Why You Cannot Build a Nuclear (Fission) Reactor At home

June 16th, 2013
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What a nuclear reactor is:

In order to continue, it is important to first qualify exactly what a nuclear reactor is.  In some sense, one could consider any device in which a nuclear reaction occurs to be a reactor, regardless of the type of reaction.   By this definition, combining an alpha emitting isotope with aluminum or beryllium would be a nuclear reactor, since some of the particles will be absorbed and produce a simple nuclear reaction.

Within most context, however, the term “nuclear reactor” is understood to mean a fission reactor.  That is, a device which produces a sustained fission chain reaction using a material like uranium or plutonium.  This normally means that the reactor must achieve critical mass.  However, fission can also be achieved in a sub-critical mass by producing neutrons from an external source such as an accelerator in what is known as a subcritical reactor.

Nuclear fusion reactors are completely distinct from nuclear fission reactors.  Although a nuclear fusion reactor could be called a “nuclear reactor,” doing so, without qualification, is likely to cause confusion.  Nuclear fusion reactors come in a variety of types and it is possible for advanced amateurs to build simple electrostatic fusion reactors, such as the Farnsworth Fusor using commercially available materials.   While these fusors are indeed true fusion reactors, in that they can produce nuclear fusion, the amount of fusion they produce is very small and the neutron radiation generated is low enough to make them relatively safe to operate.   They do not require any radioactive materials for construction or operation.

Once in a while you will see a story in the news about an amateur building a “nuclear reactor” for a science fair or demonstration.   This generally means that they have constructed a fusion reactor, usually in the form of a Farnsworth Fusor.  While doing so is certainly an accomplishment and a very advanced amateur science project, it is not a “nuclear reactor” in the sense of a fission reactor.   It produces no usable energy and only limited neutron flux.

Building a fission reactor is something else entirely.

Why this is just a bad idea:

First of all, if you were to build a nuclear reactor at home, you could very easily kill yourself from radiation poisoning.  Real nuclear reactors require a substantial amount of shielding, usually in the form of water and a material like concrete.   Without enough shielding, exposure to the core neutrons could be fatal, even from a relatively small reactor.  Unshielded nuclear reactions have occurred during criticality accidents, and have caused serious injury or death.   Any reactor that produces more than about a watt of power should be, at the very least, operated at the bottom of a pool of water.   Thankfully, no amateur is likely to get this far.

Many of the other materials used in attempts to build amateur nuclear reactors are quite dangerous.

Uranium is toxic, though only mildly so.   However, extracting uranium from ores or other materials requires a strong acid or base solution, which can be dangerous to handle outside of properly controlled settings.  Am-241, the isotope found in smoke detectors, is highly radioactive.  It is extremely safe, as long as it is kept in the form of a ceramic embedded in gold foil, but if it is extracted, even small amounts can be very hazardous if inhaled.

Some amateurs have used radium-226 in their reactor experiments.  It’s a powerful alpha emitter which can be obtained with relative ease from the luminous paints found on old clocks, aircraft instruments and gauges.   Radium-226 is extremely radio-toxic and is easily absorbed.  It is rapidly incorporated into bones and teeth.  The radium salts found in radium paint also have a nasty tendency to stick to surfaces, making decontamination difficult.  Flaking radium paint can produce dust that is easily inhaled.   Hence, working with radium is dangerous and should be avoided by amateurs.

One of the reasons radium is desired is that it is a high energy alpha emitter, which can be used to produce neutrons when combined with beryllium.  Beryllium is yet another dangerous material that should not be handled by those who lack the proper experience and equipment.  Beryllium is highly toxic, especially when inhaled.  Beryllium dust is easily kicked up into the air and inhaling even small amounts can be extremely harmful.

Examples of those who have tried to make homemade reactors:

David Hahn David Hahn gained fame as “The Radioactive Boyscout” when in 1994 he attempted to build a nuclear reactor in his parents tool shed. Hahn was only 17 at the time and managed to build an impressive amount of material, given that he built his device before sites like eBay were widely available.

Hahn’s materials included antique clocks, smoke detectors, lantern mantels, uranium mineral samples and small amounts of uranium, which he obtained from a chemical supplier.  In order to extract and purify the materials, Hahn also used lithium, derived from lithium batteries, household bleach, saltpeter and other common chemicals.   Hahn managed to conduct some pretty complex and advanced chemical reactions including the synthesis of nitric acid, which he used to extract and concentrate uranium.

He was almost entirely self-taught, relying on library books on chemistry and nuclear energy along with advice he received from the NRC and other government agencies.  Hahn posed as a professor and wrote letters asking for advice on how to conduct small-scale classroom demonstration experiments.

Hahn’s “reactor” was basically a neutron source which he created by collecting radium from antique clocks and americium from smoke detectors, which he combined with aluminum. The neutrons were produced when high energy alpha particles struck the aluminum creating a tiny number of fusion reactions  He started off with a simple “neutron gun” consisting of the alpha emitting material in a lead block with a piece of aluminum foil on one end.  He later upgraded his neutron source by securing a strip of beryllium, a more potent producer of neutrons than aluminum.

