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Some nukes are better than others

Page history last edited by Andrew Alder 2 years, 7 months ago

A page of energy issues. See also nuclear homework.


Some nukes are better than others. Here are some examples. It's not a complete list, but it should give some food for thought. Like much of the web it is an evolving page and is becoming more complete with time.


And some of these headings overlap. I know! But I hope it will prove informative even so.




The good



Many in operation.


Oxide fuel, either slightly enriched Uranium or MOX. Ordinary water cooling and moderation.


One serious accident, Three Mile Island, in which the melt didn't escape the pressure vessel. There was secondary containment, as in all modern PWRs, but it wasn't needed.


Some Soviet-era PWRs (called VVERs) have no secondary containment, and it would be good to close these even so.


Safe. Can't be used to produce military material, see fool grade, and ideal candidate to support the NPT. Waste a solved problem.


The most promising recent SMR proposals are PWRs. After much thought I've decided to list them as SMRs rather than PWRs, so they're discussed as Ugly below, but it's maybe a line call.



One prototype, EBR-2, operated and produced power for many years. The best fast reactor power station yet, and radically reduces the amount of fuel required and the amount of waste produced compared to a PWR. The best solution to the waste a PWR produces, in fact, as it can burn the leftover Uranium and Plutonium and other transuranics from spent PWR fuel, and these tend to be the longer-lived radionuclides in this waste, spectacularly so if you count the unused Uranium, 


Metallic fuel, a "starter" charge of enriched Uranium or other fissile material needed at first startup but from then on almost any fissile or fertile material can be used, notably spent PWR fuel as noted above. Sodium cooled, three levels (primary and secondary coolant and a unique fuel design providing a third level). No moderator, it's a fast reactor. 


Proliferation issues, yes, but relatively small compared to other fast reactors and to fusion plants. Ideal candidate to support the NPT


It is time to build EBR3.


The bad



Proposed cladding failed. Not tested before significant commitment to the program. 


Originally planned to use natural Uranium fuel but in practice enrichment proved necessary owing to the cladding problem, which destroyed the economic case for building it.


Britain's second costliest mistake post-war, at least. The other candidate for first place is the Concorde.  



Unstable. That was publicly predicted by Western experts and acknowledged by the Soviets before it was built. See The upside of Chernobyl.


And yet, did you hear a single word of criticism of the design before it blew up? Where were the greenies? Oh, they had more important things to do, like chanting slogans outside PWRs and telling the public barefaced lies about Plutonium. See sex lies and nuclear power.


One serious accident of course, Chernobyl.


Ordinary light water cooling, graphite moderator, oxide fuel. Originally planned to use natural or even depleted Uranium fuel, such as spent PWR fuel. See why on earth did they build the RBMK.


Ten still operating as of 2020, the last to close in 2034, but with enriched fuel to remove the instability. But that also removes the economic justification, so all subsequent construction and the proposed successor the MKER cancelled.  


The ugly

 Many candidates. Some may yet prove to be ugly_ducklings. Others will remain ugly.



One of my pet peeves. Nuclear engineers love them. Two serious accidents, SL-1 and of course Fukushima.


No secondary coolant. The irradiated primary coolant goes through the turbines, as with the RBMK and SGHWR. This limits containment possibilities. See why on earth did they build the BWR.


There is some hope. Britain has quietly cancelled plans for two BWRs (ABWRs actually) while proceeding with their planned PWRs. Germany is closing every nuke but closed their only BWR first of all.


Japan is in the process of restarting their PWRs and it now looks as if they will also restart their remaining BWRs.


So it would seem that some but not all people would now list the BWR as "bad" rather than "ugly", and they have a point. Not as bad as some but certainly not good.



Unsolved waste problems. Enormous in scale. Proliferation issues. Hyped. Proposed implementation always ten or more years in the future. My prediction is in the range AD 2200 to AD 3000. The reason for this is, it can't compete with PWRs and IFRs for a long, long time. It has all the same problems, but in each case worse, and no redeeming features apart from those in science fiction.


