My last post on however came to negative conclusions about the graphite moderated two fluid reactor design. I knew that Kirk Sorensen probably held differing views, but Kirk has yet to demonstrate that he can solve the problem raised by David LeBlanc.
Yesterday Kirk posted a new discussion of the two fluid graphite moderated reactor, this one based on research being conducted at the Nuclear Research Institute at Rez in the Czech Republic. Czech researchers Jan Frybort and Radim Vocka have taken another look at the ORNL-4528 type reactor using contemporary computerized reactor research tools. Their findings, reported in a paper titled Neutronic Analysis of Two-Fluid Thorium Molten Salt Reactor. Kirk suggested.
In part 7 of the paper, they mention the second key issue with a two-fluid reactor--the problem of the blanket void coefficient. Since the original ORNL design had the problem, and since they modeled only parametric variations on that original design, it's no surprise that the problem still shows up. It must be fixed, probably through a new design approach to the two-fluid reactor. I have some ideas, most all of them based around physical situations where a loss of blanket fluid leads to a loss of moderation. I anticipate that this could be done by floating moderator elements (graphite) in the blanket salt, so that as the level of the blanket salt falls, the moderation decreases more than the absorption decreases from the loss of blanket. These ideas definitely need more modeling, but I think they are essentially sound.Thus Kirk believes that a different approach to the graphite design might work, and that he himself might hold the solution. Kirk has concerns about patent rights, so he is reluctant to say too much. Thus it is too soon to write off the graphite moderated two fluid reactor yet, but we two fluid reactor that is need to have an alternative available. Fortunately David LeBlanc has designed an unmoderated two fluid reactor which has a very simple and low cost core. Thus David's reactor design would serve as an acceptable, easy and cheap to build alternative to an ORNL-4528 type reactor. Kirk, unlike David LeBlanc, is unwilling to write off the graphite moderated two fluid reactor yet.