Why the sun is a poor dumping ground for nuclear waste (2010) • Hacker News Board

Re: Why the sun is a poor dumping ground for nuclear waste (2010)

#161

Post by lmm » Tue, Apr 14, 2015, 9:13 AM UTC

exDM69 wrote: post #151

dalke wrote: post #100

Earlier quoted context omitted.

While the solar wind gets stronger closer to the sun, it's an r-square law that balances the r-squared force of gravity. Fun fact: If a solar sail could be in a fixed position at Mercury orbit then it could also be in fixed position a Neptune orbit. Quoting from http://en.wikipedia.org/wiki/Solar_sail , the "total force exerted on an 800 by 800 meter solar sail, for example, is about 5 newtons (1.1 lbf) at Earth's di…

Your calculations seem sensible, but you're only talking about radial forces, ie. countering the "downward" force of gravity with "upward" thrust of a solar sail. But space flight maneuvers typically use tangential or almost tangential thrust. Slowing down or accelerating the orbital motion will cause the altitude to vary, preserving the orbital energy and angular momentum. Placing a solar sail in a 45 degree angle f…

I think it's viable. There are no other forces acting on you. Set up the solar sail at 45 degrees "against" your orbit. You will slowly but inevitably spiral into the sun without burning any fuel.

Re: Why the sun is a poor dumping ground for nuclear waste (2010)

#162

Post by lmm » Tue, Apr 14, 2015, 9:16 AM UTC

johngalt wrote: post #136

TylerE wrote: post #25

Earlier quoted context omitted.

So, getting to the sun is actually really hard, the earth is moving around the sun at ~30km/sec. For comparison, a satelite in low earth orbit is only moving about 8km sec. 30km/sec is a LOT of velocity change, and you'd need to cancel practically all of it to actually fall into the Sun. Way harder than getting to any of the planets.

Let me put it another way. If it is comparatively cheap to get to any of the other planets. Couldn't we just go to Neptune and stop our orbital velocity from there where it's only 5kms? How about exiting planetary orbits retrograde? It seems like larger planets would have escape velocities that are larger than their orbital velocity. Why couldn't our space barge leave Jupiter's orbit on a trajectory that would inters…

> Couldn't we just go to Neptune and stop our orbital velocity from there where it's only 5kms?

Yes. This is a bi-elliptic transfer, it's a standard technique, and another thread claims it would save about 40% of the required dV.

> How about exiting planetary orbits retrograde? It seems like larger planets would have escape velocities that are larger than their orbital velocity. Why couldn't our space barge leave Jupiter's orbit on a trajectory that would intersect with the sun?

It could. That's a gravity assist, and it's the only practical way to go just about anywhere with current technology (all our interplanetary probes do that).

(There are arguments against using either with nuclear waste, but I don't think the page is seriously talking about that)

If you're interested in this stuff, definitely play Kerbal Space Program.

Re: Why the sun is a poor dumping ground for nuclear waste (2010)

#163

Post by lmm » Tue, Apr 14, 2015, 9:25 AM UTC

Houshalter wrote: post #144

leni536 wrote: post #142

Earlier quoted context omitted.

That's not how it works. It would just place the waste on an elliptical orbit around the Sun.

But aren't the vast majority of possible orbits unstable? If the Earth were travelling just a bit slower wouldn't it slowly spiral into the sun?

No, just the opposite. Given any position and velocity relative to the Sun (or the Earth), an object in that position at that velocity is in an "orbit" that will be a conic section of some sort. Most of them are ellipses i.e. stable. The only way to not be in a stable orbit is to go fast enough that it becomes a parabola or hyperbola - a flyby - or slow enough that the ellipse becomes so narrow that it's just a straight line (or rather, narrow enough that it hits the thing you're orbiting).

When you throw a ball it flies in a parabola, right? But actually that parabola is just one end of a very long, narrow ellipse, with the Earth's centre as one of the foci. If you could "turn on noclip"[1] and allow the ball to fall through the Earth, it would already be in a stable orbit.

(If you want to get a better intuition for this kind of thing, play Kerbal Space Program)

[1] And if the Earth were a point mass located at its centre, which it isn't. And ignoring air resistance.

