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Fukushima Nuclear Accident Update Log

Chronology of Updates:
2 June | 12-18 May | 4-11 May | 5 May | 3 May | 2 May | 28 April | 27 April | 26 April | 21 April | 20 April | 19 April | 18 April | 15 April | 14 April | 13 April | 12 April | 11 April | 10 April | 9 April | 8 April | 7 April | 6 April | 5 April | 4 April | 3 April | 2 April | 1 April | 31 March | 30 March | 29 March | 28 March | 27 March | 26 March | 25 March | 24 March | 23 March | 22 March | 21 March | 20 March | 19 March | 18 March | 17 March | 16 March | 15 March | 14 March | 13 March | 12 March | 11 March | Full Update



The IAEA has been informed by Japanese authorities that fresh water is now being used in place of sea water to cool the reactor pressure vessels at Units 1, 2 and 3 at the Fukushima nuclear power plant. The switch to fresh water is preferable as it leaves fewer deposits in components and is less corrosive than sea water.



→ Summary of Reactor Status

On Saturday, 26 March 2011, Graham Andrew, Special Adviser to the IAEA Director General on Scientific and Technical Affairs, provided the following briefing on the current status of nuclear safety in Japan:

1. Current Situation

The situation at the Fukushima Daiichi plant remains very serious.

The restoration of off-site power is still progressing and instrumentation is being tested in Units 1, 2 and 4.

At Unit 1, the main change is the injection of freshwater to the Reactor Pressure Vessel (RPV). The temperature measured at the bottom of the RPV is stable at 144 °C. Pressure in the RPV, containment vessel and suppression pool have come back down after having increased from 22 to 24 March.

At Unit 2, the injection of freshwater to the RPV commenced at 01:00 on 26 March. The RPV temperature is stable at 100 °C at the bottom of the RPV. The pressure measured in the RPV and in the containment pressure vessel is stable at circa one atmosphere. Freshwater is also being injected in the RPV of Unit 3. Temperature measurement at the feed-water nozzle of Unit 3's RPV is still judged to be unreliable, but at the bottom of the RPV it is stable at 102 °C. White "smoke" continues to be emitted as of 23:00 UTC on 25 March from Unit 3, as it does from Unit 4Unit 3 shows a consistently low containment drywell pressure of circa 1 atmosphere.

There have been high radiation readings in Units 1 and 3, the likelihood of damage to the containment integrity of Unit 3 is a cause for concern.

We understand that a total of 17 TEPCO workers and contractors have received doses between 100 and 180 millisievert. TEPCO measured the dose rate of 400 millisievert per hour above the surface of the water in the Unit 3 turbine building where 2 workers had been contaminated.

Units 5 and 6 are still in cold shutdown, with slight variations in RPV water temperatures (down a few degrees at Unit 5, up a few at Unit 6).

2. Radiation Monitoring

Deposition of radioactivity is monitored daily by Japanese authorities in all 47 prefectures. From 24 to 25 March, the daily level of deposition decreased in all but one prefecture. The highest value was observed in the prefecture of Ibaraki, where on 25 March a deposition of 480 becquerel per square metre for iodine-131 was observed; the highest value for caesium 137 was measured in Yamagata at 150 becquerel per square metre. For the Shinjyuku district of Tokyo, the additional deposition of iodine-131 and caesium-137 on 25 March was below 200 becquerel per square metre.

Monitoring of the marine environment has continued. New data for 21 to 25 March on radionuclide concentrations were made available for the discharge area 330 metres south of the pipeline of Fukushima Daiichi. The levels are generally quite high and vary significantly with time. The highest levels were detected at 25 March with, for example, 50 000 becquerel per litre of iodine-131, 7,200 becquerel per litre of caesium-137, and 7 000 becquerel per litre of caesium-134. Other short lived radionuclides were also reported. No new data has been reported by Japan from the monitoring stations located about 30 km offshore.

Monitoring of drinking water is on-going: iodine-131 in drinking water was detected on 24 March in 12 prefectures, whereas caesium-137 was detected in 6 of the 47 prefectures. In Tochigi, a value of 110 becquerel per litre was observed, which is above the recommended value for drinking water to be consumed by infants (i.e. 100 becquerel per litre). All other measurements were far below 100 becquerel per litre. All caesium-137 concentrations measured were lower than 10 becquerel per litre, which is significantly below the limit set by Japan of 200 becquerel per litre.

