Comment on “critical analysis of future nuclear reactors designs”

About two weeks ago I left this comment on a blog critical of Molten Salt Reactors and other designs. So far the author has not published the comment, so I’m plopping it down here for future reference.

While Part 8 gives some good information that LFTR proponents ought to know more about, I spotted it being used in an anti-nuclear article called “13 Examples of TED talks nuclear neoliberalism” by some guy pretending, or possibly believing, that a sodium-cooled fast-breeder reactor is pretty much the same thing as a thermal-spectrum molten salt reactor, so that if a research program for the first failed, surely MSRs are doomed. And his source was Part 8 of this blog.

I mean, gee, “reduce your sodium intake” means “reduce your salt intake” so the words must mean the same thing, right?

Anyway, you’ve asked us to keep it brief so I’ll comment only on the beginning of Part 8 and then stop.

My main concern about your article is that you mention a lot of potential problems, but you don’t appear to have done any research to find out whether the problems have already been solved. Many LFTR supporters could be accused of “motivated stopping”, the behavior of avoiding looking for new information once you’ve reached a conclusion you like. LFTR supporters stop once they learn the benefits of LFTRs; you could similarly be accused of ending your research upon learning about potential drawbacks.

“As I’ve mentioned previously the turbo generator systems for high temperature reactors is technically challenging”

Aren’t you aware that MSR designers have no intention of designing turbines for their power plants? Thorcon, Moltex and Terrestrial Energy all intend to create nuclear islands that produce hot, clean, non-radioactive molten salt (typically solar salt) as their output, not electricity. This salt will travel outside an isolated nuclear zone into another zone that typically contains conventional turbines of the same sort you would find in a oil/gas/coal plant. The solar salt is isolated from the fuel salt by at least two heat exchangers.

The design goal is that nothing that happens to the salt after it leaves the nuclear island can cause a safety hazard. For instance, designers would ensure that if the salt fails to be returned to the nuclear area, or if the salt is somehow contaminated when it returns, or if there is overpressure caused outside the nuclear zone, none of this would be a safety hazard.

“Stories of said pipe work glowing red (see below) are worrying, as it indicates they were operating well within the thermal creep zone.”

All three of the MSR companies I mentioned intend to keep the fuel salt below 704°C at all times. The output salt temp (at the edge of the nuclear island) varies by company but likely won’t exceed 600°C. I’m no metallurgist but surely there are modern materials that handle such temperatures easily, and I think we can take it as a given that MSR designers are not stupid.

“reports of distortions in the graphite moderator after just a few years exposure and worse inter-granular cracking”

That’s a different topic than the piping, but it is a well-known problem for everyone involved. Moltex opted for a fast reactor to avoid graphite entirely; Terrestrial Energy deals with the problem by making their reactor cores affordable enough to replace every seven years, and Thorcon similarly plans to use cores for only 4 years and then go through some kind of retrofitting that they don’t talk about much.

I haven’t heard about this cracking issue but a quick web search fingers tellurium as the cause and a search for “tellurium cracking molten salt reactor” shows various research results. It sounds like the discovery of the problem led to successfully finding a solution reported in the 1977 paper “Status of Tellurium-Hastelloy N Studies in Molten Fluoride Salts” whose abstract says “The intergranular embrittlement produced in HastelLoy N when exposed to this chromium telluride-salt mixture can be reduced by adding niobium to the Hastelloy N or by controlling the oxidation potential of the salt in the reducing range.” I’m no chemist either (are you?) but it sounds like a plan.

“even Thorium-232 is a problem with its half life of 14 Billion years”

That’s an amazing thing to worry about. Thorium-232 is a material that was taken out of the ground. If it wasn’t a safety concern when it was in the ground in the first place, why does it suddenly become a safety concern if you put some of it back into the ground later on?

“The UK based NNL (National Nuclear Laboratories) also pour cold water on the idea of Thorium fuelled reactors (see here). While the report is low on detail (they seem to be saying “trust us we’re scientists who work with nuke stuff… and we smoke pipes!”) they do highlight the major time delays it would take to establish and get working a Thorium fuel cycle (10–15 years with existing reactors, 30 with more advanced options), point out that under present market conditions its unlikely to be economically viable and will (as the points above raise) offer only a modest reduction in nuclear wastes.”

That link is broken, but do I infer correctly that you’re referring the 2010 position paper titled “The Thorium Fuel Cycle: An independent assessment by the UK National Nuclear Laboratory”, presently in the Google cache here?

That article is often cited by anti-nukes as an argument against LFTRs. The abstract doesn’t say so, but the article itself is clearly not talking about LFTRs or MSRs, it is talking about thorium in solid-fueled reactors (LWRs and HTRs). The words “molten”, “liquid” and “salt” never appear, as though the authors had never heard of them, so why would you act as if the article is an argument against them? MSR supporters agree that there’s little reason to use thorium in solid-fuel reactors. Plus, MSRs don’t necessarily contain thorium and the main benefits of LFTRs come from the molten salt rather than the thorium.