How small can you make a nuclear reactor? Could you make one

>>8173005
Forty millimeters.
Yes.

>>8173008
That sounds like it might be a nuclear battery, not a reactor...

>>8173012
Since you seem to have a size in mind and 40mm is as small as we can get. Go up from that until you hit your smallest size possible that you still consider a reactor.

>>8173033
Sorites paradox, much?

>>8173041
>Sorites paradox
How? We know that at SOME size a reactor can exist. You seem to be attempting to sound profound.

>>8173056
Yes, but a which point isn't it, as anon defined it: "a nuclear battery"? - Also, I happened to have been joking, so be less solemn.

>>8173033
There's a minimum size for a sustaining critical reaction, and there's a minimum size for the required shielding for safety.

Not sure.

For reference, see:
https://en.wikipedia.org/wiki/American_submarine_NR-1

>>8173033
how small can you make nuclear reactor that produces power through a turbine with steam/etc

>>8174907
That really depends on your boiler/turbine technology. You could probably build a boiler and turbine that produces some power from even the smallest reactor, however the OP asks about fitting one to a locomotive, which implies a certain final power output - say 5 MW at the shaft if we want performance comparable to a conventional steam 1930s/1940s era passenger express locomotive.

Turbine generators in modern nuclear power stations have an efficiency slightly better than 33% in converting thermal energy into electricity. If the nuclear locomotive uses mechanical drive, you wouldn't need to worry about any efficiency loss in the generator specifically, but the turbine efficiency would likely be worse due to miniaturization. 20% would seem a reasonable estimate to be safe. Which means we'd need a reactor producing 25 megawatts thermal.

Unfortunately, I don't know of any reactors in that range so I really can't estimate what the power/volume requirements would be. Although, you wouldn't need it to fit in the space of the firebox, as you could simply replace the tender with a reactor car feeding steam to the locomotive.

>>8175025
*can't estimate what the WEIGHT/volume requirements would be

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you could probably fit this on a train.
https://en.wikipedia.org/wiki/Nuclear-powered_aircraft

>>8175082
I think the aircraft reactors were around 2.5 MWt. You'd need something like ten times that for a locomotive.

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>>8173005

yes you can. Or at least theoretically so.

http://io9.gizmodo.com/the-days-of-atomic-locomotives-in-america-1564623650

It was never developed because the heyday of nuclear power happened when the American railroad industry was falling apart due to 1930s era price controls (on shipping rates) and the Interstate freeway network. By the time the industry began recovering in the 1980s and 90s, exotic experiments in new propulsion tech were over. American railroads themselves aren't even interested in electrification, either. Mostly because they've now whittled down their locomotives to about fourish families from GE and EMD.

The #1 problem isn't the technology, or the onerous EPA licensing process (which the RRs are fully capable of lobbying to their benefit). It's the staff requirements. A bona fide nuclear reactor would require a licensed technician running it in effect more than tripling their per train staff cost. This is a problem given that both west coast railroads (ie ones that most benefit from fuckhuge locomotives) run over 100 trains each day through LA alone.

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>>8175702

On another note, the RRs themselves turned away from fuckhuge locomotives in the 1990s, thanks to the rise of computerized control systems. Before the 1980s, if you wanted to have distributed power in a train (ie one locomotive at each end) there needed to be an operator in both, controlling each throttle and communicating by radio. This is costly if you're running 7+ locos per train, as is often the case in places like Cajon Pass or Donner Pass.

Anyway, this led to the development of huge locomotives, culminating with the GE U50 and EMD DDA40X. This monster of a locomotive is the largest production diesel locomotive ever built. It was retired because:

1. maintenance costs are higher compared to having multiple "normal" sized locomotives, as the latter can use the same parts
2. maintenance costs for track are higher, because heavy locomotives do more damage
3. (as mentioned) computerized distributed power control systems eliminated the need to have one locomotive in the first place
4. even in the situation where a nuclear power source is wanted, the (aforementioned) staffing costs make one plant + catenary cheaper than 200+ mobile plants

>>8175702
>>8175716

And, finally there's this: the ACE (American Coal Enterprises) 3000. An attempt to bring back coal-fired steam trains amidst the '73 oil crisis.

http://locomotive.wikia.com/wiki/ACE_3000_Protoype_Steam_Locomotive

http://www.american-rails.com/ace-3000.html

and gas turbines in the 50s:

https://en.wikipedia.org/wiki/Union_Pacific_GTELs

In particular, diesel-electric trains today don't require a lot of specialized parts. Gas turbine, nuclear, coal etc all do (such as: drivers for wheels, boilers or turbines). Meanwhile, pure electric trains have the fewest moving parts, but the most efficiency. This is what ultimately made all of them non-starters.

>>8175702
>>8175716
>>8175727

tl;dr combination of staff costs + maintenance costs