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Curious layman

Nuclear ‘Power Balls’ May Make Meltdowns a Thing of the Past

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Interesting, but they mentioned Fukushima and implied the meltdown was because of the operating temperature of the reactor while it was running, and that wasn't the issue. It was the decay heat while the reactor was shut down. Pumps didn't run to remove the heat, and that's what caused the high temperatures.

The discussion of the operating temperature is moot. It's the temperature of the core after a loss of coolant that matters, and it can go much higher than the 2000 ºF they mention

"TEPCO estimates the nuclear fuel was exposed to the air less than five hours after the earthquake struck. Fuel rods melted away rapidly as the temperature inside the core reached 2,800 °C within six hours." 

https://en.wikipedia.org/wiki/Fukushima_Daiichi_nuclear_disaster_(Unit_1_Reactor)

2800 ºC is over 5000 ºF. Oops.

That's the problem that needs to be addressed.  

 

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Posted (edited)

Isn't this a rehash of the pebble bed idea of a few years ago....they were grape sized as I recall, with similar coating of graphite or some other stabilizing element. Why so tiny?  That seems to be a danger in itself, so small it would be hard to keep track of each particle's state of depletion and then to manipulate during refuelings

Edited by hoola

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I find this interesting "fuel is made from a mixture of low enriched uranium and oxygen"
I wonder if the rest of the article is equally inaccurate.
"
Sell says. “It is physically impossible—as in, against the laws of physics—for triso to melt in a reactor,” says Sell"
The Titanic was unsinkable for the same reason.

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These two papers, Initial results from safety testing of US AGR-2 irradiation test fuel and Key results from irradiation and post-irradiation examination of AGR-1 UCO TRISO fuel,

report on Triso tests to 1,600o C and 1,700o C respectively, well below the crucial temperature of 2,800o C mentioned by @swansont I can find nothing reporting tests at higher temperatures.

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Imagine that, rather than rigid beads, these contained dots of nuclear material surrounded by a gas and then an elastic membrane. In that case, if the reactor got too hot the gas would expand and increase the distance between the dots. That would reduce the reaction rate and so the reactor would cool again.

You can achieve the same sort of effect by having a reactor that relies on  heavy water as the moderator as well as the coolant. If it gets too hot the heavy water boils off.

So it's sort of possible to make a reactor that can't overheat.

But I don't see anything here that would achieve that  outcome. It might be there, but they didn't mention it.


 

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12 hours ago, John Cuthber said:

Imagine that, rather than rigid beads, these contained dots of nuclear material surrounded by a gas and then an elastic membrane. In that case, if the reactor got too hot the gas would expand and increase the distance between the dots. That would reduce the reaction rate and so the reactor would cool again.

You can achieve the same sort of effect by having a reactor that relies on  heavy water as the moderator as well as the coolant. If it gets too hot the heavy water boils off.

So it's sort of possible to make a reactor that can't overheat.

But I don't see anything here that would achieve that  outcome. It might be there, but they didn't mention it.


 

Small water cooled + moderated pressurized water reactors act the same way - the water expands when heated, slowing the moderation down.

But none of that matters in a loss of coolant casualty. Safety is predicated on keeping the core covered, and in the worst accidents we’ve witnessed, the core did not remain covered.

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