Why we need a Small Rugged Reactor…
This is why:
Militants in Pakistan attacked a fuel supply convoy yesterday, killing at least four, that was bound for US military facilities inside Afghanistan. Twelve tankers were set ablaze and crews struggled throughout the night to put out the fire.
What does this have to do with thorium or LFTR?
A small rugged LFTR could provide electrical energy to these bases in Afghanistan that currently rely on shipments of vulnerable petroleum. Furthermore, the high-temperature capabilities of LFTR mean that we could also synthesize hydrocarbons to fuel vehicles on site, rather than trucking them in.
How would it work?
A small LFTR unit would be brought in to a military site in the form of a few standard containers. One would hold the reactor, its fuel and blanket processing system, and the primary heat exchangers, all within a strong and sealed containment system. The fact that LFTR operates at low pressure would mean that this containment would be close-fitting to the reactor. This is very different than the containments required on today’s water-cooled reactors, where they have to accommodate the expansion of high-pressure water into steam that can happen if pressure is lost. In a LFTR, the system is at low pressure and there is no high-pressure water or other gases inside the containment. The only thing that goes in is coolant salt and the only thing that comes out is coolant salt.
This whole assembly would be lowered into a below-ground concrete bunker. The gas turbine power conversion system would be brought in and attached to the coolant salt system. Coolant salt would heat gas that would drive turbines and generate power. The gas used in the power conversion system would be air-cooled via large air intakes and outlets.
How could we generate hydrocarbons? Using the electricity from the LFTR, we crack water electrolytically to generate hydrogen and oxygen. The hydrogen is reacted with carbon (either brought in to the site or extracted from CO2 in the air) to form synthetic hydrocarbons to power vehicles and aircraft.
The fuel for the LFTR would be brought in separately from the reactor, and when it was time to leave it would be removed from the reactor first. The reactor would not be transported with fuel or blanket material onboard.
Why consider LFTR versus other designs?
LFTRs can operate at low pressures. Pressurized-water reactors can’t and gas-cooled designs like the pebble-bed reactor can’t. Low-pressure operation means you can have a compact unit with a close-fitting containment and no risk of high-pressure explosions.
Liquid-metal-cooled designs like sodium-fast reactors can also operate at low pressures, but they have reactive coolants that would be much too risky in a combat zone. You need a reactor that can take a lot of punishment and not risk a sodium fire or an supercriticality accident.
LFTRs can operate at high temperatures. This is important for generating power efficiently, but it’s even more important for making gas turbine power conversion (Brayton-cycle) and air-cooling feasible. With lower temperature reactors like water-cooled and sodium-cooled reactors, you have to use steam turbine power conversion (Rankine-cycle) and it’s really hard (not impossible, but really hard) to air-cool these systems without excessive penalty.
LFTRs are easy to fuel and keep running. Nobody wants to try to swap fuel rods or reprocess solid fuel elements in a remote environment. The liquid fuel used in LFTR can be shipped separately from the reactor. Don’t try that with a solid-fueled reactor. LFTR’s liquid-fuel is already in the right form for simple processing techniques like fluorination/reduction. Thorium in the blanket/shield of the LFTR absorbs neutron and gamma radiation while making new fuel to keep the reactor running.
LFTRs are stable and self-controlling. You don’t want a whole bunch of reactor operators trying to keep your reactor happy in a remote environment. You want a reactor that runs itself. LFTR can do that, through a strong negative temperature coefficient that makes it follow the load well, and the simple removal of xenon gas that would otherwise make changes in power level difficult. It’s the same reason why they wanted liquid-fluoride reactors for aircraft sixty years ago–they’re good at controlling themselves.
LFTRs can be protected against enemies. Liquid fuel means that “just-in-time” denaturing of the uranium-233 fuel is possible. If it looks like the bad guys are going to overrun your base, you hit a button and dump depleted uranium tetrafluoride in the core. Now no one will ever start your reactor again, and the U-233 is thoroughly denatured against any other use. (It’s always sad to trash U-233, but if the bad guys are coming, don’t you want to have the option?) Solid-fuel reactors can’t do just-in-time denaturing. You’ve got what you’ve got in the fuel and you can’t change it out in the field.
I spent two years as a civilian working at the US Army Space and Missile Defense Command, and had the privilege of working with men and women in uniform who had been over to the “sandbox”. I have talked with senior officials who have seen the problem firsthand that we face with vulnerable fuel convoys. I have talked to a general who wrote the letters to mothers and fathers telling them that their son or daughter had been killed transporting fuel through a combat zone. He had a simple question for me: would this reactor make a difference?
Yes sir, it would. It would make a big difference.