8.4 – The Isotope Separation plant and waste output

One other misconception on the internet is the view that a LFTR reactor will produce almost no nuclear waste, as the following You-tube video implies  (or see this “activists” banner here). This is not the case. All the while during the plant’s operating life that chemical plant will be producing nuclear waste material, and as discussed earlier some of that is pretty “nasty stuff”. Not a lot of it per day, but it all adds up! Also the supporters of the LFTR seem to assume that this CPP can operate with 100% efficiency (i.e remove all the radioactive poisons). This would be very technically challenging, especially in the LFTR case given the importance about separating out of U-232 (and its Thallium-208 payload) from U-233 or indeed removal of protactinium-233 as well as a host of other nuclear “poisons” discussed. Build up of these in the core both leads to increased irradiation of the core as well as the eventual shutdown of the nuclear reaction process altogether.

An CPP facility capable of that level of operating efficiency would likely be physically very large. Given that it will be working with radioactive materials, and the real radiological hazard is a pipe burst (an all too common occurrence and any chemical plant, and especially likely at these sort of working temperatures and radiation levels), we would thus need to put the CPP underneath our concrete containment dome. Obviously a large CPP will not only be expensive to build and maintain but greatly increase the size of this containment structure, further increasing reactor construction costs as well as increasing construction time (and reducing the number of said reactors we comission in any given time period).

And of course the supporters of the LF reactor concept have yet to come up with a functional design of an CPP. I’ve seen various dusty line drawings of the 1970’s ORNL proposal, you can see them yourself here and here, but that’s it. I would firstly note that materials science and chemical processing technology has moved on hugely in the last 40 years, so I doubt it would be sensible to build an CPP as shown in these plans. A new one would have to be redesigned from scratch.

The LFTR supporters have tried to counter this by coming up with designs of their own, but I’ve yet to see an actual working schematic, one that specifically discusses cycle efficiencies and above all else ENERGY INPUTS! The designers of this reactor seem to be assuming that this CPP, which will involve various stages of pumping, sparging, vacuum processing and filtering of the working fluid, often at a variety of set temperatures or pressures will operate with no net energy input and achieve 100% separation efficiency! In science we have a technical term for such a belief.

As the working fluid will be coming off the exhaust from the heat exchange cycle it will be relatively cool (in the MSRE it was at around 570 °C) yet some of these processing stages will require the fluid to be heated back up to 1,600 °C. Where’s that energy going to come from? We could use pinch technology and “pinch” (if you’ll pardon the pun!) some of that heat from our heat exchanger, but that has the disadvantage of yet more piping (and more safety risks!) and a reduction of heat exchanger efficiency. And this isn’t going to solve the issue of all the other kit I mentioned. Notably, the LFTR supporters have suggested (see here) using electrolysis to help improve the filtering efficiency of their plant. An excellent idea, it would solve a number of problems, but unfortunately electrolysis systems practically eat electricity! Where’s all that electricity going to come from?

Fortunately its probable some form of balancing point can be achieved in which we compromise the standards of our CPP, accept one that is smaller and less efficient (and thus our reactor burns much more fuel and produces more waste) but is sufficiently efficient to give us a decent fuel burnup rate without being over complex (or large), nor energy hungry. Of course exactly where this “balancing point” lies is the question and it would take some degree of research and experimentation to find out. Inevitably from time to time (probably at least once a year or so) we’d likely need to dump the entire core’s contents and replace it with fresh fuel. The “dumped” contents being added to the global nuclear waste stockpile.

Of course the wider economic problem with this CPP is the fact that we need to install and pay for a chemical plant right next door to our reactor, as well as pay staff to run it, buy in chemical feedstock and accept the fact that some of our valuable electricity coming out of the power station gets consumed on site. By contrast alternative record designs do not come with any of these costs, nor of course do fossil fuel plants nor renewable facilities. While nuclear waste output will be reduced, as with the GcFR we have to question whether the increased costs imposed by this CPP make it worthwhile, and whether we’d be better sticking with deep geological storage of waste.

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