Environmental monitoring of soil, surface water, vegetation and air continues to be carried out in the Fukushima prefecture. The monitoring results indicate high levels of contamination. The values reported are generally consistent with measurements of gamma dose rates and beta-gamma contamination carried out by an IAEA monitoring team.

Two IAEA teams are currently monitoring in Japan. One team made gamma-dose rate measurements in Tokyo and the south of Tokyo in the prefecture of Kanagawa. Gamma-dose rates ranged from 0.05 to 0.2 microsievert. Another monitoring team made additional measurements at distances of 23 to 97 km (in a southerly and south westerly direction) from the Fukushima nuclear power plant. At these locations, the dose rates ranged from 0.73 to 8.8 microsievert per hour. At the same locations, results of beta-gamma contamination measurements ranged from 0.02 to 0.4 Megabecquerel per square metre.

Two prefectures (Ibaraki, Tochigi) reported iodine-131 in unprocessed raw milk, but the measurement results were below the regulation values set by the Japanese authorities. In addition, iodine-131 was not detected in any of the samples taken from the remaining four prefectures (Chiba, Gunma, Kanagawa and Saitama) and Tokyo. Caesium-137 was not detected in any of the samples.

For two prefectures (Ibaraki, Tochigi) iodine-131 and cesium-137 were reported in spinach and other leafy vegetables above the regulation values set by the Japanese authorities. However, iodine-131 and caesium-137 were either not detected or were below the regulation values, in all of the samples taken from the remaining four prefectures (Chiba, Gunma, Kanagawa and Saitama) and Tokyo. In all six prefectures and Tokyo, no iodine-131 and caesium-137 were detected in leeks, or measurements were well below the regulation values set by the Japanese authorities.



IAEA Sends Second and Third Teams to Japan to Aid Response to Nuclear Emergency

The IAEA has dispatched additional teams to Japan to assist in the response to the Fukushima Daiichi nuclear power plant emergency.

On 24 March, a team of IAEA specialists travelled to Japan, where they will continue efforts to supplement Japan's radiation monitoring efforts. Team members include worker radiation protection experts and safeguards department officials.

On 25 March, a joint IAEA/Food and Agriculture Organization team departed Vienna. The three-person team included the Head of the IAEA Food and Environmental Protection Laboratory, an IAEA soil scientist, and an FAO food safety specialist from FAO's headquarters in Rome.

This food safety assessment team will provide advice and assistance on sampling and analytical strategies and will help interpret Japanese monitoring data.



Brief Update on State of Fukushima Daiichi Reactors

Japanese authorities today confirmed a number of developments at the nuclear reactors at Fukushima Daiichi.

Unit 1

Workers have restored lighting in the control room and have recovered some instrumentation. As of 25 March, fresh water is now being pumped into the reactor pressure vessel (RPV) instead of seawater.

Unit 2

Seawater injection into the reactor pressure vessel continues, and RPV pressures remain stable.

Unit 3

Workers are now pumping fresh water into the RPV, while seawater is pumped into the spent fuel pool. In addition, firefighters sprayed water into the reactor building yesterday from the outside.

Unit 4

With no fuel in the RPV, concerns remain focused on the condition of the spent fuel pool, and workers continued to use a concrete pump truck to pour water into the pool from above while pumping seawater into the pool through the fuel pool cooling line.

Units 5 and 6

Both reactors have achieved safe, cold shutdown, and their fuel pool temperatures have stabilised at acceptable levels.



Radioactive Materials Found in Japanese Seawater Sampling - Updated

Japanese authorities today reported data on radiation samples collected 30 kilometres off shore of the Fukushima Daiichi nuclear power plant on 24 March, and the levels of iodine-131 and cesium-137 showed slight variations from data collected at the same locations on 23 March (See previous update).

A vessel from the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) collected water samples at eight points 30 kilometres from the coastline and found measurable concentrations of iodine-131 and cesium-137. The iodine concentrations measured were about at Japanese regulatory limits, and the cesium levels were well below those limits.

The IAEA's Environment Laboratories Monaco has received the data and offered this preliminary analysis:

Dilution, both into deeper layers and by dispersion along the prevailing ocean currents will lead to a rapid decrease of the initial surface contamination.

For the short term, iodine-131 will be the relevant radionuclide as far as doses are concerned, but for the long term, cesium-137 will be the more important radionuclide in the marine environment. It will be possible to follow this nuclide over long distances for several years.

It can be expected that radionuclides will take months or years to reach other shores of the Pacific. The main transport of contamination takes place by atmospheric transport over long distances.

Last update: 27 Jul 2017

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