World Nuclear News Forensic Analysis Of Events At Fukushima Nuclear Plant

Tyler Durden's picture

With much conflicting and biased news coming out of the mainstream media in its perfectly explainable attempt to prevent panic among the population, the World Nuclear News has released the best and most objective analysis of the events that have transpired and that have yet to transpire at Fukushima we have read to date.

Reactor overview:

Fukushima Daiichi

Unit 1
- 439 MWe BWR, 1971
- Automatically shut down
- Water level decreasing
- Pressure release implemented
- Explosion observed 

- Containment believed intact
- Seawater injection has started
- Radiation levels unchanged after
  explosion

Unit 2
- 760 MWe BWR, 1974
- Automatically shut down
- Water level lower but steady
- Preparations for pressure release

Unit 3
- 760 MWe BWR, 1976
- Automatically shut down
- Preparations for pressure release

Unit 4
- 760 MWe BWR, 1978
- Shut for periodic inspection

Unit 5
- 760 MWe BWR, 1978
- Shut for periodic inspection

Unit 6
- 1067 MWe BWR, 1979
- Shut for periodic inspection
 
Fukushima Daini 

Unit 1

- 1067 MWe BWR, 1982
- Automatically shut down
- Offsite power available
- Water level stable
- Preparations for pressure release

Unit 2
- 1067 MWe BWR, 1984
- Automatically shut down
- Offsite power available
- Water level stable
- Preparations for pressure release

Unit 3
- 1067 MWe BWR, 1985
- Automatically shut down
- Offsite power available
- Water level stable
- Preparations for pressure release

Unit 4
- 1067 MWe BWR, 1987
- Automatically shut down
- Offsite power available
- Water level stable
- Preparations for pressure release

From World Nuclear News.

Attention is focused on the Fukushima Daiichi and Daini
nuclear power plants as Japan struggles to cope in the aftermath of its
worst earthquake in recorded history. An explosion has been seen at the
site and seawater is now being injected to the plant.
 

Three of Fukushima Daiichi's six reactors were in operation when
yesterday's quake hit, at which point they shut down automatically and
commenced removal of residual heat with the help of emergency diesel
generators. These suddenly stopped about an hour later, and this has
been put down to tsunami flooding by the International Atomic Energy
Agency (IAEA).

The loss of the diesels led the plant owners Tokyo Electric Power Company (Tepco) to immediately notify the government of a technical emergency situation, which allows officials to take additional precautionary measures.

For many hours the primary focus of work at the site was to connect enough portable power modules to fully replace the diesels and enable the full operation of cooling systems.

Pressure and releases

Without enough power for cooling systems, decay heat from the reactor cores of units 1, 2 and 3 has gradually reduced coolant water levels through evaporation. The consequent increase in pressure in the coolant circuit can be managed via pressure release valves. However, this leads to an increase in pressure within the reactor building containment. Tepco has said that the pressure within the containment of Fukushima Daiichi 1 has reached around 840 kPa, compared to reference levels of 400 kPa.

The company has decided to manage this "for those units that cannot confirm certain levels of water injection" by means of a controlled release of air and water vapour to the atmosphere. Because this water has been through the reactor core, this would inevitably mean a certain release of radiation. The IAEA said this would be filtered to retain radiation within the containment. Tepco has confirmed it was in the process of relieving pressure at unit 1 while preparing to do the same for units 2 and 3

Explosion

Television cameras trained on the plant captured a dramatic explosion surrounding unit 1 at around 6pm. Amid a visible pressure release and a cloud of dust it was not possible to know the extent of the damage. The external building structure does not act as the containment, which is an airtight engineered boundary within. Chief cabinet secretary Yukio Edano appeared on television to clarify that the explosion had damaged the walls and roof of the reactor building but had not compromised the containment. 

Monitoring of Fukushima Daiichi 1 had previously shown an increase in radiation levels detected emerging from the plant via routes such as the exhaust stack and the discharge canal. Tepco have said that the amount of radioactive material such as iodine it is detecting have been increasing. The amount of radiation at the site boundary now exceeds a regulatory limit triggering another set of emergency precautions.

To protect the public from potential health effects of radioactive isotopes of iodine that could potentially be released, authorities are preparing to distribute tablets of non-radioactive potassium-iodide. This is quickly taken up by the body and its presence prevents the take-up of iodine should people be exposed to it.

The injection of seawater into the building started at 8.20pm and this will be followed by addition of boric acid, which is used to inhibit nuclear reactions.

Over the last several hours evacuation orders for local residents have been incrementally increased and now cover people living within 20 kilometres of the power plant.

Raised temperatures  

Meanwhile at adjacent Fukushima Daini, where four reactors have been shut down safely since the earthquake hit, Tepco has notified government of another emergency status. 

Unit 1's reactor core isolation cooling system had been operating normally, and this was later supplemented by a separate make-up water condensate system. However, the latter was lost at 5.32am local time when its suppression chamber reached 100ºC. This led Tepco to notify government of another technical emergency situation. 

Tepco has announced it has decided to prepare for controlled releases to ease pressure in the containments of all four units at Fukushima Daini.  

A three kilometre evacuation is in progress, with residents in a zone out to ten kilometres given notice of potential expansion.

Workers

A seriously injured worker was trapped within Fukushima Daiichi unit 1 in the crane operating console of the exhaust stack and is now confirmed to have died. Four workers were injured by the explosion at the same reactor and have been taken to hospital. A contractor was found unconscious and taken to hospital.

Two workers of a 'cooperative firm' were injured, said Tepco; one with a broken bone.

At Fukushima Daiini unit 3 one worker received a radiation dose of 106 mSv. This is comparable to levels deemed acceptable in emergency situations by some national nuclear safety regulators.

The whereabout of two Tepco workers remains unkonwn.

h/t Themos Mitsos