All devices have failures. We have to consider the possible failure methods of any nuclear reactor design.

We don’t know the ways LFTRs would fail, just like we didn’t know decades ago that a 9.0 earthquake and tsunami could knock out all diesel backup generators leading to loss of coolant accidents, or how engineers’ recommendations would be ignored in construction of sea walls, at Fukushima-Daiichi.

But we do know many ways that current reactors fail that LFTRs can’t — we know LFTRs can’t fail from core meltdowns, loss of coolant, or high pressure explosions.

Components that fail, or that sensors detect are out of specifications, would be replaced. Molten fuel that can be easily drained from the reactor, and atmospheric pressure, make replacing components easier than in LWR. Multiple small reactors supplying a region, all normally operating below peak, would eliminate power disruption during maintenance.

Since LFTRs could be mass-produced and installed everywhere a 100MW – 1000MW power source is needed, small problems such as leaking pipes would be much more frequent (though less likely per gigawatt).

Current reactors have leaking pipes, often. Easy to detect, easy to fix, easier to clean up in a LFTR since radioactive material is trapped in a salt that cools to a solid, instead of leaking radioactive water. At atmospheric pressure and with chemicals that don’t react to air or water, repairing the pipe would be the same or easier than for a solid-fueled reactor.

Fire a cannon at it, and the fuel would spill out onto the building floor and collect in the drain tanks. Damages the reactor, you’d have to repair it, but not a radiation disaster. Loss of electric power generation would be annoying to the city; but most cities would have multiple smaller reactors instead of one larger one.

LWR needs fuel for 18 months, so need to have “excess reactivity”. Since all MSRs can be fueled daily (or even continuously), the amount of uranium and all other radioactive materials in a MSR at any time would be less than in any solid fueled reactor. For a LFTR there would be no radioactive fuel stockpile (thorium is pretty harmless unless ingested). No MSR has “spent fuel storage”, just short-term storage of fission products (83% of them are below background radiation in under 10 years).

(MSRs designed to consume LWR spent nuclear fuel would be located at the waste storage facilities, which are heavily guarded.)

“MSRs will have an increased potential [compared to solid fuel reactors] for small-scale radioactive materials leaks because the highly radioactive fuel material is liquid and comparatively more accessible than solid fuels. The leak probability will be increased for on-line reprocessed reactor design variants as a result of more intensive fuel salt manipulation. The fuel salt reprocessing manipulation will need to take place within a hot-cell type environment, providing an additional containment structure within the primary reactor containment.” Fast Spectrum Molten Salt Reactor Options, Oak Ridge National Laboratory, July 2011

(MSR leaks would quickly cool to a stable solid, rather than the radioactive water leaks in a water-cooled reactor.)

Terrorists with plastic explosives, to send radioactive fuel droplets into the air? They would quickly cool to glass-like solid, wouldn’t stay in the air (too heavy, about 2.4kg/liter), wouldn’t dissolve in water, wouldn’t flow well in water, but of course would have to be collected. Since there is much less radioactive material in a LFTR than a PWR, just enough fuel to sustain fission, and radioactive fission byproducts would be regularly removed, there would likely be injuries only for people close enough to be hit by explosives spraying shrapnel and hot liquid salts. Installing LFTRs underground would make placing those bombs much harder to do. Put the electric turbine above ground, and in tours of the facility call it “the reactor” so most terrorists would strike the wrong device.

Insiders who have access to the reactor, and can install some high-tech “fire hose” that would handle 700° C highly radioactive liquids and gamma rays, for at least a few minutes?

There would be heat burns from very hot liquid hitting people. I don’t know what happens if radioactive FLiBe gets inside you, from drops landing on you; seems that would be the worst. So we would want to protect the facility against people installing explosives or other things.

Looks like the point terrorists would target is the attached equipment to use heat, air and CO2 to make methanol and gasoline; “It’d be like blowing up a big tank of gasoline, we’d get a big ‘splosion and be in the news!”. There would need to be an above-ground truck loading station or gas pump, easy to attack. Of course, the reactor would be shut down, and methanol/gasoline production would cease.

There are dozens of terrorist targets that would be easier and less expensive to attack. It’s easier and more dramatic to blow up a school bus or bridge or restaurant. But we still have to look at ways to prevent attacks.

Since all MSRs could be factory assembled, sensors for security and reliability can be installed throughout the reactor. These could communicate security status via satellite, electric power lines, local alarms. Tracking devices can be in each component, each batch of fuel, each batch of fission products. Molten Salt Reactors can be extremely difficult targets for theft or terrorists.