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fool grade

This version was saved 3 years, 7 months ago View current version     Page history
Saved by Andrew Alder
on November 6, 2020 at 10:08:26 am

Being something of a fan both of Wikipedia and of the Integral Fast Reactor (IFR), I drop by that Wikipedia page every once in a while to see what the latest lies are that have been added to the article in an attempt to discredit the concept, or at least to try to explain why it hasn't been pursued.


There are a few standard ones. And one of the more common is a fascinating story. I hope you find it a good read.


Please note, I'm not for one moment saying that all those who spread this lie are deliberately lying. I've spoken to them. Most of them just don't know their stuff.


(If you think you do and/or would like to you might find my nuclear homework page helpful,) 


So read on, and you may get some surprises. It's a fascinating subject, and a fascinating story.




But first a little terminology

There's a lot going on, and even within the industry the meaning of what seems like a technical term may depend a lot on the context in which it is used.


And in particular, the term LWR is ambiguous. It has a very broad meaning and a far narrower meaning, and it's the narrower meaning that is used in the quote below from Wikipedia, and that's the meaning that will be used below. In the narrowest sense, an LWR is a type of power reactor, and more specifically it means either a BWR or a PWR. In the broader sense,  the term can include many other reactors (but not the IFR, interestingly, and we will come to that).  


A power reactor is one whose purpose is to produce heat, as opposed to one whose purpose is to produce Plutonium or industrial or medical materials, or neutron beams for research, or neutrons for materials testing or any other purpose. The main applications of this heat are electricity generation and naval propulsion. Some power reactors have also provided building heating, and one Soviet power station was also used for desalination.


Reactors intended for purposes other than producing heat and/or Plutonium production are often designed primarily for research, and called research reactors for that reason, but are often also used for other purposes. They are a general purpose source of neutrons, and generally a lot smaller than either power station or Plutonium production reactors.


So when classified by purpose, there are three main types of reactor:

  • Power reactors
  • Plutonium production reactors
  • Research reactors 

and they are each designed in different ways, to best achieve their purpose. The French UNGG and British Magnox reactors were built as dual-purpose power and Plutonium production reactors, see below, but even these couldn't do both at once.  And the Americans generated a little electricity from at least one of their Plutonium production reactors, for local consumption, and the Soviets are rumoured to have used one of theirs for space heating, but both of these were afterthoughts that didn't affect the basic design.   


PWR stands for Pressurized Water Reactor. This is a power reactor design developed and still used for nuclear propulsion in US warships (first submarines, later also aircraft carriers and cruisers), and adapted for use in civilian nuclear power plants (and a few others). These days normally, PWR means a civilian nuclear power plant reactor rather than a naval reactor, but it depends on the context. Both contexts are encountered below. All PWRs are power reactors of some sort.


BWR stands for Boiling Water Reactor. Nearly all BWRs are civilian power station reactors but there have been a few others, but all BWRs are also power reactors of some sort. They're similar to PWRs in many ways, but the water boils in the reactor core.  There's no separate steam generator. This has both advantages and disadvantages. This term is used below in explaining the term LWR.


LWR stands for Light Water Reactor. This term will be more of a problem, to the point that it is the main reason for this little glossary! It's a far broader reactor class than PWR or BWR, and includes all members of both of those classes, and that is simple. The problem is, unlike BWR and PWR, the term LWR often also includes lots of non-power reactors. It's generally used to mean any light water moderated and/or cooled reactor, and this includes many small research reactors, such as OPAL. But these are nothing like a power reactor.


In the contexts below, LWR means a civilian power station reactor, either a PWR or a BWR, and no others. The reason for this confusing usage is that it's useful to lump civilian power station PWRs and BWRs together, and there's no better term. It's a very useful term because both PWRs and BWRs are still being both operated and built as power stations, and the two use very similar fuel, and produce similar spent fuel, and therefore similar nuclear waste containing similar Plutonium.


And so that's the meaning of LWR you'll see below, and very notably in the quote from Wikipedia which inspired this whole page. So I'll follow their terminology.


