IAEA — Fukushima Nuclear Accident Update (23 March 2011, 01:10 UTC)

[OKIsItJustMe]

http://www.iaea.org/newscenter/news/tsunamiupdate01.html

Fukushima Nuclear Accident Update Log

Staff Report

Fukushima Nuclear Accident Update (23 March 2011, 01:10 UTC)

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 prioritised 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.

Fukushima Nuclear Accident Update (22 March 2011, 23:15 UTC)

Summary of Conditions at Fukushima Daiichi Nuclear Power Plant

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 disabled 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 normal 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 from 22 March in bold):

Unit 1

Coolant within Unit 1 is covering about half of the fuel rods in the reactor, and Japanese authorities believe the core has been damaged. 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.

No precise information has been available on the status of the spent fuel pool.

On 18 March, Japan assigned an INES rating of 5 to this Unit.

→ Further information on http://www-news.iaea.org/news/topics/default.asp">ratings and http://www-ns.iaea.org/tech-areas/emergency/ines.asp">INES scale.

On 19 March, the containment vessel pressure indication was restored.

Unit 2

Coolant within Unit 2 is covering about half of the fuel rods in the reactor, and Japanese authorities believe the core has been damaged. Following an explosion on 15 March, Japanese officials expressed concerns that the reactor's containment may not be fully intact. As of 19 March, 11:30 UTC, officials could no longer confirm seeing white smoke coming from the building. Smoke had been observed emerging from the reactor earlier. White smoke/vapour was observed again from 9:22 UTC on 21 March and diminished to nearly invisible by 22:11 UTC the same day. During the time of smoke emission, an increase in radiation dose rates was reported at 9:30 UTC 21 March. TEPCO then ordered an evacuation of plant personnel, though workers returned as of 00:00 UTC 22 March.

Efforts to pump seawater into the reactor core are continuing.

On 20 March, workers began pumping 40 tonnes of seawater into the spent fuel pool. Spent fuel temperature remains relatively stable with readings between 49°C and 53°C.

Restoration work to return power to all units continues, with progress at Unit 2 the most advanced. A distribution panel (power center) of Unit 2 has been connected to off-site electricity supply, and individual components in the unit are being checked prior to being energized.

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, and Japanese authorities believe the core has been damaged. 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. Indicated containment pressure has stabilized over the past 24 hours.

Following the explosion, Japanese officials expressed concerns that the reactor's containment may not be fully intact. White smoke has been seen emerging from the reactor, but on 19 March it appeared to be less intense than in previous days. Grey smoke was observed on 21 March in the southeast corner of Unit 3 from 6:55 UTC. After two hours this smoke turned to a white color and gradually diminished. By 22:11 21 March, the smoke was observed to be "ceasing." As reported under the Unit 2 update, during the time of smoke emission, an increase in radiation dose rates was reported at 9:30 UTC on 21 March. TEPCO then ordered an evacuation of plant personnel, though workers returned as of 00:00 UTC 22 March.

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 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. Spraying from trucks continued on 20 March. 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.

Unit 4

All fuel from Unit 4 had been removed from the reactor core for routine maintenance before the earthquake and placed into the spent fuel pool. The building's outer shell was damaged on 14 March, and there have been two reported fires - possibly including one in the area of the spent fuel pool on 15 March - that were extinguished spontaneously.

Authorities remain concerned about the condition of the spent fuel pool, and Japanese Self Defence Forces began spraying water into the building on 20 March. As of 8:17 UTC on 22 March, a concrete pump was pumping water into the spent fuel pool at a rate of 50 tonnes per hour. The reported plan was to pump water at this rate for 3 hours.

On 18 March, Japan assigned an INES rating of 3 to this site.

Units 5 and 6

Shut down for routine maintenance before the earthquake, both reactors achieved cold shutdown on 20 March. The reactors are now in a safe mode, with cooling systems stable and under control, and with low temperature and pressure within the reactor.

Instrumentation from both spent fuel pools had shown gradually increasing temperatures over the past few days. Officials configured two diesel generators at Unit 6 to power cooling and fresh-water replenishment systems in the spent fuel pools and cores of Units 5 and 6. As of 20 March, temperatures in both pools had decreased significantly. /p>

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.

…