Using this simple neutron source, Hahn was able to irradiate materials with enough neutrons to produce a detectable increase in radioactivity.   By focusing his neutron source on thorium, which he had extracted from lantern mantles, he was able to create a tiny amount of uranium-233.   Based on the success of his initial experiments, Hahn hoped to create enough uranium-233 to produce a true nuclear reactor.

The next step was to convert the neutron gun into a kind of “core” by combining the alpha emitting material and beryllium and surrounding the neutron source with moderating material, which he constructed out of tritium-based paint, amongst other material. (whether or not this worked better than a cheaper moderator seems suspect.) He used this neutron source to irradiate thorium, which he had extracted from lantern mantels and uranium, which he had ordered from a chemical supply company. His hope was that the neutron radiation would convert the thorium into fissionable uranium-233 and the uranium into plutonium.

The device did indeed produce some uranium-233 and plutonium, but only in microscopic quantities. It could be described as a “breeder reactor” in this sense, as it did breed some fuel, albeit far too little to be a viable fuel source. It was not a true reactor in the conventional sense, however, because it never achieved a fission chain reaction or even came close.   That said, he had managed to concentrate enough radioactive material to be detected some distance away and, based on some reports, the neutron flux may have been high enough to increase the total radioactivity of the material through neutron activation, and therefore, would presumably have been producing a steady stream of U-233 and Pu-239, although in tiny quantities.   This is a pretty impressive achievement for a 17 year old.

Still, he managed to create quite a mess with his experiments. After being questioned by police for the routine complaint of “loitering” the material was discovered in his car, leading to an investigation, ultimately resulting in his shed being torn down and declared low level radioactive waste. Whether this was necessary might be debated, but clearly his activities were not safe from either a radiological or chemical standpoint.   All things considered, it’s pretty amazing that the authorities did not overreact and evacuate the whole town, but this was in 1994, before paranoia had reached its current levels.

Hahn’s device, which I hesitate to call a reactor, was truly a testament to backyard ingenuity and an accomplishment for someone of his limited means.  Still, it was not the safest thing to do, from an industrial hygiene perspective and certainly is not recommended.

Richard Handl – If David Hahn’s experiments seem a bit dangerous, Richard Handl’s are just plain stupid.  Mr. Handle, of Sweden, seems to have come up with the idea of building a nuclear reactor in the kitchen of his small apartment. Like David Hahn, Richard Handl tried to build his reactor using a small amount of uranium as well as americium (from smoke detectors) combined with radium and beryllium, creating a makeshift neutron source.

You can read about his experience on his blog “Richard’s Reactor.“   He was apparently doing this entirely in public (at least on his blog) but didn’t seem to get the attention of any authorities, until he eventually decided to ask the Swedish government whether what he was doing was legal.  The result was a visit from the police and the confiscation of his materials.  He was charged with illegal possession of hazardous chemicals, impersonation of another person and violation of radiation safety law.   At least word, the first two charges were dismissed. It’s unlikely he’ll end up in prison, but his actions were still amazingly stupid.

The materials Mr. Handl acquired are safe on their own, but he certainly did not handle them safely.   Americium is perfectly safe, as long as it remains in the stable form of a smoke detector tablet.  Radium-226 is generally safe in the form of antique luminescent paint, as long as the paint remains relatively intact is not scraped or dissolved from things like clock faces.  Beryllium is a toxic metal – relatively safe as long as it remains in a solid mass, but should never be ground, machined or otherwise worked without proper precautions.

The image to the right shows what happened when Richard Handl tried to cook the materials on his kitchen stove! Note the large number of cigaret butts, a bottled soft drink and what appear to be candies or gift boxes – this was not a sterile and controlled laboratory!

Here is what he had to say about the spill:

A meltdown on my cooker!!!
No, it not so dangerous. But I tried to cook Americium, Radium and Beryllium in 96% sulphuric-acid, to easier get them blended. But the whole thing exploded upp in the air…

Of cource I thrown away my pills at the left side, and I didn’t drink the juice-syryp in the right.

WHAT? NOT DANGEROUS? Sorry, but I do not think that not drinking the juice-syrup and not taking the pills qualifies as being judiciously cautious. Radium, beryllium and uranium should be absolutely nowhere near a food preparation area. The microscopic amount of radium in paints may not be dangerous externally, but can be extremely harmful if ingested.

I’m not even sure what substance listed I’d consider the most idiotic to cook on your stove – probably 96% sulfuric acid!

But, even if you happen to do things a lot smarter and in a much more controlled manner than Richard Handl or David Hahn, building a fission reactor is a losing proposition.  The biggest problem is the fuel required and the quantity you would need.

Potential Fuels:

Plutonium - Unobtainable to anyone outside of a government agency or a large industrial company.   Plutonium must be produced artificially and then separated from uranium chemically.  It is both very well secured and very expensive.  The only way an ordinary person might be able to obtain a quantity of plutonium would be by tracking down a sample of material that was somehow contaminated with plutonium.   For example, trinitite, a glass produced by the first nuclear weapons test contains microscopic amounts of plutonium.

Such samples contain microscopic levels of plutonium.  Any material which contained more than traces was always sequestered and removed from the site.  Today, these samples are primarily of interest to element collectors, since it is the only legitimate source of plutonium.  The quantity would be far too low for consideration for a nuclear reactor.