The grade of Plutonium is a measure of its isotopic composition (that is, what isotopes are present and in what proportion) and therefore its suitability for weapons purposes; The higher the grade, the more suitable. Reactor-produced Plutonium consists mainly of two isotopes, Pu-239 and Pu-240. Pu-239 is the desirable isotope both for weapons and for reactor fuel, and Pu-240 the least desirable, particularly for weapons. The more Pu-240 in the Plutonium, the more difficult it is to produce a successful explosion, and the more fallout will be produced by whatever does take place.


Plutonium was first produced using an accelerator, not a reactor, and this was almost pure Pu-239. The realisation that a grade this high could not be produced at all in a reactor called the very use of Plutonium by the Manhattan Project in to question for a while, see Thin Man (nuclear bomb) at Wikipedia.


Some other terms, and notably burnup, and of course fuel grade,  are discussed below, or see a nuclear glossary.


The Gospel according to Wikipedia

I love Wikipedia! I spend hours working on it as a volunteer administrator, sometimes on a daily basis when real life allows.


It teaches me so much. And one thing everyone in the 21st century needs to learn is critical reading. In fact, without that skill, Wikipedia is of very little use and possibly even negative value. But fortunately, critical reading is now part of the primary school curriculum, in Australia at least. Have a look at my essays hosted by Wikipedia at  what_use_is_Wikipedia  and if_the_rocket's gonna crash for more on this.


But more to the point, have a look at




and there you'll read 


IFRs and Light water reactors (LWRs) both produce reactor grade plutonium, and even at high burnups remains weapons usable,[27]


which is an interesting and not unusual claim and belief. And a lie. Well, the IFR could be operated to produce weapons usable plutonium, but it doesn't in normal operation, while the LWR can't be, except in fantasy. Overall, the claim is a complete lie.


But it's a commonly believed lie. Why so? What has made this particular lie so easily promoted?


That particular claim could be removed from the article (and by now perhaps someone has, that's why I gave a permalink to a particular version).


The claim made in the Wikipedia article is the result of (typically) poor research, and somewhere along the line, probably dishonest research. I'm sorry but I will pull no punches. As an undergraduate student, I was once laughed off the front lawn of Macquarie University for asking an anti-nuclear speaker whether it was true that, as he was suggesting, Plutonium had a longer half-life than Uranium. He replied angrily that of course it was true, and most of the student body believed him. The science students were of course laughing too, but for a different reason (look it up, or see crossover period and go the the section headed Nonsense).


And that, quite frankly, is typical of the quality of (mis) information provided to and naively repeated by your local greenie.


Another interesting Wikipedia claim is hereAfter World War II, uranium-based nuclear reactors were built to produce electricity. These were similar to the reactor designs that produced material for nuclear weapons. Um, no, the first generation was a mixture of prototype designs, and they included the PWR, which used (and still uses) enriched oxide fuel, water moderator, and high fuel burnup, and it quickly dominated the industry and still does. And it's nothing like a World War II plutonium production reactor, or even a cold war one, which all used unenriched metal fuel, graphite moderator, and minimum fuel burnup. And all of these changes were made for very good reasons, and some (perhaps all) of them are highly significant as we will see below.    


The facts are that nobody has ever made a bomb from spent LWR power station fuel (or IFR fuel, but there's only been one IFR, called EBR2), and there are good reasons that they haven't, and for those same reasons nobody is ever likely to do so. It's far cheaper and easier and faster to make weapons grade material from scratch, and even easier and cheaper to hide the fact that you're doing it. Using spent LWR power station fuel in a bomb program would be a bit like drinking purified sewerage when you lived on a clean, drinkable river. It's possible, but you'd only do it for a dare, or to prove a point.


A fascinating story

Which brings us to the probable source of these lies, and the purpose of this page.


In 1977, President Jimmy Carter (often described as a trained and qualified nuclear engineer, including on previous versions of this page, but he never finished training, see here) released details of two 1962 nuclear tests that used what was in 1962 called reactor grade Plutonium. This was a political move to justify his decision to ban reprocessing of spent nuclear fuel, and wasn't his only peculiar decision on matters nuclear.


