Spent Fuel Pools at Fukushima Daiichi Nuclear Power Plant -- UPDATED
Spent fuel removed from a nuclear reactor is highly radioactive and generates intense heat. This fuel needs to be actively cooled for one to three years in pools that cool the fuel, shield the radioactivity, and keep the fuel in the proper position to avoid fission reactions. If the cooling is lost, the water can boil and fuel rods can be exposed to the air, possibly leading to severe damage and a large release of radiation.
Elevated radiation measurements at the site may be partially of the result of uncovered or overheated spent fuel.
Here is a summary of spent fuel conditions at Fukushima Daiichi nuclear power plant, based on documents and confirmed by Japanese officials (new information in bold):
Unit 1
Unit 1 experienced an explosion on 12 March that destroyed the outer shell of the building's upper floors. No precise information has been available on the status of the spent fuel pool.
Unit 2
No precise information has been available on the status of the spent fuel pool. Authorities began adding 40 tonnes of seawater to the spent fuel pool on 20 March.
Unit 3
Unit 3 experienced an explosion on 14 March that destroyed the outer shell of the building's upper floors. The blast may have damaged the primary containment vessel and the spent fuel pool. Concerned by possible loss of water in the pool, authorities began spraying water into the building in an effort to replenish water levels. First, helicopters dropped seawater on 17 March, and every day since then, including today, emergency workers have sprayed water from fire trucks and other vehicles.
Unit 4
This reactor was shut down 30 November 2010 for routine maintenance, and all the fuel assemblies were transferred from the reactor to the spent fuel pool, before the 11 March earthquake. The heat load in this pool is therefore larger than the others.
On 14 March, the building's upper floors were severely damaged, possibly causing a reduction of cooling capability in the spent fuel pool. Emergency workers began spraying water into the building today.
Unit 5 and 6
Instrumentation at these reactors began to indicate rising temperatures at their spent fuel pools starting on 14 March. Three days later, Japanese technicians successfully started an emergency diesel generator at Unit 6, which they used to provide power to basic cooling and fresh-water replenishment systems. Workers created holes in the rooftops of both buildings to prevent any hydrogen accumulation, which is suspected of causing earlier explosions at Units 1 and 3.
A second generator came online on 18 March, and the next day, the higher-capability Residual Heat Removal system recovered full function. Temperatures in the spent fuel pools of Units 5 and 6 have gradually returned to significantly lower temperatures. (See graph at left.)
Instrumentation at these reactors began to indicate rising temperatures at their spent fuel pools starting on 14 March. Three days later, Japanese technicians successfully started an emergency diesel generator at Unit 6, which they used to provide power to basic cooling and fresh-water replenishment systems. Workers created holes in the rooftops of both buildings to prevent any hydrogen accumulation, which is suspected of causing earlier explosions at Units 1 and 3.
A second generator came online on 18 March, and the next day, the higher-capability Residual Heat Removal system recovered full function. Temperatures in the spent fuel pools of Units 5 and 6 have gradually returned to significantly lower temperatures. (See graph at left.)
Common Use Spent Fuel Pool
In addition to pools in each of the plant's reactor buildings, there is another facility -- the Common Use Spent Fuel Pool -- where spent fuel is stored after cooling at least 18 months in the reactor buildings. This fuel is much cooler than the assemblies stored in the reactor buildings. Japanese authorities have confirmed that fuel assemblies there are fully covered by water, and the temperature was 57 ˚C as of 20 March, 00:00 UTC.
IAEA Briefing on Fukushima Nuclear Emergency (19 March 2011, 14:00 UTC)
On Saturday, 19 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 14:00 UTC at the IAEA headquarters in Vienna, are provided below:
1. Current Situation
The situation at the Fukushima Daiichi nuclear power plants is similar to that which I described yesterday.
Efforts to restore electrical power to the site continue. It is hoped that power will be restored to Unit 2 today, which will then act as a hub for restoring power to Unit 1. However, we do not know if the water pumps have been damaged and if they will work when power is restored.
Seawater is still being injected into the reactor pressure vessels of Units 1 and 2 and additional fire trucks have arrived, reinforcing the operation to spray water into the Unit 3 reactor building.
We still lack reliable validated data on water levels and temperatures at the spent fuel pools at Units 3 and 4.
Temperatures at the spent fuel pools in Units 5 and 6 have risen in the past few days but this does not give rise to immediate concern. Water continues to be circulated within the reactor pressure vessels and the spent fuel ponds at both units.
A second diesel generator is providing power for cooling at Units 5 and 6. We have been informed that holes have been made in the roof of the reactor building at Units 5 and 6 to avoid the risk of a hydrogen explosion.
2. Radiation Monitoring
Radiation levels in major Japanese cities have not changed significantly since yesterday.