Americium-241 -This is the most familiar of all artificially-produced elements as it is the only one available in consumer products.  Ionization smoke detectors use a small amount of Am-241.  Certain industrial equipment may use larger amounts.   Americium-241 is fissile, with the critical mass for a bare sphere of the material being about 60 kg. If Am-241 were used to fuel a reactor where it would be placed in an efficient moderator, substantially less would be needed, possibly as little as a few kilograms.

Such quantities would be impossible to accumulate from sources like smoke detectors, which only contain a fraction of a microgram per unit. In fact, it would take more than a billion smoke detectors to acquire enough Am-241 to create a nuclear chain reaction. The amount that could be recovered from a more practical number of smoke detectors (perhaps several thousand) would be nowhere near enough to create a reactor.

Highly Enriched Uranium – Highly enriched uranium, like that used in nuclear weapons, military reactors and some research reactors would allow for creation of a small nuclear reactor with relative easy.  However, it is extremely expensive and very closely guarded.  There is no way that HEU could be obtained by the average person and certainly would not be legal to purchase or own.

Low Enriched Uranium – Low enriched uranium has concentrations of U-235 up to a few percent and is used in most commercial nuclear power reactors.  It is certainly not something the average person could ever purchase.   Although it is not guarded with anywhere near the kind of security that plutonium or HEU is, it is still not something that would ever be legally obtainable in any quantity.

There are some accounts that have circulated about LEU uranium pellets being available outside of the normal supply channels for reactor fuel.  For example, pellets which do not meet quality control standards might be available to employees of fabrication facilities.   Such stories are hard to confirm and the legality of private ownership of LEU is difficult to determine.  However, even if a person could acquire several LEU pellets, this would not help get them very close to building a nuclear reactor.

Even highly efficient moderators, neutron reflectors and other measures were implemented, one would need a minimum of several tons of LEU to achieve critical mass.  Such quantities are not obtainable to any individual.

Uranium-233 – Uranium-233 is the fuel used for thorium cycle reactors.  It is produced from the neutron irradiation of thorium.  Limited stockpiles of U-233 exist and are impossible to obtain of in any quantity, as it is generally regarded as being potentially weapons material.

Thorium is obtainable, and it is possible to generate neutron radiation by combining available alpha radiation emitters and beryllium or even by building a very small fusion reactor.  This seems to be what David Hahn was attempting to do with his small neutron source and thorium.  However, one would never be able to produce enough U-233 for a reactor or even anything close to it.  The neutron flux that is obtainable from a homemade source is trivial and thus would produce only miniscule quantities of U-233.  Even milligram levels of production would be out of the question without a nuclear reactor as a neutron source, and critical mass would require a minimum of more than a thousand kilograms.

Natural Uranium – This is the ONLY material that the average person would have any chance of acquiring and which could be used to build a nuclear reactor.  Uranium can be purchased as a metal or a compound, but very few suppliers exist, and, because it is such a specialty product, it tends to be expensive.  Most uranium used in laboratory chemicals and consumer products is depleted uranium, which would not be usable as reactor fuel on its own.

The most straightforward way of obtaining large quantities of natural uranium would be to extract it oneself from uranium ore.   Uranium ore is readily obtainable and rock containing high concentrations of uranium can be found in locations around the world.  The process of extracting uranium is not terribly complicated and can be demonstrated using readily obtainable materials.   First, the uranium ore is crushed and pulverized then the resulting material is placed in an acid solution.   Even the hydrochloric acid solutions available from hardware stores are sufficiently acidic for this purpose.   Nitric acid will work even better and is obtainable from any chemical supplier.  The acid solution will dissolve the uranium out of the rock while leaving behind the bulk of the rock material, which can be screened out.

There are a few ways of removing the uranium from the acid solution.   The simplest is to just add a base to neutralize the solution, which will cause the uranium to precipitate out.  The result is a mixture of uranium salts.   This material can be further processed by other methods to obtain uranium oxide.   Converting it into uranium metal is more difficult but not impossible.  For use in a reactor, the uranium must be of a very high purity, so regardless of which technique is used, there will have to be a final solvent-solvent extraction step to remove any contaminants from the uranium and produce material pure enough to be used in a nuclear reactor.

The acid extraction method works well with many common ores such as uranite, but will not work with carnotite or other uranium ores that are too alkaline for this method.  An alternative method is to use an alkaline extraction method or various types of solvent extraction.

Basic information on how to preform uranium extraction demonstrations can be found from United Nuclear’s website.   Preparing uranium compounds of relatively high purity is certainly not beyond the capabilities of any advanced amateur with access to uranium ore and the desire to do so.   However, what makes this an unrealistic source of reactor fuel is the sheer amount of uranium that would be required.   Using a small ballmill and laboratory flasks would never be sufficient to produce enough fuel for a reactor.  In fact, doing so would require nothing less than an industrial-scale operation.

How much uranium will be required:

How much natural uranium will be required depends on the moderator being used in the reactor and the design of the reactor.  If natural uranium is the fuel, only the most efficient moderators, with the lowest neutron capture cross-sections will work.   Regular water or “light water” is the most common moderator in nuclear power reactors, but it will not work at all in a reactor fueled by natural uranium.  Only enriched uranium, and many tons of it, can be used with light water.  Natural uranium will require a much more efficient neutron moderator.