As part of the release of this information, the DOE revised their grading system for Plutonium. Up until the announcement, they recognised three grades: 


  • Super weapons grade, less than 3% Pu-240, The highest grade. Expensive and used only for weapons that are stored for long periods in close proximity to working staff, such as in the torpedo room of a submarine. 
  • Weapons grade, less than 7% Pu-240. The stuff that destroyed Nagasaki, was to be used for the funded program to subsequently drop five more bombs every two months on Japan, and has been used in nearly all bombs since then.
  • Reactor grade, 7% or more Pu-240. The lowest grade. 


In 1977, and to this day, they added a fourth grade (or if you like, a second and lower intermediate grade), fuel grade, 7% to 19% Pu-240.  So the grade previously known as reactor grade was split in two, and between weapons grade and what is now known as reactor grade there's a fourth grade, especially created for this announcement. And the material that was used in the 1962 tests is somewhere within the range of this new grade. In 1962 this material was called reactor grade, but since 1977 it has been called fuel grade. What is now known as reactor grade is a lower grade than fuel grade, and this reactor grade is not the stuff that they made go bang in 1962.


So the grades now are:


  • Super weapons grade, less than 3% Pu-240, The highest grade, very useful for special bombs.
  • Weapons grade, less than 7% Pu-240. An intermediate grade, but still useful for bombs and the normal stuff for them.
  • Fuel grade, 7% to 19% Pu-240. An intermediate grade, made to go bang in 1962, and produced specifically for those tests.
  • Reactor grade, More then 19% Pu-240. The lowest grade, and the stuff produced in normal operation of LWR power stations. Never used in a bomb, or likely to be.


It would be fascinating to know who actually invented this new grade, and decided to reuse the name reactor grade for what was now the poorer of the two new grades. The smart money is on Carter himself, but we'll never prove it.  The creation of this new grade added some very useful and important detail to the information that was released, but it also had another rather more subtle consequence.


The tests were successful. But what was not at all obvious from the 1977 press releases and subsequent discussion was that they didn't use the spent power station fuel that Carter didn't want reprocessed, or even Plutonium of a similar grade.


In 1962 in fact, there wasn't very much if any such spent power station fuel available for them to use, Shippingport, the first American PWR power station, went critical in 1957 and had been partly refueled only three times by 1965 when the whole fuel load was changed, but in any case this was a highly enriched uranium fuel, manufactured for use in naval PWR propulsion reactors and quite unlike that used in later PWR power stations, which created the waste that Carter didn't want reprocessed.


And even if the material had been available they would probably not have used it. The plutonium actually used had been produced in a power station, yes, but not in an American one or even one of similar design. To do that might have been possible, but ridiculously expensive (see below) and also, in the case of American plants, illegal. So instead, they used a far cheaper and perfectly legal source.


So interesting fact one: While the Plutonium used was at the time of the 1962 tests called "reactor grade", it was a lot richer in Pu-239 and poorer in Pu-240 than the spent fuel that Carter wanted to justify not reprocessing in 1977, which was called "reactor grade" in 1977. That's the significance of the invention of "fuel grade" for the 1977 announcement. 


The stuff that Carter didn't want reprocessed was called reactor grade in 1977. The stuff that went bang was called reactor grade in 1962. The 1977 announcement sort of implied that they were the same stuff, but they weren't, and the announcement didn't actually say they were, it even then explicitly said that they weren't.


Interesting fact two: The Plutonium was supplied by the British, and produced in their Magnox power reactors. These plants were specifically designed to be able to produce weapons grade Plutonium. They were dual-purpose, so producing this intermediate grade in such a plant was relatively cheap and easy.


So these 1962 tests tell us nothing about whether reactor grade plutonium, and even at high burnups remains weapons usable (to quote Wikipedia as the article stands in 2018), any more then the paper on controlling weapons grade material that was cited there as justifying this (rather common) claim does. In the terminology invented for the 1977 announcement, it wasn't reactor grade Plutonium that was used. It was fuel grade, a higher grade than (1977) reactor grade, and the 1977 announcements said this quite explicitly.  


