Post by David B. Benson on Apr 24, 2019 17:49:34 GMT 9.5
High-fidelity simulations point the way to optimizing heat transfer in current and next-generation reactors Leda Zimmerman 2019 Apr 23 Phys.org
offers an article on bubble formation on the surface of nuclear reactor core elements. Bubble formation without prompt removal seems to be very bad as far as I know. I can't say that I understood this article.
This does explain the interest in supercritical water reactors and non-water coolants. Going supercritical eliminates boiling altogether (there is a continuous change in density with temperature, not a phase transition) and non-water coolants like sodium and lead push the critical heat flux to new highs without pressurization. (The EBR-II achieved a thermal output of 65 megawatts from an active core zone less than 5 feet across.)
CFD has been used for some time for all sorts of nuclear heat transport problems. Until recently there were quite large uncertainties, but improved software and more powerful hardware means that a "brute force" approach to simulate what is actually going on is now largely possible. Experiments to validate the results are still key, though...
Enhancing the surface where boiling/heat transfer occurs is a good way to improve performance. For example, here is a company that supplies enhanced "dimples and pimples" that improve turbulence. It seems to work even better for boiling processes because of the nuclear site enhancement. They are talking about, in some cases, over a 100% improvement in the heat transfer coefficient. If applied to nuclear fuel rods in say a BWR or a SCWR that would be an enormous improvement. Power uprates would be possible that would make Lightbridge fuel look tame.