The main reason for its ugliness is the misinformation surrounding it. People say that with fusion there are no issues with bombs, wastes and accidents. Wrong, wrong and wrong, respectively. People (most recently the Chinese promoters of their latest little tokamak) say that they are using the process that makes the Sun hot. Wrong. That reaction is too slow to work in anything smaller than a star. They and everyone else are using the reaction that makes a thermonuclear bomb explode. 


And it goes on and on. See myths of fusion and materials for fusion reactors.


Or to look at it another way, there are two widely believed myths surrounding fusion. One is that it's a good idea. The other is that it's likely to happen soon if enough money is spent on it. There is no evidence to support either of these beliefs, and they are a dangerous combination. 



There are two very different classes of reactor sometimes called MSR. 

  • Molten-Salt_Reactor_Experiment or MSRE used molten salt that contained the fuel, see also LFTR for other proposed designs.  MSRE got as far in 1965 as ITER hopes to by the end of the experiments that will start in 2035. So not the ugliest by a long way! 
  • Other designs use molten salt only as coolant, see molten_salt_reactor


Both have their advocates, but many of the advocates of the MSR do not even seem to know which of the two they are recommending, if they even know that there are two.


It should also be mentioned here that there is a third proposed type of reactor that uses molten salt and is therefore called an MSR by some. The Natrium reactor is sodium cooled but uses molten salt as the secondary coolant. This molten salt is then used to boil water, and also for energy storage. It's a very interesting design, but it's not really an MSR. The molten salt has nothing to do with the reactor core.



Even more various and popular than the MSR, and they have in common with the MSR that many advocates don't know what sort they mean. Or if they do they are careful not to say.


All SMRs can also be called something else depending on the technology used. There are little MSRs, little gas-cooled designs such as the PBMR, and the Americans built a little BWR. There have been little fast reactors in submarines, cooled by various liquid metals. Some of these were not very successful; The only American one, the S2G_reactor, was quickly replaced by a PWR. One of the Soviet ones was cooled by an alloy of mainly separated Lead, which is probably the ultimate fast reactor coolant.


Some do show promise.


Probably of most interest, there have been many small PWRs and more are proposed. Listing them as ugly was a line call as I said above. These little PWRs are based on technology proven in naval propulsion and in large power stations. The only reason for not calling them PWRs is political. A week is a long time in politics, and the honeymoon with some greenies may not last when the time finally comes to build one. Or alternatively, it may even give some of them a way out, see the green nuclear backdown.


But that's not the best reason for preferring them to full-sized PWRs, is it? It's that political manouvre that qualifies them as ugly IMO. 


See a recent French proposal here, a British one here and an American one here. A diagram of the American proposal is here.


Small power station PWRs are not a new idea. The US Army_Nuclear_Power_Program was mainly small PWRs, all of which were reasonably successful, while their other designs were not so successful, including of course the BWR that blew up, and some molten salt experiments. The Russian floating nuclear power plants are each powered by two little PWRs based on naval reactors.  


So PWR SMRs have long had niche applications and continue to do so. The question is, does a fleet of many little PWRs really have any advantage over one of fewer full-sized PWRs? That's the claim of the PWRs that are also SMRs. Time will tell.  




TerraPower designs

Two interesting ones, the Travelling Wave Reactor was the first but seems to have quietly dropped from sight. The more recent Natrium Reactor has sodium primary coolant but molten salt secondary allowing energy storage so the reactor can run 24/7 but the turbine can be greater capacity than the reactor.    



The three proposals for MSR SMRs from MOLTEX, called SSRs, deserve a hearing. I don't think they will replace the PWR, but they might even replace the IFR. Too soon to tell. 


They have an extra stage of liquid inside the fuel elements, like the IFR, but this liquid is molten salt fuel like MSRE rather than molten sodium coolant like EBR2. The SSR-W has a fast neutron spectrum and can consume spent fuel from other reactors. Very interesting indeed.  


