• English
  • العربية
  • 中文
  • Français
  • Русский
  • Español

You are here

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



Brief Update on State of Fukushima Daiichi Reactors

Japanese authorities today announced a number of developments at Fukushima Daiichi nuclear power plant, where reactor cooling systems were disabled following the massive earthquake and tsunami on 11 March.

At Units 1, 2, 3 and 4, workers have advanced the restoration of off-site electricity, and the lights are working in Unit 3's main control room.

Black smoke was seen emerging from the Unit 3 reactor building, spurring the temporary evacuation of workers from Units 3 and 4. The emission of smoke has now decreased significantly.

Crews continued today to use a concrete pump truck to deliver high volumes of water into the Unit 4 spent fuel pool, where there are concerns of inadequate water coverage over the fuel assemblies.

At Units 5 and 6, workers have successfully restored off-site power to the reactor, which had previously reached a safe, cold shutdown status.



→ Technical Briefing on Situation in Japan
→ Watch Video

On Wednesday, 23 March 2011, Graham Andrew, Special Adviser to the IAEA Director General on Scientific and Technical Affairs, briefed both Member States and the media on the current status of nuclear safety in Japan. His opening remarks, which he delivered at 15:30 UTC at the IAEA headquarters in Vienna, are provided below:

  • There are some positive developments related to the availability of electrical power supply to the Fukushima Daiichi nuclear power plants, although the overall situation remains of serious concern.
  • AC power is now available at Units 1, 2 and 4. Power has been restored to some instrumentation in all Units except Unit 3. At Unit 3, the main control room has lighting, but no power to its equipment or instruments. As a positive development instrumentation, as it becomes available, is providing more data that can be assessed by experts.
  • The pressure in the reactor pressure vessel and drywell of Unit 3 is stable. However, pressure has increased in both the reactor pressure vessel and the drywell of Unit 1, where seawater injection has been increased. Until heat can be removed from Unit 1, pressure tends to increase as water is injected. The reactor feed water system is being used, in addition to water injection through fire extinguisher lines.
  • Pressure readings in Unit 2 appear to be less reliable. Only limited data is available concerning the reactor pressure vessel and reactor containment vessels' integrity of Unit 2. Temperature readings in the reactor pressure vessels of Units 1 and 3 were high and of some concern. The temperature has now dropped in Unit 1 following the start of seawater injection via feed-water pipes. Indications are that the temperature at Unit 2 is stable.
  • Units 5 and 6 continue to have off-site power and remain in cold shutdown.
  • Dose rates measured in the containment vessels and suppression chambers of Units 1, 2 and 3 are available and are being studied.
  • Periodic water spraying of Units 2, 3, and 4 and the common spent fuel pool has continued.

Radiation Monitoring

The IAEA radiation monitoring team took additional measurements at distances from 30 to 73 km from the Fukushima nuclear power plant. Results from gamma dose-rate measurements in air ranged from 0.2 to 6.9 microsievert per hour. The beta-gamma contamination measurements ranged from 0.02 to 0.6 Megabecquerel per square metre.

The second IAEA monitoring team has now arrived in Japan. The two teams in Japan will continue to work closely with the Japanese authorities. Monitoring will be undertaken in the areas of Fukushima and Tokyo. Measurements will be taken to determine more precisely the actual composition of the radionuclides that have been deposited.

More data has become available from the Japanese authorities. The measurements indicate that the radiation dose rates at the Daiichi site are decreasing. Absent further releases from the site, this is to be expected as relatively short lived radionuclides such as Iodine-131 decay away. At the Daiini site, small spikes have been observed in gamma dose rate measurements; these are most likely to be the result of releases carried by the wind from the nearby Daiichi site.

The deposition of iodine-131 and caesium-137 varies across some ten Prefectures from day to day, but the trend is generally upward. In contrast, environmental radiation monitoring data in the Fukushima Prefecture outside the 20km evacuation zone, shows mostly decreasing values.

Monitoring of the marine environment is being undertaken by the Japanese Ministry of Education, Culture, Sport, Science and Technology (MEXT). High levels of iodine-131 and caesium-137 were measured close to the effluent discharge points Units 1 to 4 of Fukushima Daiichi (i.e. before dilution by the ocean). Future monitoring will cover eight locations 30 km off the coast at 10 km intervals. Results for seawater and the atmosphere above the sea should be available in the next few days. IAEA experts from the Environment Laboratories Monaco will assess this data.