But in 1962, it was called reactor grade, so the declassified documents of the time refer to it as this. Isn't it clever? The DOE told no lies, except by omission. Anyone now reading the original documents now naturally assumes that the Plutonium used was more than 19% Pu-240, when if fact we have known since 1977 that it was a higher grade than that, and perhaps as little as 7% Pu-240. The exact composition wasn't released, for obvious reasons, and hopefully never will be, any more than the rest of the test data has been or should be. These were successful tests. Let us keep the details secret from those who don't know them and would very much like to use them to help build their own nuclear bombs.


The point of course is just that the grade of Plutonium used in the 1962 tests was higher then anything ever produced in any of the LWRs then and still in use in the USA, or in any similar reactor, anywhere in the world. And Carter knew this.


If that wasn't bad enough, in every practical sense it can't be produced in these reactors, and anybody who knows their stuff will tell you that if they're honest.


Well, perhaps nothing is impossible. But let's just see what would be necessary to do it.


Burnup, refueling, and LWRs

The key word here is burnup. Burnup is measured in megawatt days per ton, or more properly megawatt days per ton of heavy metal, and is a rough but useful measure of how much neutron irradiation the fuel has received. This could be for a long time at a low power level (which means that there are relatively few neutrons around), or for a short time at a higher level, but either way it's a good indication of the isotopic composition of the irradiated fuel. And it's this isotopic composition, and particularly the amount of two isotopes of Plutonium, that determines the grade of the Plutonium that is produced. 


And of course it's the grade of the Plutonium that determines how useful it is in making a bomb. The lower the grade, the more difficult it is to produce an explosion rather than a fizzle.


And making even high grade Plutonium explode is a far more difficult and complex and expensive exercise than producing it in the first place. Inefficient Uranium-235 bombs are dead easy to make once you have the weapons grade material known as Highly Enriched Uranium or HEU. The one dropped on Hiroshima was the first ever made, the Manhattan Project thought there was no need to test it and they were proved correct. Plutonium is a different story entirely. The Manhattan Project was so keen to test the implosion tehnology required, they used a billion dollars (and that's 1945 dollars) worth of Plutonium to do so. It worked first time, but North Korea has now produced high grade Plutonium, and it's not clear whether they've yet made it go bang, but we do know they had several fizzles trying, before successfully exploding several bombs which may have relied on HEU. The South Africa/Israel bomb used HEU, like the Hiroshima bomb. They presumably considered the Plutonium route but rejected it as far too hard. 


Low burnup is essential in order to minimise the amount of Pu-240 (and Pu-241 and Pu-242, but Pu-240 is the important one) in the irradiated fuel. Because, Pu-240 is produced by irradiating Pu-239. This doesn't happen very much, obviously, early on in the irradiation of the fuel, simply because there's not a lot of Plutonium there to irradiate. So the trick is, get the plute out of the reactor as soon as possible after it is created. Which means, at low burnup.


And it's not practical to separate the Pu-239 from the Pu-240. In theory it's possible, but nobody has ever done it or expects that anyone ever will. It's far, far more difficult than separating U-235 from U-238, because of the closer mass numbers, and just separating those two Uranium isotopes (called Uranium enrichment because the goal is to increase the percentage of fissile U-235) requires enormous and expensive plants (which is one reason that nearly all bombs since Hiroshima have used Plutonium instead). So it's far cheaper and quicker and easier just to produce high grade plute in the first place. But that means low burnup, and that means frequent refueling.


How to wreck a reactor

In the Magnox, refueling can be accomplished simply by positioning a refueling machine over the channel containing the fuel element you want to change, and removing and replacing the fuel. It was even planned to do this without shutting the reactor down, as was done with the original British Plutonium production reactors at WIndscale, but in practice this wasn't generally done. This frequent refueling is essential to produce low-burnup fuel, and the reactor was designed that way for that reason.


