8.2 – The MSR Experiment

Firstly, there is a view that the LFTR concept has been “proven” already via the Molten-Salt Reactor Experiment (MSRE) project in the 1960’s. While it is certainly true that such a reactor ran successfully for 4 years and that this project proved that some of the ideas behind the MSR have merit, there are a couple of key things it didn’t do. Notably, it never generated a single watt of electricity. As I’ve mentioned previously the turbo generator systems for high temperature reactors is technically challenging, especially for the LFTR as the molten salt presents a number of design challenges.

The ORNL Molten Salt reactor experiment of the 1960’s

That said, the goal of the MSR experiment was to prove the reactor concept, not develop turbo machinery kit, which would have been a serious (and costly) distraction. The molten salts at the MSRE were passed through a cooling loop and fans used to blow the pipe work cool again. Stories of said pipe work glowing red (see below) are worrying, as it indicates they were operating well within the thermal creep zone. At the time very little was known about thermal creep, in particular the delirious effects of neutron bombardment on exacerbating the problem. Consequently, its unlikely one could utilise the same design spec today for a commercial plant. Indeed, reports of distortions in the graphite moderator after just a few years exposure and worse  inter-granular cracking (a corrosion related failure phenomenon usually caused by excessively high temperatures) of some metal components exposed to the molten salt, suggest it was operating well outside the limits of what would count as a reasonable safe technical envelope (at least for a commercial reactor with a long operating life). As I will detail later this has significant design implications. The reactor also spent a good deal of its time down for maintenance.

The cooling circuit of the MSRE glows red hot due to its high operating temperature

Also, the MSRE never included the more tricky Chemical Processing Plant. One was designed by ORNL but never installed. Aside from using a chemical spray technique to separate out the more nasty neutron “poisons”, such as Xenon-135, much of the remaining “chemical plant” functions of this reactor design have never been tested. While the MSRE did run once on U-233, this was generated off site, not by the reactor itself. Finally, as I hinted earlier, 40 years is a long time. Very little of the technical side of building this reactor would be relevant today given how much technology, especially material science has changed. Many of the scientists who worked on it are either dead or retired. While one won’t be starting off with a blank sheet of paper, you probably won’t find yourself far removed from that.

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