Crazy Idea for Nuclear Waste Disposal

[Connor11]

Hi I’m a high school senior taking physics and had this crazy idea for nuclear waste disposal.

Given:

• Space is a good place to put nuclear waste
• Rockets can malfunction possibly leading to their nuclear waste payload being being dispersed

I thought of looking toward a rail gun. I found a preliminary assessment by nasa
https://ia700501.us.archive.org/14/items/nasa_techdoc_19820021469/19820021469.pdf

but I saw a major flaw: If the gun malfunctioned nuclear waste could still be launched but fall back to Earth at an unknown location.

My addition to their plan would be to have baffles like at a gun range but in reverse. (see figure) This baffles are circular in shape but with a opening for the nuclear waste projectile. The openings are positioned to stop a projectile not within tolerances with regards to angle and speed. With the known target velocity (~ 20 km/s), angle, and acceleration due to gravity the path that the projectile would take would be calculated and any projectile not on this path would be stopped.

The key benefit to this idea is that if something were to happen during launch the nuclear waste would collide and at least be in a known location instead of somewhere in the sea. There would not have to be a search effort and the possibility of losing the projectile.

So because my knowledge is exhausted I turn to you guys to assess the feasibility of this solution from a physics perspective and the risks involved.

Also...

• Will air resistance make it impractical?
• Will air resistance melt the projectile?
• How can the baffles and projectile be design so that a collision would minimize the dispersion of nuclear material?

• How much certainty at launch is there that an aircraft/satellite/space debris is not in the way?

Thanks,
Connor

 

[Bandersnatch]

Hi Connor11, welcome to PF.

• Will air resistance make it impractical?
• Will air resistance melt the projectile?

The assessment calls for a projectile design able to withstand atmospheric heating as well as reentry in case of an accident. Consider, at worst you end up with a leaking container somewhere in the ocean. Which is not optimal, but compare with having the 2 tonne projectile hit a solid obstacle at 20km/s. That's $~4*10^{11} J$ of kinetic energy to dissipate. No matter what you make the baffles from, the projectile will vaporise on impact. You then end up with the launcher site, and potentially large extended area, contaminated with the payload.

Additionally, and perhaps more importantly, try and calculate how far from the barrel exit the baffles would have to be to catch (say, deviation of 1m from the target path) a projectile going at 1/2, 1/4 or 1/10th the target muzzle velocity. Remember that the assessment calls for 20 degree elevation of the gun barrel.
Use the projectile motion equations.

 

[Blackberg]

The question that comes to mind is what is the most energy ever imparted to a projectile by a rail gun, and how much more would be needed to break away from orbit.

 

[mfb]

For an emergency abort system, it would be easier to block the exit in some way. That still vaporizes the projectile, but you have some chance to catch most of its debris in some way at the end of the pipe.

How much certainty at launch is there that an aircraft/satellite/space debris is not in the way?

For a single pass, this is not an issue. And you would launch a massive block, not fragile solar cells, so impacts from small objects would not matter much. The ~20000 tracked objects larger than a few centimeters are distributed over ~5*10^14 m^2 (seen as projection on the surface), the chance to hit one of them (get closer than ~1m) is negligible.

Air resistance is an issue, for sure. You would probably build this on a mountain, or even use some floating structure to get a vacuum up to higher altitudes.

 

[Connor11]

4∗1011J~4*10^{11} J of kinetic energy to dissipate.

it would be easier to block the exit in some way

as a revised idea the projectile could just be smaller (10kg) and fired a lot more times. the gun could be positioned near a mountain that has a heavy block (2*10^7 kg suspended by explosives. If a deviation occurred as detected by sensors the block would fall and absorb the impact. (by obtaining a velocity of 1 m/s)
KE = W = mv
.5 *10* (2000)^2 = 2*10^7kg * 1m/s
density of concrete = 2400kg/1m^3
therefore block would be around ~20m cube

does that seem reasonable?

 

[Bandersnatch]

You can't make the projectile that small. The bulk (90%) of the two tonnes of the projectile in the assessment document is the atmospheric (and radiation) shielding. A 10kg projectile at 20km/s will vaporise before leaving the atmosphere. The document details the reasoning behind making the projectiles that large, and why minimising the number of launches is desirable.

Have you tried calculating how far away (and how tall) the mountain would need to be from the launcher for the design to make sense?

 

[mfb]

Kinetic energy is not conserved in such a collision. Momentum is conserved. This would lead to a smaller velocity - but it still means the projectile is hitting a solid wall and gets vaporized (note that 2km/s is not sufficient to leave earth).

 

[anorlunda]

Perhaps the craziest part of the idea is to dispose of it in the first place. At least one country, Sweden, required that their nuclear waste be stored retrievably. They figure that in a century or two it might be immensely valuable for medical isotopes.

The danger of nuclear waste storage has been vastly overstated. School children should be taught that. That is an opinion, not science.

Science could provide estimates of the risk in nuclear waste deaths per year for the whole globe to compare with deaths per year from war, or diseases, or obesity, or car accidents, but I have never seen such direct comparisons. Perhaps another PF reader could supply a link.

 

[Bongo]

Yes not to mention further technological advancements that would allow other uses for these rare heavy elements.

 

[BillyT]

Send it down, not up:
After 10 or so years in "swimming pool" storage, as now, "glassify" the waste in disks about two feet in diameter and inch or two thick. (A surface to volume ratio high enough so self heating does not soften glass, or quartz if need be. Disk can have thin pure glass outer layer to stop non-gamma radiation. Water cooling could continue if needed during transport)

Then with automatic handling (avoiding gamma rays injury to people) load onto special boat with Aegis ships as escort for trip to deep ocean trench. The subduction zone just North of Puerto Rico is more than 8 miles deep. Automatic "hurler" like large version of the "clay pigeon" hurler used for shot gun practices, slings disk over the ship's stern to start their 100 or so million year trip deeper into the earth. Their shape will assure they rest initially in the bottom mud well separated from each other in a swath several miles wide even with launch rate of 1 per second.