HN Explorer

Ask HN: Why can't nuclear waste be launched into the sun?

28 points by jamestimmins ↗ HN
My understanding is that nuclear waste is relatively small in volume, yet storage is problematic. If companies like SpaceX succeed, and the price of launching cargo into space falls by another order of magnitude or two, is is either possible or feasible to launch the waste out of Earth's orbit, either into deep space or at the sun?

I can think of a few reasons this might be risky or impossible:

    1. The risk of launching nuclear waste is too high, given the possibility of a failed launch spreading the waste in our atmosphere.
    2. Even with an order of magnitude decrease in launch prices, it is still prohibitively expensive.
    3. For engineering reasons, it's nearly impossible to launch a rocket at the sun.
If nuclear rockets or reactors are built in space, would this be a possible way of handling nuclear waste from reactors already in space?

37 comments

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chovyfu
or our trash. always wondered this. its probably cost prohibitive is the general answer.
tartoran
No, our trash should be recycled as much as possible and where not possible try to avoid those materials. Plastic is one of them.
nexuist
Trash is never really trash - you can always do something with those resources, the only problem is that nobody wants to do something with it now.

You can imagine it might actually be pretty profitable to buy landfills when you're, say, a plastics manufacturing / distributing company, because the land is super cheap and you can literally dig plastic from the ground to sell to others.

hindsightbias
Finding the most expensive solution to a problem sometimes works for DoD or NASA. But nuclear just isnt sexy enough.
scribu
"For a spacecraft to launch toward the sun, it must accelerate to nearly match the Earth’s velocity—in the opposite direction."

Source: https://www.theatlantic.com/science/archive/2018/08/parker-s...

> If nuclear rockets or reactors are built in space, would this be a possible way of handling nuclear waste from reactors already in space?

If you're not already falling towards the Sun, it must mean you're in some sort of orbit around it. So you'd still need to cancel that out.

dgrin91
To make it a bit more explicit - this requires a LOT of energy. Much more than is typically used on a regular space launch. The closest man made object to the sun is the Parker solar probe and it required a very large rocket AND multiple planetary assists (meaning the planets have to be lined up just right, which doesn't happen often), and with all that it _still_ doesn't go into the sun, just close to it.
db48x
Not only is the Sun the most expensive place in the solar system to deliver cargo to, it's also a really stupid idea to throw away nuclear waste. What we call waste today is really just fuel that we have extracted about 2% of the available energy from. The other 98% of the energy is still in there, waiting for us to decide to use it. The only reason we don't use that energy is that we didn't build reactors that can use it, and these days it's basically impossible to build new reactors. Too much politics, too many rules, too much NIMBY.
skitout
And way too expensive for classic reactor [1], while a reactor running with nuclear waste as fuel would probably be even more expensive as there are no one running...

[1] https://www.lazard.com/media/451086/lazards-levelized-cost-o...

db48x
Yes, too much NIMBY means too much cost. You can't really move a nuclear power plant away from your neighbors and into a desert because you need ample cooling water.
sxp
You should play https://www.kerbalspaceprogram.com/ to learn the mathematics of orbital dynamics required to launch something into the sun. It's really hard which is why many of our solar system probes need to bounce off other planets (aka "gravity assist") to get close to the sun.

The math might change once we get a space elevator and a solar sail since it would be cheaper to get things into orbit and then parachute them into the sun.

Another idea would be to bury it into a really deep hole (https://en.wikipedia.org/wiki/Deep_borehole_disposal) or a part of the tectonic plates that would quickly take it into the Earth's core (https://en.wikipedia.org/wiki/Ocean_floor_disposal).

tjpnz
I never learned any math from KSP (maybe I'm just playing it wrong?) but it did impart me with an intuitive understanding of how orbital mechanics work. That would be enough for most to understand why it would be impractical.
rraghur
I was in the same boat for a long time and mike aben.'s videos on youtube helped a lot for the math to click Once it did though, it opened a while new level in mission planning gameplay because now the challenge was to build the most efficient rockets & probes..

Seriously, give it a go and you'd probably have the same experience!

nabla9
Very popular question.

The short answer is: Counterintuitively it would take less energy to launch a spacecraft to another star than our own sun

As for why not into the space in general:

Risk of rockets failing. Lancing probes with small nuclear batteries is controversial. Think about launching tens of tons of nuclear waste. Almost 100,000 tonnes of nuclear waste is produced per year. That's clearly too much to launch.

If we would use SpaceX Falcon Heavy to launch only the highly radioactive waste )12,000 tons per year) for $2,500 per kg. It would cost $30 billion per year and 240 Falcon Heavy launches per year. Some of them will fall down, explode etc. and that must be dealt with.

----

https://www.popularmechanics.com/space/rockets/a21896/why-we...

https://www.forbes.com/sites/startswithabang/2019/09/20/this...

https://www.universetoday.com/133317/can-we-launch-nuclear-w...

https://astronomy.com/news/2016/07/heres-why-we-cant-just-ro...

nexuist
> Risk of rockets failing

The thing is, we transport nuclear waste over sea or air all the time, don't we? I believe the spent fuel is put into "casks" which is then loaded onto ships or jumbo jets and flown around the world.

Planes crash and ships sink, but we judge the risk (with proper pre-cautions) to be low enough when transporting radioactive waste. To me this shows that people generally accept transporting nuclear waste when the danger of catastrophe is low enough - importantly this signals that the risk only has to be low enough, it doesn't actually have to be 0.

