Liquid fluoride thorium reactor

[floss]

I was wondering what are the implications of a Liquid fluoride thorium reactor   to future spaceflight  are they useable in a engine or only as a traditional nuclear plant ?

[QuantumG]

Every design I've seen intended for flight has terrible power/weight. i.e., to the point that they don't even make sense for powering an aircraft.

[floss]

Thanks would you have any pointers as where to see some of those designs ?

[QuantumG]

Here's a brief history, with some pictures.

http://energyfromthorium.com/2006/04/22/a-brief-history-of-the-liquid-fluoride-reactor/

I expect it was on NTRS that I found various other documents, but it might have been, ya know, the library.

Been a long time since I looked at it.

[floss]

Thanks with recent developments in thorium I was thinking of a dual mode reactor with 2 radiators one in the h2 fuel thank to skyrocket the pressure  and the other to provide power.

[sdsds]

Nuclear reactors of some type (and LFTRs are definitely front-runners) are going to be super-important for electricity-intensive, long-duration missions,  operating where solar power is insufficient. One kind of electricity-intensive mission is the kind that uses some form of electric propulsion, like ion engines. But if the LFTR has a useful life of 30 years ... what type of mission needs ion propulsion for that long? Shuttling main-belt asteroids closer to the Earth?

[john smith 19]

I was wondering what are the implications of a Liquid fluoride thorium reactor   to future spaceflight  are they useable in a engine or only as a traditional nuclear plant ?

Minimal as an NTR. Possibly a bit better for on site power if you're talking settlement.

[IanO]

Thanks with recent developments in thorium I was thinking of a dual mode reactor with 2 radiators one in the h2 fuel thank to skyrocket the pressure  and the other to provide power.

What recent developments? The only news on thorium in the last five years has been futile attempts to raise interest and funding in the west. As far as I can tell no actual research or development programs have been initiated except in India and China.  India has large thorium reserves, but is more interested in mixed-oxide solid fuels for their existing CANDU technology.  Only China is going after LFTR with any real support, because they are frantically pursuing all non-polluting energy sources.

Nuclear reactors are massive, and the LFTR concept only had a lunar application because it didn't require high pressure water cooling. I don't think even LFTR has the power-to-weight ratios that make it attractive for spaceflight applications, and the many moving parts are not good for long-term reliability compared to solar and nuclear-thermal.

Hopefully, Kirk Sorenson himself will chime in on this; I think he still monitors this site.

[butters]

As I understand it, the principal operating advantages of the LFTR are efficient consumption of long-lived isotopes and the primary fluid loop runs at atmospheric pressure. These advantages are very relevant to terrestrial reactors, but not so much for off-world applications. That molten salt may plug a leak on contact with the Earth's atmosphere, but it will behave differently in deep space.

[ArbitraryConstant]

I was wondering what are the implications of a Liquid fluoride thorium reactor   to future spaceflight  are they useable in a engine or only as a traditional nuclear plant ?

The alleged advantages, even if they can be demonstrated, aren't really helpful ones for spaceflight. The disadvantages like having to manage the fluid would be worse.

Like naval reactors, space reactors will likely prefer HEU.

[Vultur]

Nuclear reactors of some type (and LFTRs are definitely front-runners) are going to be super-important for electricity-intensive, long-duration missions,  operating where solar power is insufficient.

Yeah. Though as lighter solar panels are proven in space that area may shift outwards significantly. I think IKAROS had 25 um thick solar panels... if they only have to stand up to the tiny acceleration of electric propulsion and so don't need much of a support structure, you could get quite a bit of power per mass even out at Jupiter, maybe even Saturn.

(I don't know the density of IKAROS' solar panels but silicon is about 2 g/cm^3, so by that assumption about 20,000 square meters would mass 1 tonne. At 5 AU sunlight should be about 4% of at 1 AU or something like 54 W/m^2 ... if the panel is 12% efficient that's about 6.5 W/m^2 or 130 kW for that 20,000 square meters. 10 AU near Saturn would be about a fourth of that....)

I'm sure it would be more complicated than that in real life, power cables would have mass and even supported on a solar sail like IKAROS the support structure would have some mass, but still....

