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International Atomic Energy Agency Japan Earthquake Update, 20 March (15:30 UTC)


Vienna, Austria–(ENEWSPF)–20 March 2011 – 15:30 UTC.  On Sunday, 20 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 have been some positive developments in the last 24 hours, but the overall situation at the Fukushima Daiichi nuclear power plant remains very serious.

Efforts to restore electrical power to the site continue. Off-site electrical power has been connected to the local substation for Unit 2 today. Work is continuing under difficult conditions to connect power from the substation to the reactor building. Seawater is still being injected into the reactor pressure vessels of Units 1, 2 and 3. Water injection is not needed for Unit 4 as the reactor is in outage.

White smoke or vapour from Unit 3 is still being observed, but it is less intense than on previous days. Spraying of the reactor building with water is in progress. Following an initial rise in pressure in the Unit 3 reactor pressure vessel, plans were made to vent the vessel should it become necessary. However, from information recently provided by NISA they have decided not to vent as the vessel pressure has started to reduce.

The situation in the reactor spent fuel pools is relatively stable, but is still of concern. Spraying of water into the pool of Unit 4 started yesterday. The Agency still lacks data on water levels and temperatures at the spent fuel pools at Units 1, 2, 3 and 4.

A positive development is that cooling has been restored to the reactor pressure vessels in Units 5 and 6. Temperatures in the spent fuel pools at these two units, which had been rising in the last few days, have now fallen significantly to around 40 degrees centigrade from a maximum of about 69 degrees yesterday. Two diesel generators, one for each Unit, are providing electricity.

2. Radiation Monitoring

Radiation levels in major Japanese cities have not changed significantly since yesterday and remain below those which are dangerous to human health.

The IAEA radiation monitoring team took additional measurements yesterday between Tokyo and locations up to 150 km from the Fukushima site. Dose rates were typically a few microsieverts per hour compared to a typical background level of around 0.1 microsieverts per hour.

From the measurements taken within the exclusion zone, no significant alpha radiation has been detected so far.

This morning, we received additional data from the Agency’s monitoring team which indicated contamination on the ground at a location 50 to 70 km from the Fukushima site. The team will make confirmatory measurements tomorrow at the same locations to help validate the initial results. Grass and other samples have also been taken by the team from various locations in the Fukushima Prefecture for analysis. In the coming days, the IAEA monitoring team plans to take measurements at the same locations monitored by the Japanese authorities. This will assist in the validation of measurements. The IAEA is sending additional monitoring experts to Japan to supplement its capabilities in the field.

Some results on the monitoring of foodstuffs have been made available by Japan to the IAEA and FAO. We can confirm measurements indicating that, in some areas, Iodine-131 in milk and in freshly grown leafy vegetables, such as spinach and spring onions, is significantly above the levels set by Japan for restricting consumption of these food products.

3. Agency Activities

The Director General has returned to Vienna and will brief the Board of Governors on Monday on the outcome of his visit to Tokyo.

Japan Earthquake Update (20 March 2011, 16:20 UTC)

Japanese authorities have notified the IAEA of progress at the Fukushima Daiichi nuclear power plant. Workers today have successfully placed reactor Unit 5 (at 05:30 UTC) and 6 (at 10:27 UTC) into cold shutdown.

This means that the reactors are in a safe mode, with cooling systems stable and under control, and with low temperature and pressure within the reactor.

Officials are continuing efforts to restore plant systems at Daiichi Units 1-3.

Unit 4 had been shut down for maintenance, with all its fuel removed from the reactor core, before the 11 March earthquake.

Eight other reactors at the Fukushima Daini, Onagawa, and Tokai nuclear power plants were shut down automatically after the earthquake and all are now in cold shutdown.

Japanese Earthquake Update (20 March 2011 14:00 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 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.

The concern about the spent fuel pools at Fukushima Daiichi is that sources of power to cool the pools have 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.

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.)

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.

Source: iaea.org

 


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