regulation values set by the Japanese authorities.
3. Marine Monitoring
Marine Monitoring Programmes
The marine monitoring programme is carried out both near the discharge areas of the Fukushima nuclear power plant by TEPCO and at off-shore stations by the Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT). The locations of the sampling positions, including several new additional positions, were given in the briefing of 26 April (see Fig. B: Locations of TEPCO and MEXT Seawater Sampling Positions). Contamination of the marine environment occurred by aerial deposition and by discharges and outflow of contaminated water.
Monitoring at off-shore sampling positions consists of:
- Measurement of ambient dose rate in air above the sea;
- Analysis of ambient dust above the sea;
- Analysis of surface samples of seawater; and
- Analysis of samples of seawater collected at 10 m above the sea bottom.