Also, that they avoided graphite and used hex boron nitride instead.
Fast spectrum reactors must not have lots of materials with atomic numbers under 16 in them. The lower the number the better the neutron moderation effect measured in Barns. Hydrogen is the best, lithium, carbon and nitrogen all are also great moderators which must be avoided to keep the spectrum of the neutrons above 100ev. Fast spectrum reactors have the ability to breed more fuel than they use with U238 being fertile in a fast spectrum in addition to being fissile at the very hard end of the fast spectrum. Barring ocean uranium recovery which is in the lab stages today the World uranium reserves will only last 36 years if nuclear power was to replace fossil fuels in a 50% rate less if they replace 100% the math works out that if the world builds 6000 one gigawatt scale reactors of PWR , BWR or thermal spectrum gas cooled which would replace 50% of primary fossil fuels use on a direct BTU to BTU basis the world runs out of uranium in 36 years. Using high converter reactors such as CANDU heavy water reactors with a conversion ratio of .8 vs .6 for PWRs extends that time to 58 years.
Thermal reactor by their physics can only use 0.7% of the energy in natural uranium in a once through throw away cycle that the USA is forced to use. France and Japan reprocess their used fuel into MOX but again in a thermal spectrum GWD/THM is under 1.5%. Only fast spectrum reactors can use 100% of natural uranium energy content with reprocessing even a once through breed and burn cycle would approach 40% fission consumption of heavy metal in place. That’s at least 40 times the length of time or centuries of power. With integrated reprocessing that extends to millennia with not a single gram of newly mined uranium the amounts in storage around the world today will drive fast reactors for thousands of years with integrated reprocessing. This natirum reactor is the logical next step in nuclear power. Sodium is well suited for fast spectrum reactors, it has high thermal mass and a high boiling point so in a pool reactor there is no risk of loss of coolant by venting or boiling. Sodium also keeps the spectrum very hard allowing breed gains of up to 1.8 no other fluid comes close to that breed ratio. That means every fuel cycle nearly twice as much fissile fuel is created than is consumed generating power. One reactor in its 60 year life will spawn a daughter of equal size every 8 years or less. The reactor can and is passive safe with natural convection decay heat cooling. By removing the steam cycle and putting in inert salt then removed the one flaw of sodium it burns with water in the tiniest amount. Having salt next to sodium eliminates that issue completely. The pool itself is under triple layers of concrete and stainless steel with helium and argon cover gases. Molten sodium is handled in the millions of tons by industry every year it’s a well used and valuable industrial metal. The salt itself is not water soluble so in the event of a salt to steam generator break water cannot contaminate the salt. At 600+C you should not be using steam generator at all at those temps supercritical CO2 brayton cycles are 20% more efficient than Rankin steam cycles. CO2 being inert to the salt as well as molten sodium. They are using steam simply to repower the existing coal plants turbines on the cheap. A Greenfield project should use supercritical CO2 turbines which need no liquid cooling they use dry tower heat sinks so desert use is not limited by water for cooling. SCO2 also heat dumps at above 100C at the tail end of the turbine train this is perfect temps for vapor compression desalination tech.
Fast spectrum reactors are a must for the future of humanity. Unless fusion becomes a net energy producer in the next 30 years fast spectrum will be needed. Fusion hybrids make sense as well use the 14Mev neutrons to drive a uranium blanket into fast fission and breed huge amount of PU for use in daughter reactors. UT Austin has a design for a fusion fission breeder that could power 15 daughters with it’s fuel output all being 1 gigawatt electric in size.