Since yesterday, the IAEA has received further information from the Japanese Ministry of Health, Labour and Welfare regarding the presence of radioactivity in milk, drinking water and vegetables. The results of some samples were above the limits specified in Japanese regulations concerning limits for food and water ingestion.

In Fukushima prefecture six raw milk samples, and in Ibaraki prefecture three spinach samples, showed concentrations of Iodine-131 in excess of limits. We understand that the Prime Minister of Japan, Mr. Naoto Kan, has today issued instructions to food business operators to cease, for the time being, the distribution of, and for the public to cease the consumption of, certain leafy vegetables (e.g. spinach, komatsuna, cabbages) and any flowerhead brassicas (broccoli, cauliflower) produced in Fukushima Prefecture. The Prime Minister has ordered food business operators not to distribute, for the time being, any fresh raw milk and parsley in Ibaraki Prefecture.

We have also been advised that the Ministry of Health, Labour and Welfare has encouraged Ibaraki and Chiba Prefectures to monitor seafood products.

The Tokyo Metropolitan Water Office stated that levels of iodine-131 in tap water at a purification plant were found to be above the limits for drinking water for infants but below the level for adults. The Ministry of Health Labour and Welfare, has requested that tap water in Tokyo is not used as drinking water for infants.

So, in summary: there are some positive indications on the site; precautionary restrictions around the site on certain foodstuffs; and monitoring of the environment is continuing beyond the evacuation zone and at sea. No significant risk to human health has been identified.



Restoring Power to Fukushima Daiichi

Without electrical power, cooling systems at Fukushima Daiichi's six reactors cannot operate. Many of the problems facing the nuclear power plant stem from the loss of electrical power at the site following the massive earthquake and tsunami on 11 March. The earthquake cut off external power to the plant and the tsunami disabled backup diesel generators.

Japanese officials have been working to restore power to the facility, and their efforts are organized in three phases.

Units 1 and 2

Reactor cooling systems at these units are severely hampered. There is suspected damage to the nuclear fuel in both units. Workers successfully connected off-site electrical supplies to a transformer at Unit 2 on 19 March and later to at least one electrical distribution panel inside the plant. Technicians are conducting diagnostic tests to determine the integrity of the reactor's electrical systems.

Japanese authorities plan to connect Unit 1 sometime after Unit 2. Because of the degraded condition of the Unit 1 reactor building, this work may take more time compared to Unit 2, the reactor building sustained significantly less damage since the earthquake struck.

Units 3 and 4

Reactor cooling systems at Unit 3 are severely hampered. There is suspected damage to the reactor's fuel, and the condition of its spent fuel pool is uncertain. Unit 4 had been shut down for routine maintenance - and all its fuel was removed to the reactor building's spent fuel pool - prior to the earthquake. There is therefore no concern about fuel in the reactor core, but considerable concern about the fuel in the spent fuel pool.

Workers are moving toward restoring electricity to both units, but their progress is uncertain.

Units 5 and 6

Both units had been shut down for routine maintenance prior to the earthquake, reducing their cooling needs somewhat, but not entirely. On 17 March operators were able to start one of the Unit 6 diesel generators. On 19 March, workers successfully connected the second diesel generator in Unit 6. The two generators were used to power cooling systems in both reactors, which then achieved a safe, cold shutdown configuration. Off-site power was restored to Unit 5 on 21 March.

Restoring external power to the power plant does not mean the reactors will immediately resume normal safety function. The earthquake and tsunami may have inflicted considerable damage in addition to knocking out electricity supplies. Since the extent of this damage (and therefore the extent of necessary repair) is unknown, it is not possible to accurately estimate a work schedule. Progress of efforts to restore power may be impaired by heavy gloves or respirators required to permit the operators to work in the reactors following the damage inflicted by the earthquake and tsunami.

As power is restored, workers will perform checks to make certain the conditions are safe to restart individual components. They will check for grounds and ensure circuits remain intact. If damage is discovered, a decision will have to be made whether to perform repairs or move on to the next component on a prioritized list. Nuclear reactors, especially safety related equipment, incorporate multiple layers of redundancy. So a problem in one component does not necessarily mean a specific safety function will be unrecoverable. It is more likely that operators will move on to the redundant equipment in an effort to determine the most intact system and focus their restoration efforts there. This process takes time.

Last update: 27 Jul 2017

Stay in touch