Zone refining for Reprocessing

[Jones Beene]

This is a continuation of the previous thread regarding the prospect for an advanced, small, modular, safe and affordable nuclear reactor (rail mounted). My apology for another long post as I am aware that this subject is of limited interest to most readers - and that more than a few are ingrained anti-nuclear anyway. That is understandable. We have almost "blown it" for the past forty years.    It is a hybrid design which goes way beyond current thinking. It works ONLY when ALL the pieces of the puzzle are put together in a unit, as some of them individually do not look optimum. By my reckoning the current crop of so-called "advanced designs" are deficient in too many ways to mention - and are overly influenced by the entrenched and powerful special interests of the GE, Westinghouse, & the DoE "club." They are the problem, not the solution.   A key detail in how one can achieve nearly complete fuel burnup, starting with only natural Uranium, is in the absolute requirement for an ongoing (partial) reprocessing system which is built into the reactor itself.   This idea is not novel, but has been written-off for years, under the phony pretext of "non-proliferation" or mostly because partial reprocessing via the well-known technique of *Zone Refining,* (which is only "easy" technique) - this process only gets rid of the lighter fission ash and not the heavier poisons. Neither the military, nor the fuel suppliers like it, and it has been therefore "marginalized" by special interests.   When fission occurs, there are at least two molecules of "ash" which often are huge "neutron poisons" (high cross-section for thermal neutrons) and this inevitably dictates almost all of the subsequent design choices, and of course this usually eliminates natural Uranium as the choice fuel, despite its 10,000 to one net cost advantage (net meaning to society as a whole).    If it were not for these fission poisons accumulating, then we would never need to refuel the reactor, nor to store/bury old nuclear fuel - we could just burn it all, while fuel cost would be negligible, and most of the power for the USA would be nuclear already. The kicker is "heavy water"... but that is also becomes the beauty of the overall system. (more on that in a subsequent post). This being a forum where anything to do with deuterium is of interest, then even applying it to "hot fusion" should have some backing - not to mention that the very reason why it works so well (in part) - neutron stripping - is or can be related to ongoing electrolytic research.   In a later post, I am going to frame-up some basic speculation on the "next-step" in the evolution towards a more "active" heavy water moderating core, which uses 7-lithium and other LENR techniques to enhance neutron production..   IOW what I am saying is that the early choices, in the USA, to use enriched fuel and zero reprocessing and zero burnup of accumulated wastes - these terrible but understandable choices - have now almost doomed to the industry. In a perfect world, we should be getting almost all of our power from nuclear. It is the most ecological choice - done correctly. It is a terrible choice, done incorrectly. We are stuck in between and falling toward the incorrect extreme.   This past non-choice (regarding the possibility of partial reprocessing by zone refining) was due to the fact that historically, it was of negative interest to the military industrial complex. This is because they wanted to also segregate-out the fissile material, and also to get rid of the transuranics at the same time - which are no-good for bombs... and/or as for the companies like GE - this prohibits them form maximizing profits. Zone refining is contra-indicated for both poles of special interest, and was never pursued as actively as it should. The so-called neutron "poisons" are found on both sides of the density spectrum - and zone refining generally only allows removal of the low-density variety.   Had civilian power-producers been involved from the start they would have said - "WAIT" that is what I need - get your hand off my valuable so-called "spent fuel" (only 5% is actually "spent") and give me back this very valuable resource, and let me reprocess it for further use using zone refining - after all, I don't give a rat's-ass about transuranics. We will just burn them too."   This scenario never happened, and only a handful of reactor designers today even realize that if you provide an 1) unpressurized reactor (for continuous fuel removal) 2) natural U fueled-reactor 3) automatically controlled fuel removal and addition subsystem, and 4) continuous staged zone refining 5) lots of heavy water moderator   that essentially you can breed far more fuel than you burn, without "fast" neutrons (although some are helpful and can be designed into the concept) and also get nearly complete burn-up... and also put your toxic nuclear waste into an outer part of the reactor where it will be neutralized without quenching the criticality. Once criticality is achieved, all subsequent neutrons are "free," in one sense, and any reactor should be amenable to burning up its own waste. Then by this simple (but complicated) expedient of automatic and continuous zone refining, you can turn any reactor into a ideal breeder reactor but with the secondary problem that you deny special interests their huge fees for refueling and this concept is very threatening.   The key feature of this hybrid concept, then MUST include a closely coupled fuel-cycle in an unpressurized reactor for ongoing removal, purification, and recycling of the natural uranium fuel which ideally is in a liquid alloy or eutectic form, so that it can be removed by a "cold plug". BUT this doesn't not need to be "complete" reprocessing system, as is often envisioned. That is where the tonnage of heavy water come in. As for the Candu itself, it is not a true breeder - but goes part of the way there - getting its makeup neutrons largely from the moderator itself. If it had been designed to be unpressurized (say molten salt cooled or liquid metal cooled, then it could be amenable to the kind of minimal ongoing reprocessing I have mentioned above. This would make it a  into a strong breeder and allow 90% burnup.   It all fits together like hand-in-glove and consequently you have to start out the design process with the mind-set that you are going to either eliminate the steam cycle altogether, or to segregate the steam system - and power it with a secondary no-radioactive molten-salt heat transfer carrier. It is really impossibly difficult to safely depressurize and repressurize any reactor on a continuous daily basis for ongoing fuel removal and replacement. Note that this high-burnup scheme is based on continuous zone refining of only a portion of the fuel on a daily (night time) basis. You (robotically) remove - say 1-2 percent of  the fuel inventory per day and zone-refine it, in step one - taking off say 10% of the 1% and returning the rest with an added makeup. The reactor is operating all this while on lower than normal power.   Then...on a 24/7 basis, you are also doing the same type of zone refining with all of the accumulated ash laden parts of all the previous days - but in stages. Eventually you have gotten most of the less-dense ash out, based solely on density gradient, and returned most of the useable fuel,  even if it takes a few dozen stages. After all the initial ash content is only going to be in the few PPM. There is not as complicated as it sounds and there is little actual waste. This technology is NOW being used in the processing of semiconductor ingots all the time and you can purify to PPB levels. You never need a complete refueling. After a few years the reactor reaches an equilibrium state where the surplus of bred-fuel perfectly balances the stasis requirement for the burring-up of the retained transuranic poisons, and from there on - you essentially can burn a high proportion ~90% of the entire initial inventory. In theory ;-)   Do the national albs know about this? Of course they do, and occasionally it slips out in a patent application like Application # 20040062340, in 2004 for "Self-regulating nuclear power module"  LOS ALAMOS NATIONAL LABORATORY. Sooner or later some bureaucrat will cleanse this patent of certain language such as: "One of the remarkable advantages of this reactor concept is the novelty of the fuel form. The hydride chemistry essentially does an end run around many of the problems of nuclear fuel reprocessing. At the end of the useful life of the original charge of fuel, the module will be returned to the factory .... leaving uranium metal. This metal can be stripped of its fission product contaminants by simple zone refining."   We have known about this technique for forty years, kept it secret or marginalized it, and know that it will allow natural Uranium to become the best possible reactor fuel - plus allow complete burnup of all waste...yet??   For a fraction of the cost of the Nevada "crypt" we could have years ago nailed many problems with one solution. Why, then, has this technique been suppressed?   For that answer you will need to look at the balance sheets of GE and its minions who control the industry, and the approximately 50 billion in profits (in current dollars) over the past years from nuclear fuel reprocessing... which would have been reduced to zero - had power producers had any say-so in reactor-design from the git-go.   Who says politics and science don't mingle?   Jones