The simplest, most easily available and low cost moderator suitable for a natural uranium fueled reactor is graphite.   Not all graphite will work for this purpose.  A good example of a “small” graphite-moderate natural uranium reactor is Chicago Pile-1, which is also the first nuclear reactor ever successfully demonstrated.  CP-1 was designed by Enrico Fermi using calculations from smaller subcritical experiments.   It was intended to be only barely large enough to achieve a sustained chain reaction.   In fact, the reaction was so small that no radiation shield was needed and very little heat was generated.   The only way of even knowing that the reaction was occurring was by the readings on instruments measuring the radiation produced by the reactor.

CP-1 used about forty short tons of natural uranium, in the form of uranium oxide and uranium metal.  It also contained four hundred short tons of graphite, milled into 45,000 blocks. It’s possible that the size could be reduced slightly by making some design changes, such as distributing the uranium in smaller fuel elements, and thus increasing the moderation effect of the graphite, but not by very much.  CP-1 is approximately as small as a graphite-moderated, natural uranium reactor can get.  Still, it weighed hundreds of tons and required a great deal of labor to construct.   The high purity graphite blocks had to be machined to fit perfectly together and construction was laborious.

It is possible to reduce the amount of natural uranium required by using an even more efficient moderator than graphite.   Deuterium oxide, also known as heavy water, is another option for moderating a natural uranium fueled reactor.   It is even more efficient than graphite and therefore requires less uranium to achieve critical mass.  Heavy water is chemically identical to light water, but it has been isotropically separated and contains mostly deuterium, an isotope of hydrogen that occurs in only trace amounts in natural water.  Because of energy and effort required to separate the isotopes, it is very expensive.

According to information from the Oak Ridge National Laboratory, it is theoretically possible to build a natural uranium-fueled reactor, moderated by heavy water and containing as little as about three and a half metric tons of uranium oxide.  However, such a reactor would require a very large amount of heavy water to act as both the coolant and as a neutron reflector.  In total, well over 20 metric tons of heavy water would be required.  It is possible to use less heavy water in a reactor, if larger amounts of natural uranium are used.  For example, CP-3, the first heavy water reactor, used substantially less heavy water but required substantially more natural uranium.  CP-3 only used 6.5 short tons of heavy water – about 7 metric tonnes.

While 3.5 tonnes of natural uranium might seem more reasonable than 40+ tonnes, it’s still a lot of uranium to acquire.  The bigger problem will be the cost of the heavy water.  Heavy water can be purchased from most major chemical suppliers, as it is used as an isotopic tracer and for certain spectrographic applications.   The cost ranges from 300 to 600 US dollars per kilogram wholesale, but is likely to be more if purchased retail by an end user.   Therefore, the heavy water in a reactor would be millions of dollars by itself.   That is not even to mention the cost of the precision, high purity cladding required, the uranium or the construction of the reactor vessel.    Not only is cost a problem, but buying thousands of kilograms of heavy water would put a run on supplies of the material, as it is only used for special applications and rarely would be purchased in such large quantities, except for nuclear reactor use.

Slightly better efficiency and thus smaller fuel requirements could likely be reached through the use of an aqueous homogenous reactor, although this would still require milli0ns of dollars of heavy water and tons of uranium.  Furthermore, the nature of aqueous homogenous reactors necessitates special materials be used to resist corrosion, complicating construction further.

To Sum Up The Fuel Problem:

Plutonium - Unavailable
Highly Enriched Uranium – Unavailable
Low Enrichment Uranium – Difficult to Impossible to get.  Perhaps small samples could be obtained, but nowhere near what is needed
Uranium-233/Thorium Cycle – Unavailable and too high a neutron flux is required to breed it on ones own
Americium-241 – Available, but only in microscopic quantities
Natural Uranium – Available in small quantities.   Large quantities would require refining of ore, which is a major undertaking on a large scale.

Reducing the size necessary:

Unfortunately for would-be reactor builders, there is very little you can do to reduce the size necessary to achieve critical mass.  Using a large neutron reflector, composed of high purity graphite, beryllium or heavy water can help, but only slightly.   Adding a more potent fission fuel, such as Am-241 could also reduce critical mass.  However, since only microgram quantities can be obtained, it would have an insignificant impact.

One approach that was used by both David Hann and Richard Handl was to generate supplemental neutrons in order lower the critical mass needed to keep the reaction going by reducing the need for fission-derived neutrons. The way both tried to do this is by using a homemade mixture of beryllium and radium-226. When beryllium is bombarded by alpha particles, it will occasionally absorb an alpha particle and undergo fusion, releasing neutrons in the process. It seems both chose radium-226 as their alpha source because it’s readily available in the form of antique luminescent paint.  (Technically, one could argue that the use of beryllium-derived neutrons makes it a “subcritical reactor”)

The problem with this approach is that it just does not produce enough neutrons to make a difference in a nuclear reactor.   For every million alpha particles that strike beryllium, only thirty neutrons will be produced.  Homemade neutron sources can be produced by combining americium or radium with beryllium (NOTE: This is not recommended or condoned) but the neutron flux will be extremely low.  It will have no significant effect on the amount of uranium required for a reactor to actually function.

