ISSN 2330-717X

Japan: IAEA Lastest Briefing On Fukushima Nuclear Crisis

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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).

Fukushima Nuclear Power Plant
Fukushima Nuclear Power Plant

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 25th 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.

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