To add to this, even with the shielding provided by water in light water reactors, the neutron exposure is _the_ limiting factor for the reactor vessel.
The metric to look for is called "DPA" (displacements per atom), the number of neutron collisions that a material can tolerate before losing enough structural integrity to fall below the acceptable limits. The best modern reactor steels are at 150-180 DPA.
And a lot of potentially cool reactors like TWR (travelling wave reactor) end up being logistically impossible because lifetime-limited components will be exposed to multiple hundreds of DPAs.
Many old LWR's have had their reactor vessels heat treated during a maintenance break to undo some of that neutron radiation damage and extend the life of the reactor.
Not sure whether it would be possible to do something similar to a liquid fueled reactor, including all the hot pipework. Maybe, but yet another cost. Notably some of the recent MSR projects propose replacing the entire reactor every now and then (Terrestrial or whatever they were called, not sure if they are still around).
Yes, it's called "annealing". Basically, the core is de-fueled and a huge electric resistive heater is put inside it. Then the entire vessel is heated to something like 600C, and kept there for several days.
It helps the atoms displaced by neutron collisions to "snap back" into the correct places in the crystalline structure. But it can never restore the material completely, and over time the annealing breaks will have to be more and more frequent.
It also can't be used for everything. Some pipes will experience large thermal stresses if annealed, and some components can't be heated properly due to complex geometry.
As with everything in engineering, all problems can be solved with additional complexity. It's possible to design LFTR reactors to be more annealable, but it will likely make them impractically complex.
There are also other issues with LFTRs. A significant part of the energy production will happen _inside_ the pipework carrying the molten salt, as delayed fission happens and daughter products decay. This will cause inevitable problems with the reactor power control.
Modern light water reactors are engineering marvels. They are incredibly compact for the amount of power that they generate, and they are now designed with the anticipated 70-100 year operating lifetime. Getting LFTRs to the same level of maturity might be possible, but it'll require literally hundreds of billions (if not trillions) invested, just like with the classic nuclear.
You are describing "dry" annealing there. This has not been applied anywhere, as it requires removing and reinstalling the internal support structures inside the reactor vessel.
A somewhat lower temperature "wet" annealing process has been applied to two test reactors. I don't think it's been applied to any full scale power reactors.
I wonder if it's possible to run it hot enough for the radiation damage (basically a bunch of dislocations, right?) to just anneal itself out continuously, like how Wigner energy is dissipated in graphite when it's hot enough.
No, this is fundamentally impossible with steel. Annealing works by making the material more "plastic", and this necessarily reduces its tensile strength. Which is the limiting factor for the vessel.
You can make the vessel thicker to compensate, but then you can just make it thicker in the first place and skip annealing.
The metric to look for is called "DPA" (displacements per atom), the number of neutron collisions that a material can tolerate before losing enough structural integrity to fall below the acceptable limits. The best modern reactor steels are at 150-180 DPA.
And a lot of potentially cool reactors like TWR (travelling wave reactor) end up being logistically impossible because lifetime-limited components will be exposed to multiple hundreds of DPAs.