Conclusion:

Those who have tried to build fission reactors in their homes generally seem oblivious to what is actually required and commonly engage in extremely unsafe activities.  The reality is that a nuclear fission reactor requires either materials that are entirely unavailable to the individual or many tons of expensive natural uranium and high quality graphite or heavy water.  The size is irreducible because critical mass must be achieved.


This entry was posted on Sunday, June 16th, 2013 at 9:15 pm and is filed under Bad Science, Misc, Not Even Wrong, Nuclear. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
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81 Responses to “Why You Cannot Build a Nuclear (Fission) Reactor At home”

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  1. 51
    Anon Says:

            BMS said:

    You obviously don’t work for the commercial nuclear industry in the US.

    True, I also don’t design Mars probes for Lockheed Martin.

    :–)


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  2. 52
    ostlandr Says:

    LOL yeah I did it again. Learned to think in foot-pounds and pounds per square inch. Need to reprogram this obsolete brain to think in newtons and pascals. At least the watt and ampere don’t change.

    Anyway, yeah, the weight of the lead coolant/shielding is a problem- we’re talking roughly 3,000 pounds- err, 1,360 kg for a 51 cm diameter x 61 cm long cylinder. That’s roughly equivalent to the dry weight of a heavy truck engine. Add a 225 kg neutron generator, and you’re at 1,600 kg or so. But then for the truck you have to add the weight of the transmission and fuel tank(s). For a Volvo FH with the 16 liter engine, autoshift transmission and max fuel capacity that would total 2,125 kg.


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  3. 53
    Chelsey Jung Says:

    Many thanks for the excellent post, I was hunting for information such as this, visiting have a look at the other posts.


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  4. 54
    John Huston Says:

    What could be built to use as a neutron gun (if your goal is to simply irradiate things) would be a linear accelerator. Unless you can get your hands on a very large quantity of radium and beryllium, this would be the way to go.


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  5. 55
    Anton Says:

            John Huston said:

    What could be built to use as a neutron gun (if your goal is to simply irradiate things) would be a linear accelerator. Unless you can get your hands on a very large quantity of radium and beryllium, this would be the way to go.

    For a neutron gun, you’re going to need a neutron source and a sufficiently powerful electromagnet solenoid(a cylindrical electromagnet where the magnetic flux is highest inside the cylinder). Neutrons have a very weak magnetic moment and the majority of neutron sources, including Farnsworth fusors, emit isotropic neutrons that aren’t particularly useful. The neutron emitting nuclei need to be constrained by a magnetic field to orient their spin axes in the same direction.

    Now it turns out that if you have a Geiger counter, there are places where you can prospect for Uranium ore and then do some chemistry to extract the Uranium. But then you have the problem of isotope separation which requires electrical power much larger than you can obtain from a household power grid.


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  6. 56
    Brayton Says:

    Hello ! Your article is extremely interesting, but I wonder if you are right about using several tons of natural uranium in order to achieve critical mass.Indeed, I live near the EPFL in Switzerland, and they got a research reactor called CROCUS, which only contains about two hundred kilograms of very low enrichment uranium (1.8% and 0.9%) and is moderated by light water.
    Wouldn’t it be possible to reproduce such a setup with a slightly bigger mass of natural uranium, at least less than a ton of it, and still have a critical reactor ?


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  7. 57
    DV82XL Says:

            Brayton said:

    Wouldn’t it be possible to reproduce such a setup with a slightly bigger mass of natural uranium, at least less than a ton of it, and still have a critical reactor ?

    In a word: no.

    Reactors using unenriched (natural) uranium as fuel need moderators like heavy water or graphite, (the two most common) that have better neutron cross sections than regular water.


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  8. 58
    BMS Says:

    The problem with regular (“light”) water is that, although the hydrogen atoms are excellent moderators (i.e., they’re very good at slowing down fast neutrons through collisions), they are also too good at capturing neutrons. This loss of neutrons is sufficient to prevent criticality in natural uranium. Carbon (graphite) and deuterium (heavy water) atoms provide moderation without this loss of neutrons, which is why they are used in reactors that can burn natural uranium.

    The challenge with using natural uranium is that the main isotope of this material, U-238, also absorbs a significant number of neutrons. Therefore, using more natural uranium just results in having more parasitic capture of neutrons, which prevents criticality. The only way to get around this is either to reduce the amount of U-238 (i.e., enrich the uranium) or to reduce the neutron absorbers in the moderator (i.e., switch to heavy water or graphite). There is no third way.


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  9. 59
    Frank Says:

    Just a though:
    High level waste used 50 years ago looses much of their high penetrating gamma rays radioactivity and contains nearly 2% of 235U and Pu which is enough to maintain a nuclear reaction.

    This material can be chlorinated and pyroprecessed, however the process is not cheap or easy to do but is easier than isotopic separation of 235U process. Use super critical heavy amonia (NH3) power cycle and metalic U instead of water to avoid UO2 formation.

    238U is a neutron refractive and heavy H does not. Neuton leakage has to be taken into account when the calculations are made.

    I think that at low temperatures metalic U can be used with just an electroplated coating and the reactivity can be controlled by the NH3 pressure. Higher reactivity=Higher tempearture=Less dense NH3=Lower reactivity=Pasive safety

    The steel vessel walls has to be electroplated to avoid NH3 corrosion and should not be exposed to high neutron rediation. Xe and I has to be periodically removed from the NH3 periodically to avoid reactor poisoning. In case of an accident the loss of NH3 will stop the reactor and a more effective coolant can be injected to avoid the notorius loss of coolant accident.