Re: Why the sun is a poor dumping ground for nuclear waste (2010)

#164

Post by hga » Tue, Apr 14, 2015, 11:48 AM UTC

dkbrk wrote: post #134

tbrownaw wrote: post #106

Every time the question of nuclear waste disposal comes up, someone is sure to say, “Why not shoot it into the Sun?” It seems so obvious. Or we could get over our stupid fear of recycling. The stuff's only hazardous because we haven't taken all the energy out of it yet. Nuclear fuel reprocessing is performed routinely in Europe, Russia and Japan. http://en.wikipedia.org/wiki/Nuclear_reprocessing

In particular, pyroprocessing ( http://www.cse.anl.gov/pdfs/pyroprocessing_brochure.pdf ), which can separate out all actinides forming the bulk of nuclear waste. The actinides can continue to be used as fuel in an appropriate reactor, leaving just small amounts of short-lived ( This was nearing completion in the form of the Integral Fast Reactor ( http://en.wikipedia.org/wiki/Integral_fast_reactor ) at the Argonne N…

Note also that civilian reactor "waste" brewed for more than a month has a mix of plutonium isotopes that makes it entirely unsuitable for practical nuclear weapons. Yeah, you can get a bit more than a squib if you're e.g. able to dissipate 100kW of heat (!) from the Pu-238 that's used for deep space probes, but the Pu-240 that made Hanford reactor plutonium unsuitable for the planned "Tall Man" gun assembly bombs strictly limits the potential yield.

This is cargo cult science at best, call it an allergy to anything "nuclear". Sort of like how the government collects a huge tax on reactor "waste", used it to build the Nevada Yucca Mountain repository (temporary construction jobs are always popular, as is "free" money), but just somehow never is going to get around to actually using the place. Well, that might change when Harry Reid retires, we'll see (heh, never considered that he was roughed up so badly he lost the use of his right eye due to eeeevil corporate nuclear power types, instead of his brother or "the mob").

Re: Why the sun is a poor dumping ground for nuclear waste (2010)

#165

Post by wongarsu » Tue, Apr 14, 2015, 12:04 PM UTC

lmm wrote: post #159

wukerplank wrote: post #139

Earlier quoted context omitted.

The problem with nuclear waste is that you need a 0% failure rate or you might detonate a dirty bomb in the atmosphere. It doesn't matter how often it worked if it fails once. Also it's a great target for sabotage for radicals.

> you might detonate a dirty bomb in the atmosphere Which would put less radioactive material up there than coal power plants already do as a matter of course.

But it's a bit hard to say at which altitude the failure would occur. Plenty of rockets have exploded on the launch pad.

Re: Why the sun is a poor dumping ground for nuclear waste (2010)

#166

Post by tbrownaw » Tue, Apr 14, 2015, 12:28 PM UTC

mahranch wrote: post #154

opo wrote: post #135

Earlier quoted context omitted.

None of the countries that have developed nuclear weapons have gotten their plutonium from nuclear waste because there are much easier ways to get weapons grade plutonium. Form the wikipedia page: "Ordinarily (in spent nuclear fuel), plutonium is reactor-grade plutonium. In addition to plutonium-239, which is highly suitable for building nuclear weapons, it contains large amounts of undesirable contaminants: plutoniu…

> None of the countries that have developed nuclear weapons have gotten their plutonium from nuclear waste Just because someone hasn't done it before doesn't mean someone won't in the future. You're also ignoring the larger threat to that plutonium; the issue that someone may not want to separate the contaminants. If they're making a dirty bomb, they don't care if it has contaminants or not.

You're also ignoring the larger threat to that plutonium; the issue that someone may not want to separate the contaminants. If they're making a dirty bomb, they don't care if it has contaminants or not.

So which is worse for that, having a fuck-ton of seriously nasty stuff sitting around forever, or concentrating the nasty stuff to a much more manageable volume and then fairly quickly shipping it off to be destroyed (in a way that just happens to provide useful energy out of the deal).

Re: Why the sun is a poor dumping ground for nuclear waste (2010)

#167

Post by hydrogen18 » Tue, Apr 14, 2015, 12:30 PM UTC

tsotha wrote: post #133

hydrogen18 wrote: post #102

Earlier quoted context omitted.

Well yes, it could be fuel in the future. But at current in the US it is stored in holding pools all over the country. None of those are getting any larger, although they are frequently reworked to allow better use of the volume available. Very little of it is 'weapons grade' and not many people have access to the equipment to weaponize it into a nuclear weapon. But turning any of it into a dirty bomb is trivial if y…

Oh, we definitely should open Yucca Mountain. Maybe with Reid out of the Senate it will happen. But we definitely don't want to "get rid" of it.

Yes, but unfortunately logic and reason don't factor into the decision making around nuclear energy policy.

People love to point scream and shout about the dangers of nuclear energy. In conversation I've noticed that people think of nuclear energy as interchangeable with nuclear weapons. Nuclear weapons are incredibly difficult to build compared to a nuclear fission reactor. The experimental data you need to build one either requires numerous tests or stealing it from a government. Nuclear reactors on the other hand, can be very simple. The simplest reactors are just lumps of radioactive material carefully bonded to thermoelectric devices! The biggest risk from a conventional nuclear reactor is a steam explosion and the dispersal of radioactive material. I reckon the second biggest risk is having tons (quite literally) of spent fuel laying around the country for no good reason. The storage ponds aren't 100%, accidents will happen. For most of the ponds if the cooling systems went offline the water would boil away and then the fuel would self-heat till it started to oxidize. At that point you've basically got hundreds of miniature fallout generators going. You better hope the structure above the pond is airtight because no one is going to be entering it again in this century.