[Adaptation]

Every design I've seen intended for flight has terrible power/weight. i.e., to the point that they don't even make sense for powering an aircraft.

Same could be said about the solar panels we use in space flight.  OK yes some ultra light weight drones use solar but comparing aircraft use to space use doesn't make much sense to me.

[cordwainer]

Fuel cells and metal-air batteries, you already have to carry chemical fuels and ionizates for propellant so it makes more sense to get some energy directly from the propellant for use on a spaceship.(unless you have some very energy intensive onboard task) For terrestrial applications in space solar, nuclear and fuel cells all have certain advantages. For propulsion though unless your building an NTR there is not as much need to carry an onboard nuclear reactor, even in the case of a large scale electric propulsion system beta-emitting thermocouples and RTG's can provide sufficient power for most applications with a smaller weight and safety penalty.

[Adaptation]

Yes but soon the only one with any plutonium-238 will be Iran.   

[hellofu]

LFTR would be better than any other active nuclear fission reactor then maybe a traveling wave reactor. the real advantages are in it safety, ease of fueling and power/ temperature control. the basic principles that make a LFTR great apply to space except the gravity based safety system.

[vulture4]

For space I think the conventional HEU reactor is simple, power dense, and remains a good choice, at least until the fluoride salt system has a lot of ground service experience. Coupled with the 50Kw hall effect thrusters planned for the asteroid retrieval mission an HEU reactor would greatly reduce transit time for planetary missions beyond Mars.

[john smith 19]

So what exactly  do people plan to use this reactor for?

Keep in mind some of it's key benefits, like purging off Xe135 (a major reactor poison) doesn't work so well without a gravity field.

It's standard operating temp is tiny next to an NTR, as is it's P/W ratio.

BTW if you're looking to run a sustainable self expanding colony you'll need to be able to do it with natural Uranium or Thorium, because enrichment is a major PITA, needing very specialized ITAR controlled stuff in large amounts. 

[ArbitraryConstant]

LFTR would be better than any other active nuclear fission reactor then maybe a traveling wave reactor. the real advantages are in it safety, ease of fueling and power/ temperature control. the basic principles that make a LFTR great apply to space except the gravity based safety system.

Not really, and doubly incorrect for traveling wave.

I think there's a lot of misconceptions going around about exactly what makes different reactor designs good or desirable for one thing versus another, and I think the people advancing thorium or various fast breeder concepts for spaceflight are straight up missing that information and coming to conclusions that don't make sense. Watching a youtube video on LFTR just isn't going to give you that information.

What about current reactors does LFTR seek to improve on? It wants reduced waste volume and half life. It wants improved safety. It wants lower cost. It wants higher temperatures. It claims to want more fuel availability, but that's a non-issue and therefore a red herring.

Why can't light water reactors deliver this? Well, the relatively low enrichment of the fuel means they're mostly U-238, so you have the nasty stuff mixed in with a huge volume of a benign material. Additionally, U-238 gets bred into higher actinides which have long half lives, so it makes the waste problem much worse, and this adds to the heat load in shutdown, which is a safety flaw (see Fukushima). Being water cooled also limits temperature.

Ok, so why is LFTR bad for spaceflight? As John points out the technology needs gravity for a number of reasons. You have to do stuff to the fluid, when solid fuel elements would be better.

So can we get those advantages with solid fuel? As it turns out we can. HEU doesn't have the U-238 to deal with. This means it doesn't have all those actinides to deal with. Proliferation concerns prevent us from using this in civilian reactors on Earth, but not really for specialized space stuff any more than naval reactors. Typical naval reactors use water as moderator and coolant, but there's no reason a space reactor couldn't be graphite moderated and use molten metal or gas as coolant, with commensurately higher temperatures.

It seems to me LFTR wants to solve problems space reactors don't have, and it'll cause problems HEU reactors don't have.

[Adaptation]

AFIK thorium is supposed to have a very good fuel to energy conversion ratio and very low quantity of dangerous byproducts.  Thorium reactors could be a good powersource for a generational starship or an alternate to solar for an Aldrin Cycler. 

[mmeijeri]

Isn't a LFTR a more likely choice for a surface reactor?