but it was believed that some small change in the formula such as adding Niobium could clear the problem up. What's needed to move forward is not a big conceptual breakthrough but rather testing of materials under realistic conditions... A new test reactor.
What is more problematic with the MSRE design is that it incorporates graphite as a moderator and the graphite swells and goes bad over time. Possibly you can take the graphite core out every few years and replace it with a new one, but people have also found designs that don't require a moderator outside the fuel salt.
When I went to the first conference on Thorium Energy years ago David Leblanc had done some very simple calculations that showed you didn't need the graphite -- it works just fine with a faster spectrum. He's refined that idea and is running with it. Others are pursuing chloride salts and plutonium fuel with a very fast spectrum.
Fast spectrum MSRs bring a whole litany of other problems. Chlorine has more oxidation states and the chemistry with fission products is much more complex.
Starting with graphite makes sense imho for a university.
If it's designed with replacement in mind, a graphite moderator isn't all that bad. It can even be a safety advantage, in that if you drain the fuel out of the vessel it's taken away from its moderator.
I'm not a nuke physicist, but I recall LFTR presentations on the "safety plug" to stop meltdown: basically a plug melts and the fluid flows into a shallow pool.
Since the fluid is "thinned", neutron economy plummets and chain reactions stop.
In addition, I though the fluid would expand a bit under high heat in the reactor, which would drop neutron economy as well, so a fluid can somewhat self-moderate.
So unless the fluid is in a ball or tank where the neutron economy is maintained in three dimensions, if you drain it out it no longer has the neutron economy.
So what they probably are saying is that since the fuel is fluid, and if you need to replace the moderator, you drain the fuel (and as stated above, that stops the reaction as well) and replace the moderator.
If the fuel is designed such that it needs a graphite moderator to sustain a reaction, then if the fuel is removed from the reactor it's less likely to go critical than if the fuel was "higher-grade". It's less likely to have a criticality accident.
A moderator is a material that slows neutrons down. Slow neutrons are more likely to initiate fission in a Uranium (or other fissile) nucleus that they hit, so a moderator increases the reactivity of the reactor.
https://haynesintl.com/docs/default-source/pdfs/new-alloy-br...
(which is practically stainless steel without the steel) was good for this use but when it was tried in this system it did not hold up very well
https://en.wikipedia.org/wiki/Molten-Salt_Reactor_Experiment...
but it was believed that some small change in the formula such as adding Niobium could clear the problem up. What's needed to move forward is not a big conceptual breakthrough but rather testing of materials under realistic conditions... A new test reactor.
What is more problematic with the MSRE design is that it incorporates graphite as a moderator and the graphite swells and goes bad over time. Possibly you can take the graphite core out every few years and replace it with a new one, but people have also found designs that don't require a moderator outside the fuel salt.
When I went to the first conference on Thorium Energy years ago David Leblanc had done some very simple calculations that showed you didn't need the graphite -- it works just fine with a faster spectrum. He's refined that idea and is running with it. Others are pursuing chloride salts and plutonium fuel with a very fast spectrum.