The IAEA radiation monitoring team took measurements at seven different locations in Tokyo and in the Kanagawa and Chiba Prefectures. Dose rates were well below those which are dangerous to human health.
The monitoring team are now on their way to Aizu Wakamatsu City, which is 97 km west of the Fukushima nuclear power plant. They have just provided initial measurements from three additional locations.
Measurements made by Japan in a number of locations have shown the presence of radionuclides - ie isotopes such as Iodine-131 and Caesium-137 - on the ground.
This has implications for food and agriculture in affected areas. The IAEA and the UN Food and Agriculture Organization (FAO) are consulting with the Japanese authorities on measures being taken in these areas related to food and agriculture.
The Japanese Ministry of Health, Labour and Welfare has announced that radiation levels that exceeded legal limits had been detected in milk produced in the Fukushima area and in certain vegetables in Ibaraki. They have requested the Bureau of Sanitation at the Fukishima Prefectural Office, after conducting an investigation of the relevant information, to take necessary measures, such as identifying the provider of these samples and places where the same lots were distributed and banning sales based on the Food Hygiene Law. (Note: The text originally read out at the briefing was: "The Japanese Ministry of Health, Labour and Welfare informed the Agency that radiation levels exceeding legal limits had been detected in milk produced in the Fukushima area and in certain vegetables in Ibaraki. The Ministry ordered protective measures including a ban on sales of these products." An oral correction was made during the media briefing.)
We now have continuous online access to data from CTBTO radionuclide monitoring stations, which is being evaluated by Agency dosimetry specialists.
As far as the Fukushima Daini nuclear power plant is concerned, there is no record of any incidents or radiation releases at the site. Present elevated radiation levels at the Daini site are attributed by Japan to events at the Daiichi nuclear power plant.
3. Agency Activities
The Director General has left Tokyo for Vienna after meetings with senior government leaders and officials from the plant operator TEPCO.
As you know, he plans to brief the Board of Governors on Monday on the outcome of his trip.
→ Watch video : View Presentation
Japanese Earthquake Update (19 March 2011 12:00 UTC) - Corrected
Contamination in Food Products around Fukushima
(Please note correction posted 19 March at 15:30 UTC in bold in text below. Apologies for the inconvenience.)
The Japanese Ministry of Health, Labour and Welfare has confirmed the presence of radioactive iodine contamination in food products measured in the Fukushima Prefecture, the area around the Fukushima Daiichi nuclear power plant. According to the latest data, the food products were measured from 16-18 March and indicated the presence of radioactive iodine. To date, no other radioactive isotopes have been shown to increase in the analysis of food products around Fukushima.
Though radioactive iodine has a short half-life of about 8 days and decays naturally within a matter of weeks, there is a short-term risk to human health if radioactive iodine in food is absorbed into the human body. If ingested, it can accumulate in and cause damage to the thyroid. Children and young people are particularly at risk of thyroid damage due to the ingestion of radioactive iodine.
Japanese authorities have implemented two critical measures to counter the contamination of food products by radioactive iodine. First, on 16 March, Japan's Nuclear Safety Commission recommended local authorities to instruct evacuees leaving the 20-kilometre area to ingest stable (not radioactive) iodine. As an established method of prevention, the ingestion of stable iodine can help to prevent the accumulation of radioactive iodine in the thyroid. Stable iodine pills and syrup (for children) have been made available at evacuation centres. Second, the Ministry of Health, Labour and Welfare has requested an investigation into the possible stop of sales of food products from the Fukushima Prefecture.
The IAEA has passed this information to the Food and Agricultural Organization of the United Nations (FAO) and the World Health Organization (WHO) and will continue to report on this development.
According to materials on its website, the FAO is prepared to respond upon request from the Government of Japan in the following areas:
- assessing radioactive contamination of the agricultural environment, especially foods
- providing technical advice and determining appropriate medium- and long-term measures for agriculture -- including soil, land, forests, crops, fisheries, animal health and welfare and food safety
- facilitating international trade of foods, including agricultural produce
The IAEA continues to gather information on this development and will report further as events warrant.
Japan Earthquake Update (19 March 2011, 4:30 UTC)
Located on the Eastern coast of Japan, the six nuclear power reactors at Daiichi are boiling water reactors (BWRs). A massive earthquake on 11 March severed off-site power to the plant and triggered the automatic shutdown of the three operating reactors - Units 1, 2, and 3. The control rods in those units were successfully inserted into the reactor cores, ending the fission chain reaction.
The remaining reactors - Units 4, 5, and 6 -- had previously been shut down for routine maintenance purposes. Backup diesel generators, designed to start up after losing off-site power, began providing electricity to pumps circulating coolant to the six reactors.
