On vacation, presumably you would use a water heater that allowed for recirculating in cold water if it got over temp, presumably you could even open a radiator loop for that. The goal is to have something that is thermally stable sitting out in the open air and still can warm water to a usefully warm temperature.

There was a discussion of this sort of thing in the papers on the pebble bed reactor (that reactor uses encased fuel "pebbles" and one question came up with what you do with the "used up" ones.) It has come up off and on both at conferences and in discussion forums.

if there's any water left in that water heater after a couple hours and it didnt explode from vapor overpressure, you'll painfully die of acute radiation sickness.

that's the best case scenario.

You over estimate the decay heat in a kg of spent fuel. According to here [1], a 1GW (1000MW) plant uses 100 Metric tons of fuel, so 1 kg is responsible for 1G/100K or 10Kwatts and the decay heat of spent fuel is .1% of its nominal power level so 10K * .001 or 10 watts. If you dump 10 watts into your water heater it will get hotter and depending on the heat insulation of the tank it might even get to boiling. Although typically I would expect a tank to lose close to 10W into the ambient air once the water was at temperature.

[1] http://www.nucleartourist.com/basics/hlwaste.htm

No argument, though it's hard to envision a scenario where [1] is not a predetermined eventuality for any setup that would be laughably inadequate or economically impractical.

[1] https://en.m.wikipedia.org/wiki/Fukushima_Daiichi_units_4,_5...

It doesn't follow, fuel (whether spent or not), is density and dissipation question. Each kg of fuel is generating heat, so more fuel in a smaller space means more heat in a smaller space. Fukishima's spent fuel ponds had both spent and fresh fuel in them (reactor 4 was undergoing maintenance) and there was a lot of it. Spread that fuel out across say a hectare pool of water that is 5 meters deep and it stays out of trouble.

One disposal plan called for mixing the fuel with silica to create glass bricks. By spreading the fuel mixture to a density that was low enough to allow the ambient air to cool it, the bricks are shelf stable for thousands of years and not a radiation hazard (less of a risk than even natural uranium deposits you might come across).

Many disposal plans were like this, encapsulate the spent fuel into a container that withstands (and blocks) the radiation while conducting enough heat to avoid changing the properties of the material over the lifetime of its storage. Glass and austenitic stainless are both good candidates for that material.

This does not really change the conversation.

The fact that spent nuclear fuel must be kept in water at all until it is sufficiently decayed to be put into dry storage still safely away from humans means it is by definition not fail safe. Water evaporates and if you lose the ability to dissipate heat or absorb ionizing radiation, "you're in deep shit" would be a colossal understatement. How comfortable would you be that something on your property or in your home is one water outage or tank failure away from irradiating your family and probably a bunch of your neighbors. I imagine the hazmat team won't be happy to be invited to your housewarming either.

If it requires cooling or radiation-blocking-immersion to be safe, it absolutely has to be monitored by trained personnel 24x7 who can also immediately and reliably take necessary measures when something goes wrong. Anything less than this is a non-starter. Nuclear reactors work because they centralize risk to where it can be managed by a team of knowledgeable people; A 1GW reactor does not have the same risk profile as 1000 dispersed 1MW reactors.

But that was my point, spent fuel doesn't have to be kept in water at all, if it is sufficiently dispersed. Take a spent fuel assembly remove each of the fuel rods and lay them down on the ground and you're done caveat two things, one they emit alpha, beta, and some gamma radiation and two they warm their surroundings. So there always exists a solution to the equation of heat generated over time = heat absorbed by ambient air keep the total temperature rise below that of the safe temperature of the cladding.

If you lay a spent rod out on the ground in the air, it may glow (would depend on the amount of material in a single rod) and you wouldn't want to approach it without protection (again more material more radiation) but it would be fine.