To produce even fuel grade plute in an LWR, you'd similarly need to refuel it every couple of days. But in an LWR, this means cooling and depressurising the whole system, and (partly at the same time) disconnecting all the control rods, the instrumentation, everything that goes through the top of the pressure vessel (known as the "head"), which in a PWR is everything except the plumbing. (In current BWR designs the control rods go through the bottom of the reactor vessel, but there are other complications as a result.) Then, unbolting and removing the reactor head (many tons of steel, it's the whole top of the reactor pressure vessel) and flooding the reactor building with borated water, changing the fuel, and then reversing the process to put it all back together. It normally takes weeks or months, and that's reasonable if you're only doing it every few years. But you might get it down to under a fortnight by cutting corners. Then you go to power for a couple of days, and then repeat the process.


See https://www.quora.com/How-is-a-nuclear-reactor-defueled for three accounts from people who have actually refuelled such a reactor, and/or the diagram below for some idea of what this involves.



Oh, and that's assuming you don't run into any extra problems. The guys who designed the wiring and mechanical connections did so to a budget. They expected them to be disconnected every few years, and that on these occasions there would be plenty of time to inspect them and replace anything that was worn or broken in the process, so they took this into account. That was their job. But now you're doing it fortnightly, and in haste. Things will wear out and break. Worn and even broken bits will be reassembled without adequate checking, and result in further delays. Just a few jammed control rods or one jammed fuel element will probably write off the reactor, or at least shut it down for a year or so while expensive repairs are devised.


Or if any of the seals in the reactor head leak when you go back to pressure, you have to decide whether to take another fortnight to pull it all apart again and fix the leak, or run with the leak. The reactor vessel operates at about 153 atmospheres, which is 2,250 psi, so those seals are both rugged and delicate. Running with the leak has only ever been tried once as far as we know, by an American PWR. The corrosive borated water ate a hole in the reactor head and the reactor was a writeoff. Good luck!


So the production of even fuel grade plute in an LWR would take years, probably decades, during which time it produces no significant electric power (and neither does a Magnox or the French equivalent the UNGG when used for Plutonium production, by the way), and after which the reactor would be a wreck. And it would all be noticed by the international community of course!


And that's just the start of your problems, but it's more than enough. Solve them and perhaps then we can discuss exactly how you're getting (and financing) all this fresh, enriched Uranium oxide fuel to cut up and reprocess at low burnup. Or if you've got your own enrichment and fuel fabrication plant, why aren't you going the HEU route? Far simpler. 


In summary, the whole idea is ridiculous.


But aren't there already a few low burnup elements?

Ah yes, fuel that is removed prematurely, because of fuel cladding failures, or other unplanned events? Yes, there have been isolated incidents of this, and each of these fuel elements contains a little high-grade plutonium. They are currently in dry cask storage, along with hundreds of highly radioactive, high burnup fuel elements, each containing much more plutonium, and of a much lower grade. And that's a reasonably safe place for them. Nobody can easily access or even identify them... I mean, identifying one of them is dead easy with a geiger counter, once you have it on its own away from all those other highly radioactive high burnup elements, but that's not a trivial exercise to say the least. It would be much better to reprocess all of this spent fuel of course, which would dilute this little bit of high grade plute, but Carter decided not to do this.  


And in theory, if we patiently collected all of these low-burnup elements together and nobody stopped us, in a few thousand years' time we'd have enough weapons grade material for one bomb, and could then build a special plant to reprocess this spent fuel to recover this weapons grade plute. This low-burnup fuel is not itself highly radioactive (that's how we identify it), but it is oxide rather than metal, and it must not be mixed with even traces of other spent fuel obviously, as this will dilute the precious high-grade plute. See above and below for more on why these matter. Ummm, another reality check?  


How not to wreck a reactor

So the other way is, use high-burnup fuel to make a weapon, as the Wikipedia article clearly suggests. Honest spent fuel, produced in normal operations, containing honest reactor grade Plutonium, which nobody has yet made go bang (or even been silly enough to try to). But even if you think you can be the first to do so, there is still the little matter of reprocessing. Getting the plute out of the spent fuel.