The same group of people that scream and shout about nuclear energy being unsafe seem to actively ignore the dangers of conventional energy generation. For example, steam explosions are still a risk to the employees operating the plant. But I guess their lives don't matter? The pollution from coal isn't exactly helping the environment. Then there is this matter of what to do with all of the coal dust after it is burnt. You know, the same coal ash that over 1 billion gallons recently flooded an area of Tennessee. This contaminated a river, people's land, and destroyed their homes.

Even if we ceased 100% of nuclear energy generation today, we still need Yucca Mountain to deal with the spent fuel we already have. It seems that some groups in the US believe that if they scream loudly enough, the problems of the world will simply go away.

Also there is this issue of the fact that the energy consumers and the taxpayers already paid for the fucking thing but aren't getting any of the benefits. At this point it is basically just a boondoggle.

Re: Why the sun is a poor dumping ground for nuclear waste (2010)

#168

Post by dalke » Tue, Apr 14, 2015, 12:40 PM UTC

lmm wrote: post #161

exDM69 wrote: post #151

Earlier quoted context omitted.

Your calculations seem sensible, but you're only talking about radial forces, ie. countering the "downward" force of gravity with "upward" thrust of a solar sail. But space flight maneuvers typically use tangential or almost tangential thrust. Slowing down or accelerating the orbital motion will cause the altitude to vary, preserving the orbital energy and angular momentum. Placing a solar sail in a 45 degree angle f…

I think it's viable. There are no other forces acting on you. Set up the solar sail at 45 degrees "against" your orbit. You will slowly but inevitably spiral into the sun without burning any fuel.

If you have effective solar sail technology then all my calculations are thrown out the window.

If you don't, then the time to spiral into the sun is large. Figuring 5/64 N on 20 tons and an orbital velocity of 30km/s gives

  t = v / a = 30 km/s / ((5/64) N / 20000 kg)
    = 245 years to cut the orbital velocity

This assumes all of the force could be used to slow the waste hauler. As http://en.wikipedia.org/wiki/Solar_sail points out, the force is cos^2(theta) so the actual time at 45 degrees is

  t = 245 * (sqrt(2)/2)^2 = 490 years.

The actual time will be smaller because you only need to hit the sun, and solar wind will get stronger. So, 350 years? As a wild-ass guess.

That same page points out that sails don't work much inside of 0.25 AU, because the temperature can exceed the material properties of the sail. Though I think if the apogee is inside of 0.20 AU it's good enough.

To make it worse, the solar wind fluctuates, so unless there's active control on the rocket, its orbit will be unpredictable over the centuries. When it's still near Earth orbit, or when it approaches Venus orbit, what are the chances of a gravitational assist leading to an Earth-return?

With 50,000 tons of high-level waste, and 15 tons per rocket => 3,333 rockets in uncertain orbits, the chances become much higher.

Re: Why the sun is a poor dumping ground for nuclear waste (2010)

#169

Post by WayneS » Tue, Apr 14, 2015, 1:27 PM UTC

Ok, continuing the argument from the article and not discussing practical methods of waste disposal...

Instead of using chemical rockets for the entire dV how about using a rocket to get into orbit and then using an ion engine driven by solar energy to lose the additional 20km/s? It seems the "fuel" weight required would be significantly less.

Re: Why the sun is a poor dumping ground for nuclear waste (2010)

#170

Post by regularfry » Tue, Apr 14, 2015, 1:53 PM UTC

mahranch wrote: post #154

opo wrote: post #135

Earlier quoted context omitted.

None of the countries that have developed nuclear weapons have gotten their plutonium from nuclear waste because there are much easier ways to get weapons grade plutonium. Form the wikipedia page: "Ordinarily (in spent nuclear fuel), plutonium is reactor-grade plutonium. In addition to plutonium-239, which is highly suitable for building nuclear weapons, it contains large amounts of undesirable contaminants: plutoniu…

> None of the countries that have developed nuclear weapons have gotten their plutonium from nuclear waste Just because someone hasn't done it before doesn't mean someone won't in the future. You're also ignoring the larger threat to that plutonium; the issue that someone may not want to separate the contaminants. If they're making a dirty bomb, they don't care if it has contaminants or not.

Plutonium makes a rubbish dirty bomb, it's too heavy to disperse.