Nuclear experts (or anyone with more knowledge than I (everyone))?

I'm curious if the use of cryogenic coolers has been investigated for situations such as they face at Fukushima. I realize that direct injection of liquid nitrogen would be ill-advised, possible resulting in a crack of the reactor vessel due to extreme temperature differences, but it would seem some type of heat exchanger might be constructed on the spot instead of the last resort - pumping seawater into the reactor, which I've heard will also damage the reactor in any event.

The presence of LN2 might also offer the side benefit of lowering the oxygen content of its environment, making for a less explosive situation.

Oh, and I realize that a cryo cooler would also require a fairly significant amount of energy to operate, so maybe it's a Catch-22.

They could never be trusted after the stress they've been through.

Just curious whether cryocooling might be a solution to the immediate issue of preventing a meltdown.

Even the ones that were shut down for maintenance at the time would probably need months of inspection/repair before they could be used, and they aren't going to have anyone available to do that until they've spent months investigating what happened/is happening.

We're talking about a reactor core that, even with
chain-reaction fission stopped, is still producing
an enormous amount of heat through radioactive decay.

I read yesterday that a just-shut-down core still
produces about 6% of the heat of an active core so
if the reactor was rated at (say) 1.5 gigawatts of
thermal output, it would still be producing 90 megawatts
of heat.

That's a lot of heat and is far in excess of what any
cryogenic cooler is capable of. And they're powered
electrically and one of the big problems is that there
isn't much electricity available at or near these
plants right now.

The reason we typically use water as the heat transfer
medium is that water can carry a lot of heat and water,
even very high quality water, is readily available in
enormous quantities; by comparison, cryogenic fluids
are much less common.

Tesha

IDemo once again fails to save the planet.

I read yesterday that a just-shut-down core still
produces about 6% of the heat of an active core so
if the reactor was rated at (say) 1.5 gigawatts of
thermal output, it would still be producing 90 megawatts
of heat.

That's a lot of heat and is far in excess of what any
cryogenic cooler is capable of. And they're powered
electrically and one of the big problems is that there
isn't much electricity available at or near these
plants right now.
=========================================

You are exactly correct. Each of those reactor plants has an electric
output as follows: 460 Mw for Unit 1, and 784 Mw for the other three in
the set of four. < the 2 newest units are 784 and 1100 Mw >. That's the
electric output. Since the Rankine steam cycle is only about 30-40% efficient,
the thermal output of those plants at full power is about 1.3 Gw for Unit 1,
and 2.4 Gw for the others. Right after shutdown, the heat load due to
radioactivity is about 6% to 7% of the thermal reactor power pre-shutdown.
So 90 Mw is the correct number for Unit 1, and something like 150 Mw is
appropriate for Unit 3.

There's no cryogenic system that can handle that type of heat load. Additionally,
you want lots of heat removal capacity, meaning you want the coolant to have a
high heat capacity. Heat capacity is the product of specific heat and density.

There you have a real problem. These cryogenic cooling systems use gases as the
coolant. The density of a gas is about 1/1,000-th that of liquid water. So even
though the gases are very cold, that doesn't make up for the fact that they are
also 1/1,000-th the density.

You also need some type of pump to get those gases into the reactor. In order to
prevent as much boiling of the coolant as possible, the pressure in those systems
would still be kept pretty high. A BWR normally runs at about 1,000 psi. A PWR
normally runs at about 2,000 psi. So you need a pump to get the coolant gas into
the high pressure of the reactor system.

Cryogenics is neat and whiz bang, but it doesn't buy you enough heat removal capacity
to tackle a problem the size of cooling a power reactor.

PamW

But there wasn't a 8.9 earthquake that destroyed the infrastructure surrounding the plant.

...blocks that "moderated" their nuclear pile.
Liquid nitrogen sounds like a pretty good idea
there because not only would it remove some heat,
the gaseous nitrogen that resulted when the liquid
nitrogen boiled-off would displace the oxygen-
bearing air and help quench the fire.

Tesha

what they will do with the remains is the problem they are facing.

Being made-of or at least clad-in mostly high-quality
stainless steels, nuclear plants *ARE* somewhat
corrosion-resistant. I suspect the operators and
regulators of the plant would assess the aftermath
on a component-by-component basis using appropriate
testing methods (chemical, ultrasound, X-ray, magna-
flux, etc.) and decide what needed to be scrapped
and what could be reconditioned and returned to
service.

But right now, what to do in the aftermath still
sounds like the least of their problems.

Tesha

presumably to ensure that the plastic melted and adhered to any fuel pellets that have fallen to the base of the vessel.

then I thought why would they do that? does bacon have some power against radiation?

then I reread it. I gotta slow down.

Then again, maybe not.