Low burnup fuel is relatively benign. At Windscale, the fuel channels were horizontal. Staff pushed new fuel slugs into these channels using broom handles, and the irradiated fuel simply fell out of the channels into tubs of water on the other side of the reactor. On at least one occasion, a slug missed the tub, so one of the staff walked into the "hot" area, picked up the fuel slug with his bare hands, dropped it into the tub, and got the hell out of there. He suffered no ill effects.


Try that with a fresh spent LWR fuel element and your life expectancy is measured in milliseconds, because of the intense and highly penetrating gamma radiation from the large amount of fission products the fuel now contains. Low burnup fuel contains far fewer fission products, and Pu-239 is an alpha emitter, and its radiation bounces off a thin sheet of plastic, or off your skin. So you can safely reprocess fresh low burnup fuel to extract the Plutonium in a perspex glovebox, an inexpensive and  common facility found in many (perhaps all) laboratories that process radioisotopes, worldwide. That's how the Manhattan Project did it, and so has everyone since so far as we know. Reprocessing spent LWR fuel, on the other hand, takes place behind several feet of high-density concrete using expensive remote handling, in large expensive hard to hide plants called "canyons".


(And these "canyons" are also necessary for processing high-burnup Magnox fuel of course, which is most of it. If the aim of the exercise is to produce electricity at a competitive cost, you go for the highest possible burnup, which is exactly what an LWR is designed to do. With a Magnox, you have a choice. With an LWR, in practice you have no choice whatsoever. The design just doesn't offer that option, and Carter knew this too. The reactors on which he started training were naval PWRs.)


And it's a relatively minor matter, but we might also consider that reprocessing oxide fuel (as used in all LWR power plants to date) is a lot more difficult and expensive than reprocessing metallic fuel (as used in all Plutonium production reactors to date, Magnox included). This is far more of a problem with high-burnup fuel, when you're doing it all by remote control.   


Jimmy was right to be nervous about reprocessing (but probably wrong to ban it rather than control it and use it to support the NPT, but that's another story). It's mainly just a shame that he decided to lie to get support for his decision. White lies, perhaps. Clever lies of omission. But still lies, and ones that diverted discussion from the real issues, and continue to do so.


Anything is possible, but...

It's theoretically possible to make a bomb using the Plutonium from low burnup irradiated LWR fuel, sacrificing the electricity production and using lots of fresh oxide fuel elements and building a dedicated reprocessing plant to do it. But it's fantasy, and has never even been attempted so far as we know. It's far, far cheaper and faster and easier to build a Plutonium production reactor, like a small Magnox (or a UNGG), and a reprocessing facility for the low burnup metal fuel. Which is what everyone who has made or attempted to make a Plutonium bomb has done (well, India initially used a small research reactor, but the point is, it was not a power station). Most recently of course North Korea (using the drawings and specifications of the Magnox irresponsibly declassified by the British).


And if you got this far (and thank you) I hope you now understand why this is so. Plutonium from LWR fuel is weapons usable (again to quote Wikipedia) in fiction only.


(I will add one qualification. There's one way to enrich Plutonium. Bury it and wait. Pu-239 has a much longer half-life than Pu-240. Is anyone likely in the far distant future to dig up Yucca Mountain? Or possibly also some decaying dry casks - no. surely eventually the penny will drop that the choice isn't between reprocessing and nothing but between reprocessing and something else, for this existing spent fuel at least, and that the US military have now given up and quietly built their own facility instead. Anyway, point is, will they mine this super weapons grade plute?


They will of it's there. Hopefully, they will use it as reactor fuel. But for the IFR, the low-grade Plutonium and Uranium that Carter seems to have decided to bury is already perfectly good fuel. So why not burn it now, along with all of the other transuranics, and some of the fission products?)


And I hope you also now understand why the claim that it's practical to make the plute from irradiated LWR fuel go bang, and that the 1962 tests proved that it is, is quite simply a lie, and always has been.


And why the fact that this lie is still so widely believed and repeated is so very, very sad.


See also


And if you're really brave 

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