Magnox and UNGG

The UK and France both built dual-purpose plants, Magnox and UNGG respectively, to produce both weapons-grade Plutonium and electricity... not both at once, but either option depending how the plant was operated. Both had natural Uranium metal fuel, graphite moderator, and gas cooling. 


To produce weapons-grade Plutonium you run the reactor at low power and refuel it often. To generate electricity you run it at high power obviously, and to do so economically you refuel it less frequently. And you might as well, as the fuel irradiated at high power is useless for bombs anyway. 


The UK later built larger Magnox reactors dedicated to electricity production. These were superseded by the unsuccessful AGR project. France went on instead to build a fleet of PWRs. Some of the Brits now wish that they'd continued with more Magnox plants, and it's an interesting speculation but that horse has bolted. The latest British power reactor is a PWR, and several others are proposed or planned. (Two proposed ABWRs have however been cancelled.)



Canada developed a unique and successful design using heavy water moderation and natural Uranium fuel as oxide, the CANDU. This was at least partly motivated by their heavy water expertise and capacity developed for the Manhattan Project. Uranium enrichment technology and capacity, on the other hand, was jealously kept under US control.


While designed primarily for natural Uranium, the excellent neutron economy allowed a wide variety of fuels to be used.


Development is continuing. But each successive generation looks more and more like a PWR. The latest CANDUs use light water cooling and heavy water moderation, unlike earlier designs that used heavy water for both. This reduces the heavy water inventory, a major cost, to about one-third of that required for the earlier heavy water only designs. But this has also required slightly enriched Uranium fuel.


SGHWR and similar

The SGHWR was heavy water moderated, light water cooled, water boiled in the core like in a BWR or RBMK. Able to use a variety of fuels, including natural Uranium, as oxide.


One built, in the UK, the Winfrith Reactor which successfully generated power for the grid from 1967 until 1990. A possible export order for Jervis_Bay_Nuclear_Power_Plant fell through when that project was cancelled, with South Africa also interested had that order gone ahead, but the design went no further.


There was one experimental power reactor in Canada at Gentilly_Nuclear_Generating_Station that was called a CANDU but was similar in concept, one in Italy called CIRENE, and one in Japan at Fugen_Nuclear_Power_Plant, but those designs went no further either.


Other Thorium reactors

India and China are spending significant amounts of money developing the Thorium (or more properly Thorium/Uranium or Th/U) fuel cycle. Thorium is more abundant than Uranium, and India in particular has lots of it. But there are several obstacles to rolling it out anytime soon. Here are just the two most obvious.


Firstly, the Th/U fuel cycle depends on the Uranium/Plutonium (or U/Pu) fuel cycle to get started. U-233 is created by irradiating natural Th-232 in a reactor. But that reactor needs fuel. The only natural fissile material is U-235, mined as Uranium of course. In order to "breed" U-233 from Thorium, you need a fuel for that reactor. Uranium and Plutonium are the only real possibilities. 


So India is for the moment concentrating on U/Pu to build up its inventory of fissile material (Plutonium in this case) with the declared intention of switching to Th/U as soon as possible.


Secondly, Th/U has a lot of catching up to do before it's a serious rival to U/Pu. The U/Pu fuel cycle, including but not only Uranium enrichment and Plutonium production, was developed for the Manhattan Project. The PWR was developed, based on this research and infrastructure, to power naval vessels. Military money paid for it all.


(But note that while this military research and infrastructure supported and influenced the nuclear power industry, it has never yet been the other way around. Yes, I say that a lot!)


And perhaps you can now see why the Manhattan Project did choose U/Pu and virtually ignored Th/U. It was simply that they were in a hurry.


Other Generation IV reactors

The phrase Generation IV reactor was coined by the founders of the Generation IV International Forum or GIF. The GIF promotes a disparate range of proposed designs, some of them already mentioned above, see  Generation_IV_reactor#Reactor_types.  





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