Reactor cooling efforts missing mark: B.C. expert (Pssst… try using longer cables, and hovering)

[OKIsItJustMe]

http://www.cbc.ca/news/canada/british-columbia/story/2011/03/18/bc-japan-reactors-water-buckets.html

Reactor cooling efforts missing mark: B.C. expert

CBC News
Posted: Mar 19, 2011 10:34 AM PT

A Delta, B.C., company says it's trying to help correct mistakes being made in the Japanese efforts to control the growing heat at Japan's damaged nuclear reactors.

SEI Industries Ltd. manufactures the helicopter buckets that have been used to dump cooling water on nuclear power stations at the Fukushima Daichi reactors.

…

Arney said the helicopters are using only seven-metre to ten-metre lines strung from their aircraft and are travelling too quickly over their targets.

"To be more effective is to use a <60-metre> line, as used in North America and to slow down to a hover," Arney said. "Get that bucket right over to the hole in the roof over the reactor and let the whole load go in."

…

[FBaggins]

1. They can't hover.

There's a common mistake that people here are making. They misunderstand the difference between "radiation" and "radioactive materials".

If the pools are dry or even low (even if the rods are covered by a couple feet), there can be an incredible amount of radiation released. But it's all going to go (essentially) straight up. That's not going to "plume" or spread... it's just going to keep going into space unless it hits something. The one place you don't want to hang around is somewhere over the lip of one of those pools.

But yeah... a longer line would make that a little easier.


It doesn't appear to be a big concern, however, since the newer fire equipment seems to be getting lots of water on target now.

[OKIsItJustMe]

2. Inverse square law

Twice as high above the radiation source means 1 fourth the dose.
http://en.wikipedia.org/wiki/Inverse-square_law

[LunaSea]

3. Dropping it all at once might be like dropping a load of bricks

You don't want to do more damage in there.
I suspect they dropped it in that manner for good reason.

[OKIsItJustMe]

4. How close can you get the bucket to the target?

Essentially draining the bucket directly into the target should be much less damaging then dropping water from a greater height with a horizontal velocity.

[FBaggins]

5. True enough... but the dose is more than four times too high.

If it was necessary, I'd say go for it. It probably won't kill them...

...but it doesn't appear necessary. The pool most (IMO) in need has part of a roof over it and the fire trucks look like they can get water on target for hours at a time.

[OKIsItJustMe]

6. Of course, we're not talking about a factor of 4 here

The expert was not suggesting they use cables twice as long, but six or more times as long.

(I was merely summarizing the inverse-square law.)

[FBaggins]

7. Of course.

I'm just saying... if you get a lethal dose in 16 seconds standing at the side of the pool with six feet of water in it (so the fuel is, say, 30 ft below you)... I don't think that I would want to be 300 feet above the pool. It may "only" be 1/100th of the dose, but that means that half an hour would kill you.

You've got to fly in slow enough and hover long enough to get the bucket steady over the target. Even if that's 30 seconds (and I bet it's longer), I don't want to be the pilot. Just a handful of trips would put you over the annual dose.

That's based on just memory of what I read about the dose with low water... but it's also possible that there's LESS than six feet of water over the rods.

[OKIsItJustMe]

8. And of course, water is a radiation shield

(That's part of the reason for wanting to get it on the rods.)

The more successful they are in dropping their radiation shield onto the rods, the lesser the dose for the next approach, and more effective approaches also mean that fewer approaches will need to be made (further reducing net exposure.)