Radiation levels hit new high at Fukushima Daiichi

16 March 2011

Tokyo Electric Power Company temporarily evacuated workers from the Fukushima nuclear power station early on 16 March as radiation levels hit a new high at reactor 3. White fumes have been seen coming from reactor 3 and the operator fears that there has been damage to the suppression chamber. A fire also occurred overnight at reactor 4.

Reactor-by-reactor, system-by-system summary from JAIF on 16 March
Reactor-by-reactor, system-by-system summary from JAIF on 16 March; yellow indicates abnormal/unstable; red means damaged/nonfunctional/unsafe

In a statement Tepco said that at approximately 6:00am “an abnormal noise began emanating from nearby the pressure suppression chamber of Fukushima Daiichi Power Station. Given that the pressure within this chamber had decreased, it was believed that this was an indication that an abnormality had arisen.”

In his latest briefing chief cabinet secretary Yukio Edano reported that white fumes had been observed coming from unit 3. He said that, as with unit 2, it is possible that radioactively contaminated steam is being released from the containment vessel.

In the early hours of yesterday morning (15 March) a hydrogen explosion at reactor 2 caused damage to the suppression chamber, which holds water and steam released from the reactor core. In its latest update on 16 March Tepco said the containment vessel at reactor 2 showed “no significant change.”

On 15 March Tepco also reported damage to the fourth floor rooftop area of the number 4 reactor building, where a fire burned for approximately two hours, according to the International Atomic Energy Agency.

Edano said in a statement that the authorities presume the fire started after a hydrogen explosion (with the hydrogen being generated by heating of the spent nuclear fuel). Later the Nuclear Energy Institute said that Tepco reported the cause as an oil leak in one of the reactor cooling pumps.

At 5:45am, 16 March a fire reignited at reactor 4 of the Fukushima Daiichi plant. It was extinguished after 90 minutes, according to reports from the IAEA.

Yesterday non-essential staff were evacuated from the Fukushima Daiichi site, with just fifty remaining to continue seawater injection into reactors 1-3. Radiation levels reached 400 mSv/hr between unit 3 and unit 4 and 30 mSv/hr between unit 2 and unit 3 at 10:22am on 15 March. Higher levels were measured next to reactor 3 today and Tepco made the decision temporarily transfer employees and other workers to a “safe place” while water injection operations were underway. Press reports indicate that workers have now returned.

Plant operators were considering the removal of panels from units 5 and 6 reactor buildings to prevent a possible build-up of hydrogen in the future. It was a build-up of hydrogen at units 1, 2 and 3 that led to explosions at the Daiichi facilities in recent days.

Concern also remains for units 5 and 6 where water temperature in the spent fuel pools have been increasing. Edano said that that it would be dealt with in a “proactive manner”. Reports from Japanese authorities to the IAEA show that the water level in unit 5 had decreased to 201 cm above the top of the fuel by 12:00 UTC on 15 March, representing a 40cm decrease in five hours. Officials at the plant were planning to use an operational diesel generator in unit 6 to supply water to unit 5, the IAEA reported.

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