Presumably as rocket technology advances we will eventually enter a stage similar to that in air travel, where the risk of a crash is measured in 1-per-billions rather than 1-per-hundreds or 1-per-dozens.

At that point, would we accept launching radioactive waste into space?

db48x
Don't forget that those casks are really heavy. If you launch the "waste" into space in them you'll be launching a lot more mass than just the 30kt. I don't know the exact ratio between cask mass and waste mass, but it could easily be 10:1.

Also, I'll repeat that throwing away valuable nuclear material just because it's called a "waste" product is stupid. Paying a lot of money to throw it into space is even dumber.

SwiftyBug
Are there any practical uses for nuclear waste?
foxyv
I think they are referring to fast reactors (Referring to the fast neutrons used to induce fission) that can burn high level nuclear waste from standard PWR plants as fuel.
nabla9
Some types of fresh nuclear fuel can be transported trough air, with limited amounts at the time.

Used nuclear fuel in those flasks are not transported trough air. Always by land or sea. On the sea they are transported in purpose-built ships.

Small amounts of highly radioactive nuclear fuel are transported trough air but they be in extremely secure type C containers that survive crash from cruising altitude. Creating similar containers that survive crash from space launch would make launching very expensive. Most of the payload would be just the container and only small amounts would be radioactive material.

It's 1000 times cheaper to recycle nuclear fuel make nuclear reactors that use nuclear waste than shoot it into space. France does it in La Hague. The rest can be buried into the ground.

qu-everything
Totally different, a space ship failling would mean tons of nuclear dust in the upper atmosphere, wich would mean radioactive material spreading everywhere in the world, poisonning everything.
jfengel
I'm a little baffled that the question is so perennial. You'd think it would start and end with "thousands of dollars per kilogram". Landfill fees are closer to "pennies per kilogram".

There's all kinds of technical reasons as well, and people love talking about space. But "five orders of magnitude in costs" seems like the conversation ends very abruptly.

jamestimmins
Just speaking as OP, I think it's bc of the little information that gets into the public about nuclear science in general, much of it is about the cost and dangers of nuclear waste. I have the impression of this thing that has to be maintained by burying it under a mountain in North Dakota for the next 50,000 years.

So while 5 orders of magnitude makes the financial case clear, I don't have a good idea if the risks of keeping it around are potentially 6-7 orders of magnitude greater than getting rid of it.

jamestimmins
This is pretty fascinating. I naively assumed that if you got something outside of Earth's orbit and stopped pushing it, eventually the Sun's gravity would take it from there.

Regarding price, that's quite a bit more in volume and cost than I realized. Thanks for the info!

simonblack
I once suggested that we put it into orbit, probably around the Sun. That meant it was far enough away not be harmful, but close enough that when conditions were right, it could be recycled into usable resources.
andrey_utkin
Turning nuclear waste into nuclear space debris!
simonblack
nuclear asteroids <grin>

Put into stable orbit around the Sun both gets it away from Earth and also available if in 800 years we find a good use for it to be recycled. If, on the other hand, there's never a recycling use found for it, it can safely decay for a few thousand years till it's harmless.

It's probably cheaper overall to put it into stable solar orbit than trying to dispose of it safely on Earth. And a stable orbit means that it's location can be accurately determined for thousands of years. Possibly even specifically locating "Nuclear power waste in this sector, medical nuclear waste in that sector, excess plutonium in that sector, ..." etc.

To day's deserts may be tomorrow's urban areas. Imagine how much it would cost to safely clean up a huge area that's been contaminated by nuclear waste.

(There's plenty of evidence of the cost of cleaning up old nuclear test sites. https://www.nytimes.com/1990/07/04/us/cost-of-cleanup-at-nuc...)

Back when the world wanted kerosene for lamps, the 'rubbish' petrol/gasoline was discarded for many years. That petrol would be very valuable today, but it's been lost.

known
May be possible in the longer run when we have appropriate cost-benefit-analysis
ALittleLight
Storing nuclear waste isn't really a problem, we have a lot of ground to bury it in, and, as you say, it's relatively small. One way to think about it is that the nuclear fuel is all buried in the ground before we use it, so burying the waste (or using it in a different reactor) seems perfectly reasonable.
skitout
Nuclear fuel is not as radioactive than nuclear waste, putting it in the ground has a lot of challenge and (long term) risk
himinlomax
The most promising scheme for dumping waste is deep coring. Previous schemes involved digging shallow burial sites, 100 m or 200 m deep. This is not safe in the medium term, as ground water could easily seep through in the case of geological events. But if you drill a 2000 m hole and cover it back up, there's absolutely no chance of the material coming back up in any way (as long as the site is not the worst.)
logotype
Why not the other way around? Drill into the earths core and simply dump it there.
girishso
The problem is heat. The deepest hole we have built till now is about 12kms, which is nowhere near the earth's core.
happy_path
Side question, and what about sending nuclear waste to a volcano?
Someone
The volcano might explode a day/month/year/decade/century later.
nodelessness
And now you have radioactive magma. Rock mixed with radioactive nuclear residue elements. It doesn't "disappear". It is not being burnt out of existence. It is still radioactive at a atomic level.
qu-everything
great! Now if there is an eruption, we have radioactive ashes in the atmosphere. perfect!
alkonaut
Yes, all of the above.

2 and 3 are almost the same thing with “difficult” and “expensive” being closely related.

notaspecialist
We should hoard that like the gem it is. Higher atomic-complex material that is not common like hydrogen can be useful for the future when we learn how to artificially increase the neutron count in a stable method.