Less than 60degrees Celsius at plant fuel pools

[FBaggins]

Japan's Defense Ministry says that the temperature of spent fuel rod pools in 2 reactors of a seriously damaged nuclear plant has fallen below 60 degrees Celsius. The Ministry has been using helicopters to take infrared surveys of the surface temperatures of facilities at the Fukushima Daiichi Nuclear Power Plant since Saturday. The 3rd survey was done for half an hour from around 9 AM on Wednesday.

According to the Ministry, the surface temperature of the spent fuel rod pool at the No. 3 reactor was 57 degrees Celsius. The rod pool at the No. 4 reactor was recorded at 22 degrees Celsius. The first infrared survey on Sunday found temperatures under 100 degrees Celsius in the same facilities. The surface temperature of the container vessel for the No. 3 reactor was 35 degrees Celsius, down from128 degrees on Sunday.

The surface temperatures of the buildings of all 6 reactors at the plant were below 40 degrees Celsius. The Defense Ministry says the effort to cool the spent nuclear fuel rod pools contributed to the temperature falls.

It was revealed on Wednesday that the temperature of the core in the No. 1 reactor had reached about 400 degrees Celsius. The ministry says the surface temperature of the building housing the reactor was 38 degrees on Wednesday, as observed by aerial survey.


http://www3.nhk.or.jp/daily/english/24_05.html

[panader0]

1. I'm hopeful that they are getting a handle on this

[BeFree]

2. If we survive...

....it will make for an interesting movie.

[Buzz Clik]

4. I don't think that the survival of the human race is an issue here.

I have no doubt, though, that someone will make a really dumb movie based on this incident.

[Buzz Clik]

3. Perhaps the fuel rods have melted their way beneath the earth's mantle.

... leaving behind a scab of cooled -- though once molten -- rock.

Out of sight, out of mind.

[Sonoman]

5. Yeah, isn't that one hell of a lot of water to cool that quickly?

Especially if there were still 'hot' rods exposed to the cooling water.

I read, somewhere, where the rods could actually 'melt' downwards.

Sonoman

[FBaggins]

6. I wouldn't assume that a fixed volume of water is cooling.

I'd say that they've set up a system with the effect of "circulation".

Instead of pumping out hot water and cooling it before pumping it back in... they're pumping in cold water and the warmer water is either overflowing the pool or (more likely) leaking out. The effect is largely the same.

The real question at this point is how deep that pool is.

[Statistical]

8. Here are specs on spent fuel pond in GE MK I.

The fuel pond gate leads to the space above the reactor core. That space is flooded when refueling to create one large "pond" which covers both the spent & new fuel and the reactor itself. This allows fuel to be transfered between pond and reactor while keeping fuel under water the entire time.

Larger diagram showing relationship of pond and reactor head.



Accroding to UCS (I have no reason to doubt it). The overall volume of the ponds are:

"The pools at Units 2, 3, 4, and 5 all have a volume of 1,425 cubic meters, with dimensions of 12.2m x 9.9m x 11.8m deep. The Unit 1 pool is somewhat smaller (1,020 cubic meters) and the Unit 6 pool slightly larger (1,497 cubic meters)."

[FBaggins]

9. That's the specs on an undamaged unit.

I haven't seen anything yet that indicates how deep the effective portion of the pool is at this point.

But yeah, I posted a thread a few days ago that speculated that seals around the gates may have been compromised with the lack of power.

[Statistical]

7. Not really.

Water is an effective heat transfer mechanism. Spent fuel isn't that "hot" normally. Spent fuel cooling pond water is usually only warm. Thermal output of spent fuel decays rapidly. Water isn't making the heat "go away" like putting out a Forrest fire instead water is simply TRANSFERRING THAT heat. Much like radiator in your car works. The water in your radiation can't prevent the creation of thermal energy it can only move it. It moves it from a relatively small space (the spent fuel / your car engine) to a relatively large space (surface of cooling pond / radiator in your car).

The issue was the ponds were out of water. Air is not good at transferring heat. The spent fuel are continually generating thermal energy and that without an effective method to TRANSFER that energy away from the spent fuel the temp will continue to rise.

You can't reduce the thermal output of the spent fuel. It goes down on its own and according to its own timeline. So it isn't like a fire that you can put out. All you can do is ensure that thermal energy is transfered away from the spent fuel.

Temperature of a system is the difference between energy in and energy out. Energy in is nuclear decay without water energy out drops to nearly 0 and you see temps rise.

Thermal conductivity of water is 0.54 vs air which is 0.02. So all intents and purposes for the amount of thermal energy we are dealing with here air might as well be 0.