Interesting article on nuclear reactor situation

[FourScore]

Battle to stabilise earthquake reactors
12 March 2011
UPDATE 11: 4.26 pm GMT





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 on site did not damage containment. Sea water injection was started but then paused after a tsunami warning.

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).

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...

http://www.world-nuclear-news.org/RS_Battle_to_stabilise_earthquake_reactors_1203111.html

[ananda]

1. You know this situation is very critical ...

... when they talk about all the makeshift ideas and juryrigging going on.

I mean, iodine tablets, sea water for cooling, boric acid -- come on, boric
acid to contain a meltdown!?! How safe would you feel?

[Sirveri]

2. boric acid is used to control neutron reactivity to prevent a restart from a core geometry change.

[roamer65]

4. Geometry change...as in a core that's in a partial meltdown?

That would constitute a geometry change I would bet.

[Sirveri]

5. There are several reasons, that being one of them yes.

Could be from an ejected control rod, stuck control rod, Fuel element failure with control rod obstruction, or for other reasons.

In this case the rods were likely fully inserted, and they injected to guarantee a shutdown. It could have been due to a fuel element failure, but it could also have simply been a precautionary issue.

[Warpy]

3. Iodine tablets prevent one of the more common cancers

after radiation exposure, but don't think of taking them here, we won't need them.

As for jury rigging, with your generators flooded out, no electricity and no way to keep water circulating via pump, dumping sea water into the overheated pile of fuel seems like a good idea.

Unfortunately, it was so hot that electrolysis occurred, splitting the hydrogen and oxygen forming the water apart and into an explosive mixture. Film of the explosion shows a nearly transparent but visible flame shooting straight up over 1000 feet from the top of the plant, typical of a hydrogen explosion. Then the walls collapsed and the dust arose. Video is on the BBC front page.

Likely the fuel and control rods have melted together into a useless mass. Eventually it will cool, but that particular plant is done for. There is nothing to do but encase it and post skull and crossbones signs on it.

[Sirveri]

6. Iodine functions by front loading the thyroid to prevent future Iodine uptake.

Basically you put a ton of Iodine in your body, your thyroid gobbles it all up, and then if you're exposed to radio iodine your thyroid won't grab it because it's already full. I agree though, no need for it in America, it should take a few days for any of the air there to reach us, and we'll have a better picture of what's going on then.

In this case it's possible for the hydrogen to have degassed from the coolant itself. They typically add hydrogen as an oxygen scavenger in plants.

[Warpy]

8. You're right, and broken down from a reaction

with the coating on the control rods + extreme heat.

However, that explosion really was a pretty obvious hydrogen explosion. The dust cloud was just the aftermath of having the roof collapse afterward.

[Junkdrawer]

7. What exploded if the Primary Containment didn't? And what was the mechanism....

of the explosion?

I'm having a hard time accepting Edano assurances.

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.