The reason people put these things in water is two fold, one is that water is a great transporter of heat and you can generate almost an arbitrary amount of heat in a small space if you have enough water flow to carry it away (ask any highend gamer PC aficionado :-)) and water absorbs neutrons, which if they were not caught and hit another fissile atom nearby slowly enough might spit it, or a non-fissile atom might become an unstable nucleotide (which is going to eventually emit an alpha or beta particle)

If the material is clad in a neutron opaque material and can transfer the latent heat to the surrounding atmosphere or fluid at a rate that keeps the system temperature under the breakdown temperature of the containment, then it will be stable "forever".

Yes, it takes a year or two for the short lived nucleotides in a fuel rod pulled from a reactor to decay, but once it has, you can safely store this stuff.

In terms of why we haven't, most of the issues around storing high level nuclear waste arise because third parties do not want to encapsulate permanently this material, because doing so would make it uneconomical to recover. And in that calculus they know its "easier" to reprocess spent fuel for bomb grade uranium and plutonium than it is to build a breeder reactor to make it.

> it might even get to boiling

if it can boil water, can't it be used to generate electricity? What makes it "spent"?

You could, but it would be less than 10W of electricity, so not enough to power a lightbulb. The water tank is insulated, so the water just heats up slowly until it reaches boiling point. That doesn't mean it's a powerful heat source.

So basically if you use up all the hot water in your shower you are going to be in hot water!

Ah I see, so it's about the rate of heating more than the amount of heat it can potentially generate. That makes sense, thanks.

I don't think the energy output is linear like that, don't you need to account for cross-sectional area?

This sounds like something out of "Chemicals I won't work with."

yeah, also fun: https://en.m.wikipedia.org/wiki/Demon_core

Interesting read. Can someone explain why they were performing these experiments in blue jeans and shirts?

It was the 1940's and nuclear material safety wasn't as critical an issue as it is now.

I'd hope there would be only alpha and betta emitters on the ball. Who would ever transport neutron and gamma radiation out of confinement?

I would also hope it would be dimensioned for radiation cooling when over 100°C.

Still wouldn't want people to have those at home anywhere near me. But it's mostly because of misuse, not because of operational dangers.

Slow neutrons aren't so bad. May as well get used to them, as they will be around for a while.

I like the idea of having to type 6 numbers (yes those numbers!) into a computer to release the pressure.

er... which numbers? can someone expand on this?

4 8 15 16 23 and 42

Lost. Old TV show. Netflix maybe?

I think he means the 000000 that the USAF set the password to for launching the LGM-30 Minuteman ICBM. For expediency, apparently.

That was eight zeroes, not six. Two more bits of entropy!

Ah, 8 of them.

I bet that made it some much more secure! /s

> Twelve milkmen IS theoretically possible. Thirteen is silly.

From "Freaked" (1993)

You really consider a TV programme that ran from 2004 to 2010 old?

I'm the old dude (42) who works in a team with a bunch of milennials. It is humbling and bizarre to realize that they were kids when 9/11 happened, when Lost ran, when George W. Bush was president, when Java 5 was released, Ruby on Rails became trendy, all events that occurred when I was already old and even having kids.

Ugh

Wow, that hit me right in the feeling-old-shin. I gave up on it between season 2 and 3, thinking I'd get back to it sometime. Didn't realize it's become an "old TV show", but I suppose you're right.

"That's amazing! I've got the same combination on my luggage!"

I think I might start buying lotto tickets with those numbers.

By law, all water heaters need a regulator pressure valve. (Before this federal requirement; some people had rocket in their garage. Middle of the night a water heater would go through the roof, if the homeowner was lucky.). In this case, I would want four regulators, on my nuclear hydronic heater.

laws have to ruin all the fun. hopefully there aren't any pesky laws preventing spent nuclear fuel from being used for DIY residential heating.

Yeah, we should definitely let the free market determine the natural safety appetite of citizens ;)

Hmm, I wonder if you could use one of those in place of a pahr splah.

Bah, Philistines. Don't you people ever google unrecognized terms?