    The fuel can be made hexagonal forms and the coolant can run on the inside of the fuel rod (contrary to the actual reactors) to allow the NH3 work as a moderator and the 238U as neutron reflector.

    An NH3 reformer has to be included to the design and as allways, the formation of tritium is an issue that has to be addressed because it has a tendency to leak thrugh the steel.

    The recicling of materials at the end of reactor life look also easier. No graphite and metalic U is easier to process and purify than the oxides.


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  10. 60
    DV82XL Says:

            Frank said:

    High level waste used 50 years ago looses much of their high penetrating gamma rays radioactivity and contains nearly 2% of 235U and Pu which is enough to maintain a nuclear reaction.

    That’s right, in fact you can use this material without reprocessing directly in a heavy water moderated reactor like a CANDU. The “DUPIC” fuel cycle, or “direct use of spent PWR fuel in CANDU” does just that.


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  11. 61
    drbuzz0 Says:

            Brayton said:

    Hello ! Your article is extremely interesting, but I wonder if you are right about using several tons of natural uranium in order to achieve critical mass.Indeed, I live near the EPFL in Switzerland, and they got a research reactor called CROCUS, which only contains about two hundred kilograms of very low enrichment uranium (1.8% and 0.9%) and is moderated by light water.
    Wouldn’t it be possible to reproduce such a setup with a slightly bigger mass of natural uranium, at least less than a ton of it, and still have a critical reactor ?

    No amount of natural uranium will be able to achieve critical with just light water. Enriched uranium can, even if it is only slightly enriched. A sufficiently large amount of uranium enriched to just under two percent can reach critical mass with light water.

    Natural uranium requires heavy water, or possibly ultra pure graphite. you also need a sizable amount of it.

    I believe the reactor that would be the most efficient in creating critical mass from a relatively small among of unenriched uranium would likely be an aqueous homogeneous reactor, using heavy water.

    Even despite the fact that it’s smaller than most other designs, you will never build one in your kitchen or garage. Not to mention the fact that the average person is not going to be able to afford that much heavy water.


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  12. 62
    DV82XL Says:

            drbuzz0 said:

    Not to mention the fact that the average person is not going to be able to afford that much heavy water.

    To say nothing of the fact that almost all commercially available uranium sulfate or uranium nitrate is made of DU which contains less than 0.3% U-235.


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  13. 63
    Frank Says:

    The issue with natural uranium is a balance between the atoms that produce neutrons by fision and the atoms that absorbs neutrons. If a fision reaction of 235U produce 2.3 neutrons per fision average, one of the neutrons has to be conserved to maintain the chain reaction and 1.3 neutrons are available for losses.

    Using natural uranium with basically 1 atom with a fision probability of 250 and 130 atoms with absorption probability of 2.2 (this is when the neutrons are slowed down) the balance between produced and consumed are very close (1*1.3*240 130*2.2 or 312286).

    This means that the additional losses on the reactor has to be very small to sustain the nuclear reaction. This is why the heavy water is the preferred moderator for this reactor. It can be produced very pure, very good slowing down the neutrons and its absorption capacity is very small.

    The amount of material has to deal with the issue that the neutrons are produced in a very fast spectrum and tends to escape or “leak” from the fuel material. There are several ways to address this and two ways are by making a bigger reactor with less “neutron leakage” or using a material with more atoms per unit volume that can produce fision and a smaller reactor.


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  14. 64
    Frank Says:

    Correction: 1*1.3*240 is close to 130*2.2 or 312 is close to 286.


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  15. 65
    Frank Says:

    Also, Uranium Hydrade (UH3) with heavy hydrogen (Heavy H can be obtained by an electrolisys process at roughly 16 grams per gallon) can be produced by exposing metal uranium to Hydrogen at 250-300C. The compound is pyrophobic and decompose at 700C so the use of NH3 as coolant/moderator (no oxygen in the reactor core) better fits the design safety parameters of such a reactor.


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  16. 66
    drbuzz0 Says:

            Frank said:

    The compound is pyrophobic and decompose at 700C so the use of NH3 as coolant/moderator (no oxygen in the reactor core) better fits the design safety parameters of such a reactor.

    If you are not going to use enriched uranium, then it will be mandatory that the NH3 also use isotopically pure nitrogen-15. N-14 has far too high a neutron cross section.


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  17. 67
    DV82XL Says:

            Frank said:

    Also, Uranium Hydride (UH3) with heavy hydrogen…

    Various designs of self-regulating uranium deuteride nuclear reactors have been proposed off and on since the early 50s but none have gotten farther than the drawing board, because although they look good on paper, the practical aspects (particularly material selection for the containment envelope) are somewhat daunting.

    This is not a path to any kind of homemade nuclear reactor.


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  18. 68
    Frank Says:

    In a self regulating uranium deuteride the uranium has to be heated above 700C to decompose the material and recombine again at lower temperature. The chemical reaction is too slow for practical purposes, however in this case the reaction will be contrlled by the NH3 pressure or molecular density and not by decomposing the UH3.