Soon after the earthquake, a large tsunami washed over the reactor site, knocking out the backup generators. While some batteries remained operable, the entire site lost the ability to maintain proper reactor cooling and water circulation functions.
Here is the current status of the six reactors, based on documents and confirmed by Japanese officials (new information in bold):
Unit 1
Coolant within Unit 1 is covering about half of the fuel rods in the reactor, leading to fuel damage. High pressure within the reactor's containment led operators to vent gas from the containment. Later, an explosion destroyed the outer shell of the reactor building above the containment on 12 March.
There are no indications of problems with either the reactor pressure vessel or the primary containment vessel.
Efforts to pump seawater into the reactor core are continuing.
On 18 March, Japan assigned an INES rating of 5 to this unit. Further information on the ratings and the INES scale.
Unit 2
Coolant within Unit 2 is covering about half of the fuel rods in the reactor, leading to fuel damage. Following an explosion on 15 March, Japanese officials expressed concerns that the reactor's containment may not be fully intact. NISA officials reported on 18 March that white smoke continues to emerge from the building.
Efforts to pump seawater into the reactor core are continuing.
On 18 March, Japan assigned an INES rating of 5 to this unit.
Unit 3
Coolant within Unit 3 is covering about half of the fuel rods in the reactor, leading to fuel damage. High pressure within the reactor's containment led operators to vent gas from the containment. Later, an explosion destroyed the outer shell of the reactor building above the containment on 14 March.
Following the explosion, Japanese officials expressed concerns that the reactor's containment may not be fully intact. NISA officials reported on 18 March that white smoke continues to emerge from the building.
Efforts to pump seawater into the reactor core are continuing.
Of additional concern at Unit 3 is the condition of the spent fuel pool in the building. There are indications that there is an inadequate cooling water level in the pool, and Japanese authorities have addressed the problem by dropping water from helicopters into the building and spraying water from trucks. On 18 March, Japanese Self Defence Forces used seven fire trucks to continue spraying efforts. There is no data on the temperature of the water in the pool.
On 18 March, Japan assigned an INES rating of 5 to this unit.
All fuel had been removed from the reactor core for routine maintenance before the earthquake and placed into the spent fuel pool. A portion of the building's outer shell was damaged by the explosion at Unit 3 on 14 March, and there have been two reported fires - possibly including one in the spent fuel pool on 15 March -- that extinguished spontaneously, although smoke remained visible on 18 March.
Authorities remain concerned about the condition of the spent fuel pool.
On 18 March, Japan assigned an INES rating of 4 to this site.
Unit 5 and 6
Shut down before the earthquake, there are no immediate concerns about these reactors' cores or containment. Instrumentation from both spent fuel pools, however, has shown gradually increasing temperatures. Officials have configured two diesel generators at Unit 6 to power water circulation in the spent fuel pools and cores of Units 5 and 6.
Workers have opened holes in the roofs of both buildings to prevent the possible accumulation of hydrogen, which is suspected of causing explosions at other units.
Shut down before the earthquake, there are no immediate concerns about these reactors' cores or containment. Instrumentation from both spent fuel pools, however, has shown gradually increasing temperatures. Officials have configured two diesel generators at Unit 6 to power water circulation in the spent fuel pools and cores of Units 5 and 6.
Workers have opened holes in the roofs of both buildings to prevent the possible accumulation of hydrogen, which is suspected of causing explosions at other units.
Restoration of Grid
Progress has been achieved in restoring external power to the nuclear power plant, although it remains uncertain when full power will be available.
Evacuation
Japanese authorities have informed the IAEA that the evacuation of the population from the 20-kilometre zone around Fukushima Daiichi has been successfully completed. Japanese authorities have also advised people living within 30 kilometres of the plant to remain inside.
Iodine
On 16 March, Japan's Nuclear Safety Commission recommended local authorities to instruct evacuees leaving the 20-kilometre area to ingest stable (not radioactive) iodine. The pills and syrup (for children) had been prepositioned at evacuation centers. The order recommended taking a single dose, with an amount dependent on age:
Baby
12.5 mg
1 mo.-3 yrs.
25mg
3-13 yrs.
38mg
13-40 yrs.
76mg
40+ yrs.
Not necessary
Radiation Measurements
Radiation levels near Fukushima Daiichi and beyond have elevated since the reactor damage began. However, dose rates in Tokyo and other areas outside the 30-kilometre zone remain far from levels which would require any protective action. In other words they are not dangerous to human health.
At the Fukushima Daiichi nuclear plant, radiation levels spiked three times since the earthquake, but have stabilized since 16 March at levels which are, although significantly higher than the normal levels, within the range that allows workers to continue onsite recovery measures
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