Nuclear Turbojet Engines

[Wubslin]

Hey all!

I just had a thought. The gas Brayton cycle we all know and love from such hits as jet engines, gas turbines, and that weird car that Jay Leno owns is a perfectly respected thermodynamic cycle. It's like the steam Rankine cycle without the cool phase change benefit but with none of the sogginess you normally get between the turbine and the heat source. Well, I was thinking about how jet engines don't have to have chemical combustors after their compressors, they just need something that cranks out heat. What else cranks out heat besides a flame?

 

So yeah, it turns out there's been a lot of thought at one point into making nuclear jet engines. In fact, if you look up the HTRE devices you'll see they've been successfully run and even flown on real planes before! Just not at the same time though.

How convenient would it be to have something that can breathe Eve's atmosphere but with more propulsive heft than just a simple electric propellor? And what better way to do it than with something like the above, a barely-shielded nuclear reactor with a turboshaft running right through the core and a chemical afterburner in the back for when there is oxygen in the atmosphere? I think it could make for a pretty cool part.

Here's some food for thought:

 

 

And the full report to anyone who cares: https://www.osti.gov/biblio/12555356-xnj140e-nuclear-turbojet-section-reactor

 

 

 

[Hyperspace Industries]

So, it’s like the Torch engine from atomic age?

Awesome!  That’d be brilliant, especially since I really hope for more unbreathable atmospheres, I don’t really want to go 4 lightyears to visit Kerbin again.

[Wubslin]

25 minutes ago, Hyperspace Industries said:

So, it’s like the Torch engine from atomic age?

Awesome!  That’d be brilliant, especially since I really hope for more unbreathable atmospheres, I don’t really want to go 4 lightyears to visit Kerbin again.

Yeah. A lot of what I included in the images there is the XNJ140E nuclear turbojet, which was a General Electric project which made it basically all the way to the operational flight testing phase until Kennedy suddenly said "nuclear flight is de-cades away!" in his classic Boston accent before cancelling the nuclear aircraft propulsion program in 1961. Development for the engine soon ended, and to date a plane has never flown under nuclear power. 

The engine was expected to have an operational life of 1000 hours. The big fat thing I also posted, the HTRE-3 assembly, was successfully run at full power for almost 130 hours straight. There were a number of different designs that either had a turboshaft go straight through the reactor pile or else had multiple separate engine assemblies lead to a single reactor. It seems there never was a purpose-built compressor and turbine assembly and that the hardware used was repurposed from normal combustion turbojets.

The website link there is the blog I got most of this information from, by the way. The Convair NX2 was a bomber with an interesting split tail design meant to accommodate three of those engines.

Here's another good one: https://www.osti.gov/biblio/1048124

Hey look! A nuclear ramjet! No moving parts!

 

Edit: oh and here's a last one, another Russian design that smartly avoids sending a turboshaft directly through the reactor pile (neutron embrittlement anyone?) but does it by sending the intake air and exhaust off to the side all funky-like.

 

Edited December 14, 2021 by Wubslin

[Incarnation of Chaos]

Didn't these spew the highly radioactive fragments of the core alongside their exhaust, require a reactor pile closer to submarine levels of enrichment (20-40% U235) and a massive lead bulkhead to separate the crew from the active reactor?

Don't get me wrong, I've always loved the idea of nuclear thermal turbojets/fans/ramjets. And Kerbals don't know fear nor radiation, but I've never seen any really good proposals for alternative designs. 

[AtomicTech]

PorkJet moment

[Wubslin]

On 12/16/2021 at 6:43 PM, Incarnation of Chaos said:

Didn't these spew the highly radioactive fragments of the core alongside their exhaust, require a reactor pile closer to submarine levels of enrichment (20-40% U235) and a massive lead bulkhead to separate the crew from the active reactor?

Don't get me wrong, I've always loved the idea of nuclear thermal turbojets/fans/ramjets. And Kerbals don't know fear nor radiation, but I've never seen any really good proposals for alternative designs. 

They actually do not. That concern was speculation brought up while the details of nuclear aircraft propulsion were still being figured out and the theories surrounding their operation was in their infancy. It's still persisted, but if it matters at all just remember that a nuclear thermal rocket is essentially the same exact principle and those have been fired for long duration (just like nuclear jet engines have) without ill effect.

It is of course true that they require high enrichment, but that much is true for any reactor designed to be compact or move around. If you had the ability to travel anywhere at will, by far the easiest way to come across multiple fission weapons' worth of high enrichment Uranium would be by going to the Moon or Mars in the near decades and stealing a Kilopower reactor. Remoteness replaces security up there. Of course planes are easier to steal but this is space frog video game. For your last point, it is true that shielding weighs a massive amount but it's offset by the fact that the plane needs to carry no heavy fuel otherwise.

(Firing footage around 9 minutes or so)

 

Edited December 19, 2021 by Wubslin