    May be you are right and is a bad idea but I do not read any paper who test the concept this way.

    Regarding the nitrogen you are right, 15N has to be isotopically separated from 14N and the istopic concentration is low (0.37%). I do not know too much about isotopic separation and maybe the process is too dificult and expensive.

    I think about nitrogen because:
    1) Is a lot less corrosive than oxigen and is compatible with UH3
    2) Liquid nitrogen is available at $0.20/litter
    3) Has a capacity to disperse the neutrons (Scattering) 2.5 times more than Oxygen which means less nuclear
    fuel, less neutron loses, a smaller size and a cheaper reactor
    4) Neutron absorption of 15N is six times less than natural oxygen, however putity should be 99.99% or
    more to achieve oxygen performance in netron absorption.
    5) Amonia can be used more efficiently controlling reactivity and used in a power cycle than water.
    6) I think the inventory required of NH3 is much less than H2O per extracted unit of power. By this way
    the extra cost of 15N is transleted in less cost for2H.
    7) 15N should be cheaper than 2H because 15N is 0.37% nitrogen and 2H is 0.0156%
    8) It looks that NH3 can outperform water in a power cycle.

    Design a nuclear reactor is lifetime project with a lot of trial and errors. I do not know any path to safely and economically develop a home made nuclear reactor. Maybe this is the closest I can get.


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  19. 69
    Frank Says:

    NH3 cycle has another advantage.
    Because pressure and density in gases changes are very fast, in an under moderated reactor (no natural uranium) the nuclear reaction can pulse between critical and subcritical reducing the power produced, the heat to be removed and the reactor size. This can not be done with water. By taking advantage of the delayed neutrons and the slowing capacity of 2H the reactor can be operated very close to the critical point making it more controllable.
    I read something similar for an experimental reactor but I do not find the technical paper.


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  20. 70
    DV82XL Says:

            Frank said:

    Regarding the nitrogen you are right, 15N has to be isotopically separated from 14N and the isotopic concentration is low (0.37%). I do not know too much about isotopic separation and maybe the process is too difficult and expensive.

    Ultimately it boils down to two choices: you enrich the fuel, or you enrich the moderator. Yields using the standard NITROX process to enrich nitrogen are too low for this application, and at any rate one still must produce deuterium as well. While this type of reactor might work in theory, it is far too complex to be a practical route to commercial deployment.


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  21. 71
    drbuzz0 Says:

    I do not know very much about the processes used to separate isotopes of nitrogen. However, I am aware that it has been done and N15 has been obtained for nuclear purposes.

    But bear in mind, isotope separation is NEVER easy and ALWAYS energy intensive. Arguably, deuterium separation is the “easiest” and it’s not easy either, which is why heavy water is so expensive.

    It certainly can be done, but expect anything like N15 enrichment to add considerable expense.


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  22. 72
    Frank Says:

    This project is not cheap or easy but I think is feasible and it has a good potential to be cheaper and easier in the future.
    I also think a 3MW paper reactor is feasible to be designed. Comments are welcome.

    1) Heavy but not ultra pure Heavy NH3 (Cost-Benefit driven)
    2) NH3 operating near the critical point (Triple functions: Moderator, Neutron scattering, Coolant)
    3) Internal heat exchangers to maximize KW per KG ratio of heavy NH3 usage
    4) Heat used to operate a critical CO2 turbine (Technology in development)
    5) Low enriched but maximum allowed by regulations U Heavy UH3 fuel rods (Reduced size reactor)
    6) Depleted metalic U blankets (Dual functions: neutron reflector and resonant zone neutron absorber)
    7) Online remoal fuel and blanket materials (Proliferation issue?)
    8) Safety systems: Heavy water drainage, emergency stop rods, NH3 removal, UH3 decomposition,
    periodic fuel recycling for fision products removal.
    9) Ziconium for neutron exposed parts with 20 years design life
    10) Automatic fuel purification cycle by heating the fuel above 700C to remove H and melting U to remove
    fision products (Technology feasible but has to be developed)
    11) Automatic blanket transmuted material removal by melting-precipitation of U and eutectic U-Pu
    (Technology feasible but has to be developed)
    12) Modular design that can be mass produced and recycled in factories
    13) End of life reactor recycling. Reactor will have a salvage value
    14) High breeding based on cost-benefit
    15) Online Xenon and Iodine fision products extraction
    16) Online NH3 recombination and tritium extracion
    17) NH3 variable frequency turbine pump
    18) NH3 extraction and addition control system that controls core reativity (Difficut but feasible)


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  23. 73
    DV82XL Says:

            Frank said:

    This project is not cheap or easy but I think is feasible and it has a good potential to be cheaper and easier in the future.

    What I do not see here is anything that would make this idea an improvement over other GenIV designs that are out there and are further along in development. The fact is there have been several novel concepts for fission reactors that looked good on paper (that is the nucleonics worked out) that have died because the engineering was too complex for the potential gains. So even if you are able to make an argument that the physics works out (and I’m not suggesting that it necessarily does) this idea doesn’t display any compelling reasons why it should be explored.


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  24. 74
    BMS Says:

            Frank said:

    This project is not cheap or easy but I think is feasible and it has a good potential to be cheaper and easier in the future.

    Great, but why are you posting this stuff on a blog that isn’t particularly a blog about nuclear power?

