Vienna, Austria--(ENEWSPF)--22 March 2011 -18:00 UTC.
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 irradiated 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.
Nuclear power plants must replace fuel every one to two years, and the Fukushima Daiichi reactors typically remove about 25 percent of the reactor's fuel - to be replaced with fresh, or unirradiated, fuel - during each refuelling outage. The spent fuel, which is hottest immediately after it is removed from the reactor, is placed in the spent fuel pool until it is cool enough to be moved to longer-term storage.
The concern about the spent fuel pools at Fukushima Daiichi is that the capability to cool the pools has been compromised. See diagram below for location of the pool in each reactor building.
Elevated radiation measurements at the site may be partially of the result of uncovered or overheated spent fuel.
Number of Fuel Assemblies in Cooling Pools at Fukushima Daiichi - (Reported 17 March by Japan's Ministry of Economy, Trade and Industry)
|Capacity||Irradiated Fuel Assemblies||Unirradiated Fuel Assemblies||Most Recent Additions of Irradiated Fuel|
|Unit 1||900||292||100||March 2010|
|Unit 2||1,240||587||28||Sept 2010|
|Unit 3||1,220||514||52||June 2010|
|Unit 4||1,590||1,331||204||Nov 2010|
|Unit 5||1,590||946||48||Jan 2011|
|Unit 6||1,770||876||64||Aug 2010|
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 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.
Precise information on the status of the spent fuel pool was unavailable in the days following the earthquake, but Japan's Nuclear and Industrial Safety Agency began to release temperature data on 20 March:
|20 March, 23:00 UTC:||49 °C|
|21 March, 05:25 UTC:||50 °C|
|21 March, 21:20 UTC:||51 °C|
|22 March, 02:20 UTC:||53 °C|
|22 March, 06:30 UTC:||50 °C|
Workers conducted an operation to spray 40 tonnes of seawater to the spent fuel pool on 20 March.
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 21 March, emergency workers have sprayed water from fire trucks and other vehicles, so far spraying at least 3,742 tonnes.
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 on 20 March, and have continued daily since then, so far spraying at least 255 tonnes.
Units 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 below).
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 confirmed as of 18 March that fuel assemblies there were fully covered by water, and the temperature was 57 °C as of 20 March, 00:00 UTC. Workers sprayed water over the pool on 21 March for nearly five hours, and the Nuclear and Industrial Safety Agency reported that the pool temperature had risen to 61 °C as of 21 March, 07:30 UTC.
Fukushima Nuclear Accident Update (22 March 2011, 16:45 UTC)
Seawater Monitoring - Updated
Japanese authorities have reported that the Tokyo Electric Power Company has detected radioactive materials in seawater at one location near the Southern discharge canal at the Fukushima Daiichi nuclear power plant. Samples taken included levels of iodine-131, cesium-134, and cesium-137.
To study a larger area of the marine environment, the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) plans to measure radioactivity around the plant from 22-23 March. Seawater will be collected from eight locations, and the Japan Atomic Energy Agency plans to analyse the samples and release results on 24 March. The analysis will include radionuclide concentrations found in sea water and dose rate in the air. The IAEA will continue to follow this information.
IAEA Briefing on Fukushima Nuclear Emergency (22 March 2011, 15.30 UTC)
On Sunday, 22 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:
1. Current Situation
There continue to be some improvements at the Fukushima Daiichi nuclear power plant, but the overall situation remains very serious. High levels of contamination have been measured in the locality of the plant.
On the Fukushima site the highest concern remains the spent fuel in the storage ponds of each reactor unit, particularly Unit 4. Reactor Units1-3 remain of concern, in particular Unit 2.
We have not received validated information for some time related to the containment integrity of Unit 1 so we are concerned that we do not know its exact status. Grey smoke was observed from Unit 3 which led to the evacuation of plant personnel for several hours yesterday due to elevated dose rates. In addition, white smoke or vapour was observed from Unit 2. Efforts continue in Unit 2 to connect AC to pumps etc. Work for the recovery of off-site power supply to Units 3 and 4 is also proceeding.
Seawater is being injected into the reactor vessels of Units 1, 2 and 3. Water is being sprayed periodically into the spent fuel pools at Units 2, 3 and 4 but no information is available for the spent fuel pool of Unit 1. The Agency still lacks data on water levels and temperatures in the spent fuel pools at Units 1, 3 and 4.
There have been some positive developments concerning Units 5 and 6 that are in cold shutdown: off-site power is now being used in Unit 5; the pressure of the reactor pressure vessel of both units has decreased; and water is being injected in to the reactor pressure vessel, as needed.
2. Radiation Monitoring
IAEA monitoring of gamma dose rates and beta-gamma contamination has continued over the last 24 hours. This has been carried out together with the Japanese authorities to facilitate the comparison of results.
The IAEA took measurements at additional locations between 35 to 68 km from the Fukushima plant. The dose-rate results ranged from 0.8 to 9.1 microsieverts per hour. The beta-gamma contamination measurements ranged from 0.08 to 0.9 MBq per square metre. More precise interpretation of the results will be possible based on measurements to be made of the composition of the radioactive material that has been released.
In the coming days the IAEA will have two monitoring teams in Japan. One team will be in the Fukushima area and a separate team will undertake monitoring in Tokyo and the surrounding area.
The Agency continues to receive data confirming high levels of radioactivity in food, notably spinach, in samples taken from 37 locations in the vicinity of five cities south of the Fukishima site. This indicates that in four Prefectures some food products are above permissible levels. High levels of both Iodine-131 and Caesium-137 have been measured by the Japanese authorities in spinach and some other fresh vegetables, together with Iodine-131 in milk. However, as reported yesterday, distribution of food from the areas affected has been restricted. The Japanese authorities are monitoring the situation in the rest of the country. Further monitoring data will be provided by Japan to the IAEA/FAO on an ongoing basis.
Japan's Nuclear and Industrial Safety Agency (NISA) has announced that contamination has been found in sea water samples taken close to the outlet of the Fukushima Daiichi plant. We have been informed by NISA about plans to monitor the marine environment.