Systems and Cost Analysis for Nuclear Subterrene Tunneling Machine (1973) [pdf] | Hacker News Reader

Systems and Cost Analysis for Nuclear Subterrene Tunneling Machine (1973) [pdf]

osti.gov

28 pointsbenbreen18 comments

Main problem is the rock melting temperature ~ 1500 to 2000 °C. Even the best performing nuclear fuels can only reach 1600°C in the fuel (TRISO Particle or FCM fuel) for limited periods of time, meaning 1000°C of heat delivered due to major limitations in the steels and heat transfer. They realized this early on in the Subterrene project at Los Alamos, and transitioned to electrically heated electrodes like graphite and tungsten. They even did field tests near Bandelier National Monument, digging a large diameter door sized hole using 100s of small diameter holes to form the perimeter. Even then, there are material degradation problems especially in the presence of air and water, that make rock melting pretty challenging. More recently, an MIT spinoff (Quaize or Quarkz or something like that) is using microwave emitters to vaporize the rock - which reduces material and mechanical challenges. But it's not ideal for large diameter holes - mostly for geothermal, fossil, or utility boring.

It's not clear to me that melting is less energy intensive than digging (and all it's related machinery and material movement).

I think this problem may be one if the classic solid state is not actually better than the old-school mechanical solution.

As an experiment, it would be fun to architect 2 designs. One that has a fancy microwave or thermal rock melting setup, one that has a traditional rock drilling approach, both powered by a nuclear power source. Add up the cost of ownership for both, and I'd bet the mechanical solution comes out on top.

Fully agree

With current technology. But the point of this is to get a starting point for solid state and improve afterwards. Very much like how jet engines came to be better than propellers.

I think it's pretty clear from an energy perspective that melting/vaporizing or even pulverizing the rock is waaaaay more energy intensive as the force to shear rock is orders of magnitude less than melting it.

One way to think of this is to just imagine the chemical bonds holding the rock together. Tricone drills and TBMs both just sheer the rock, the latter on a massive scale, which is only has to expend that localized bond energy, whereas melting all of it is massively inefficient even with good heat recovery.

One thing I've wondered is if a focused energy beam could just locally break the bonds in a way that'd produce pieces optimized (size, shape, etc.) for transport back through the tunnel. In this way the minimum of energy needs to be expended by reducing the linear distance of cutting.

However, energy beams still have to heat up the rock a lot to vaporize it, so this would still locally be less efficient than cold sheering that current methods use, so when you think about it, TBMs, etc. are actually doing pretty good.

Could you use a nuclear element to directly create pressure waves against the material? Something like: nuclear fuel, graphene drum head, water injectors to drive the drum expansion.

Why does efficiency matter at all? Tunneling costs thousands of times more than the energy cost.

A far more 'sensible' approach to rapid tunnel construction was experimentally tested in the 70s. The Rapid Excavation And Mining(REAM) project showed how high speed kinetic projectiles could be used to to rapidly fracture rock to dig a tunnel.

This is a fancy way of saying that someone dug a tunnel through rock by repeatedly shooting at it with a tank.[0] This was found to be impractical due to the cost of gun powder.

However, a company has proposed a supersonic ramjet accelerator instead of a conventional gun to accomplish this. SCRAM accelerators use a specially shaped projectile that acts as a SCRAM jet when it's inside a tube full of fuel/oxidizer, which may be much cheaper than gun powder.[1] They have started to demonstrate fracturing rock walls with this approach.

[0]https://apps.dtic.mil/sti/pdfs/AD0757116.pdf

[1]https://www.hypersciences.com/applications/

Using an electromagnetically accelerated projectile, such as one from a rail or coil gun, could reduce the cost even further, since no fuel would be required. Has that been considered?

Imagine if all the national labs just designed tools like this to be built for the betterment of humanity instead of weapons. Humans are so silly.

Skeptoid recently covered this topic in the context of the conspiracy theory that the soviets were weaponizing such technology: https://skeptoid.com/episodes/4845

The soviets did something of almost the same level of sanity, they used rockets to dig holes rapidly.[0]

An underground rocket is basically a specialized rocket nozzle pointed straight at the ground, the hot fast moving exhaust gases are able to excavate soil and rock. Speed up to 100 m/s through soil and 5 m/s through solid rock have been claimed. Here's a video of a missile being repurposed to do this[1].

I've read, although I forget where, that there were concerns the soviets could use this technique to quickly place a nuclear weapon under west germany as part of a nuclear first strike. I suspect these concerns were quite short lived

[0]https://en.wikipedia.org/wiki/Underground_rocket [1]https://www.youtube.com/watch?v=e7_tRmSIIEo

Same engineers that designed the firefighting tank with two MiG engines?

https://www.caranddriver.com/features/a15138374/stilling-the...

> 100 m/s through soil and 5 m/s through solid rock

The Wikipedia article says meter/minute where it mentions those numbers, not meter/second.

Looks like they stuck a conical diverter onto the exhaust end of a solid-fuel Grad artillery rocket.

Pretty cool.

There are a lot of issues today and coming in the near future, that thinking big and outside the box isn't just useful but potentially even a necessity!

This sounds like an ideal candidate for nuclear. It’s underground functioning would make it relatively safe? And it wouldn’t cost a lot of fuel.

It would be fun if it ran a random walk guidance system of a roomba, and you could just let it go on its own. When will it visit your city? Oops, a high pressure magma pool, better turn around.

Like a cursed Thomas the tank engine.

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