    Why don’t you write up a paper about it (about ten pages would do) and submit it to ICAPP’17? If it gets through the review process, you can present your idea to experts in this field in Kyoto.


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  25. 75
    BMS Says:

    Actually, I think that you have plenty of time to make ICAPP’16, and present your ideas in San Francisco.


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  26. 76
    Krank Says:

    I’m not a scientist and this is why I do not publish in scientific forums or write scientific papers.


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  27. 77
    Frank Says:

    It looks that an alternative to heavy NH3 is heavy CH4. At the same pressure and it has better thermal conductivity, similar density and does not need carbon isotopic separation. I do not find any data about the behaviour of CH4 under a neutronic flux but it is a simple molecule that can be recombined and will not damage the reactor core if any residue accumulate in the tube walls. A recombination unit will be also necessary. CH4 is also compatible with UH3 and Zirconum metal.


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  28. 78
    DV82XL Says:

            Frank said:

    It looks that an alternative to heavy NH3 is heavy CH4.

    Even if this did work, you still have not established why it is an improvement over current technology, and it is unlikely that it would. Liquid methane is used as a moderator for neutrons produced by the pulsed neutron source at the Rutherford Appleton Laboratory in Oxford U.K.. The moderator is kept very cold but even then radiation damage effects in the methane result in the formation of carbon which deposit everywhere in the flowpath. As it stands these deposits restrict the circulation of methane, reduce efficiency, and have to be controlled for. There is nothing that commends this material for high temperature use.


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  29. 79
    Anon Says:

    CH₄ happens to be a gas with a critical temperature way less than 0°C.

    You’ll need one hell of a pressure tank to contain it at operating temperatures of a reactor that can produce power, reactors researching nuclear behaviour at cryogenic temperatures might find it useful though.

    Just like everyone else I can’t see any advantage of it over heavy water for a homemade reactor.


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  30. 80
    Frank Says:

    In my point of view (please remember that I’m no a scientist) the advantages are:
    1- Smaller reactor size – Most of the moderating effect is performed by the heavy UH3 in the fuel and in the
    blanket. The moderating capacity of H and the neutron scattering capacity of U
    makes the reactor much smaller and powerful.
    2- Higher efficient use of Hevy H – In CANDU the calandria is filled with ultrapure heavy H that is used as
    moderator and not as a working fluid.
    2- High breeding – For what I read, the cost of 10% enriched U is aproximatelly $3,000/ kg The excess
    of neutrons are captured on the blankets during in the U resonant zone and does not
    have to compete with other materials such as the fission products. By capturing the
    excess neutrons in a mid distance between fuel rods I’m not sure if this make the
    reactor operate on negative feedback. The fuel and blanket material are much more
    easy to reprocess than uranium oxide. Just heat the UH3 and it returns to a metalic
    form. The process has to be bellow $15 per blanket Kg at 0.5% transmuted to be
    economically feasible.
    3- Minimum disposing costs- Fuel is more economical to reprocess than to disposing. Fision products can have
    an economic value, spent fuel does not.
    4- More achievable operating temperatures (400C), pressures (700psi) and better material compatibility (UH3,
    Zircalloy, CH4 or NH3).
    5- Cheaper heavy H and N – The combination of U enrichment, heavy water purity, breeding capacity and reactor
    residual value (The Heavy H can be recycled at the end of reactor life and I think the
    reactor also can be recycled) can make this reactor more attractive.
    6-Reactor modularity – By making smaller modular reactors with automatic refueling and reprocessing the
    reactors can be producer cheaper.
    7-Power cycle compatibility – First generation of CO2 power cycle turbines are in the few MW range. Normal
    steam turbine are cheaper than critical pressure turbines.
    8- Safety – Has more ways to shut down pasively. Fision products are removed periodically and does not
    represent a meltdown risk.
    9- Better reaction time – Very smal over reactivity with high moderation allows the reactor to be more
    controllable.

    Regardin GEN IV:
    Lead Bismuth Fast breeder: High fuel inventory (100X gerater than thermal reactors) High cost of bismuth,
    corrosion issues (Materials can be recovered at the end of reactor life but fuel)
    Sodium Fast breeder; High fuel inventory (100X gerater than thermal reactors) risk of water-sodium mixing.
    Molten salt: Fuel purification process is complex and look costly, material compatibility at high temperature
    and corrosive environments, graphite durability, delayed neutrons produced outside the reactor
    core.

    In this concept I think that life cyle overall cost is the first stept to determine if this reactor is feasible. I do not make the math so you may be right.


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  31. 81
    DV82XL Says:

    I am sorry Frank, but none of these arguments makes much sense compared to the facts.

    To start off with radiolysis and high temperatures will destroy the methane far too quickly, and the fact that the carbon deposits out (as seen in the ISIS device mentioned above) means real trouble with recombination even if a good catalyst was available.

    Your statements about the nucleonics are pure supposition and likely false.

    Finally within the terms of the thread, Aqueous Homogeneous Reactors, (AHR) in the heavy water versions, have the highest neutron economy of all designs, (thus most compact) and are the least expensive to make, yet even they are out of the scope of DYI.

    I am sorry, these ideas simple are not very good and are fraught with serious engineering issues that makes this a dead end.


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