Specs on current nuclear reactor technology

[PTNLemay]

After having watched this:

I've been wondering...

What is the current status of compact military nuclear reactors? I'm curious primarily because those are exactly the kind of reactors we could use in a large interplanetary spacecraft. Something that could power one of those big VASIMR engines that some people claimed could get people to Mars in 40 days. The problem is these are always so classified, and finding detailed specs is difficult.

All I really know is a few bits and pieces of last generation. The Ford is going to use the new A1B reactor (totally classified) but we know the Nimitz used 2x A4W, giving it a total of 208 MW in it's engines. We can assume the new reactor will be somewhat better than this at least.

That brings up another question though, how efficient are the engines. Ground-based reactors are around 33% efficient, so you'd need 100 MW of heat from the thing to produce 33 MW of actual electrical power. And I know most 20th century submarines were even less efficient than that because the reactors were so small (they operate around 25% efficient). Are super modern reactors somehow more efficient than that? Another thing I wonder, how heavy are these reactors exactly? It's all fine and dandy if you can produce 200 MW needed for the VASIMR, but not if the reactor itself is 100 tons.

I don't mean to unveil any state secrets or anything... I'm just really curious for the sake of realistic sci-fi (in an up-to-date sense).

http://en.wikipedia.org/wiki/Gerald_R._Ford-class_aircraft_carrier

http://en.wikipedia.org/wiki/A1B_reactor

http://en.wikipedia.org/wiki/A4W_reactor

[Warhorse]

Naval reactors aren't really suitable for spaceflight, as they all weigh at least hundreds of tons. The last I heard, the biggest reactor anyone had flown was rated for a couple of hundred KILOwatts, on late Cold War era Soviet radar ocean recon satellites. The infamous Kosmos 954 was such a beast.

[PTNLemay]

It would still be nice to know stuff like thermal power output and electrical power output on these modern ones.

[bradley101]

I know of the SAFE-400. Developed at Los Alamos National Laboratory and Marshal Space Flight Center. Uses Uranium Nitrate as a fuel. 10x the power the weight ratio to the SP-100 project in the 1980s. Only weighs 512 kilos. Max core temp 1020 degress Celsius.

100KW Electricity energy

400KW Thermal energy

Source

http://www.world-nuclear.org/info/Non-Power-Nuclear-Applications/Transport/Nuclear-Reactors-for-Space/

http://en.wikipedia.org/wiki/Safe_Affordable_Fission_Engine

Hope this helps.

[bradley101]

Just to mention about the VASIMR 40 days yes but the T/W is so low just like any ion or plasma engine. The low T/W ratio means you spend a year or so gaining velocity that means for manned missions you are exposing your crew to high radiation out of the van Allen belts. Excellent for cargo but for crewed missions I would rather trade off specific impulse for a T/W ratio greater than 1 for a 9 month Hoffman transfer than 13 month transfer including the long slow acceleration.

[Scotius]

100 kW output? That's a bit of a letdown Prototype 200 kW VASIMR would gobble it up in no time. I guess advanced engine is only half of the answer. Hmmm...maybe we should invest into Fusion Pulse Drive instead

[Idobox]

The other big difference between naval and space nuclear reactor is cooling. Ships are conveniently close to large amounts of cold water, so the heat sink is simple. In space, dumping heat is difficult, which means a higher temperature of the cold point, and lower efficiency.