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!
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.
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.
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.
View blog reactions