Combat Arms 2869 Grove Way Castro Valley, California 94546-6709 Telephone (415) 538-6544 BBS: (415) 537-1777 ÉÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ» º º º BUILD YOUR OWN A-BOMB AND WAKE UP THE NEIGHBORHOOD º º º ÈÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍͼ The following article is from the April, 1979 edition of Analog Science Fiction, pages 36-52, and was written by George W. Harper. For information on subscribing to Analog Science Fiction or obtaining a back issue of this copy, please write: Analog Science Fiction/Science Fact P.O. Box 5205 Boulder, Colorado 80233 =-=-=-=-=-=-=-==-=-=-=-=-=-=-= "Some months ago the newspapers carried an item about a physics student who had designed his own A-bomb and was now in hiding lest terrorists put the snatch on him and force him to reveal the secret of a do-it-yourself bomb. A few months after that there was a TV item on "Barney Miller" where the feds impounded a private little A-bomb, which coincidentally just happened to have been put together by a college student. Now we sympathize with the fears of students who feel themselves jeopardized by their knowledge of exotic or arcane arts and we would hate to think they cannot walk the streets safely, simply because some terrorist might seize them and compel them to serve as unwilling agents of mass destruction. And since the best guarantee of their safety is to make the knowledge so public that no terrorist would even bother to impound some other person to do the job, we have decided to provide a detailed, step-by-step method of constructing an A- bomb. It is so simple that anyone who chooses -- even if he only went to the fifth grade -- can build his own. This way the undergrad students need no longer walk in fear and trembling lest they be abducted by crazies and they can all rest a little more peacefully. So if any of you have friends who feel like going into the A-bomb business, please turn them on to this article and leave the frightened college students alone. The theory of an A-bomb is simplicity itself. Merely take two masses of the right material (usually either Uranium-235 or plutonium) and hold them tightly together for a long enough period of time. Everything else occurs on its own. The basic initial problem is determination of the minimum quantity of fissile material needed to provide the bang. In this, of course, the technological expertise of the manufacturer necessarily plays a role. If you are an advanced engineering student with access to exotic materials and the most advanced triggering devices you can probably manage quite comfortably with as little as twelve pounds of U-235. For our purpose here we will assume you are not quite so capable and so will focus our attention on the sort of bomb you can construct in an ordinary home. For this type of bomb the amount of U-235 required should be in the neighborhood of thirty pounds (about the size of a baseball). Employing only easily acquired material, this type bomb should be capable of demolishing everything within a radius of one-third of a mile from ground zero and causing extensive damage out to a distance of two-thirds of a mile. Lethal exposure to radiation could occur within a radius of one and one-quarter mile and people downwind of the fall-out might be sickened up to a distance of forty or fifty miles. All in all, it would seem a most satisfactory device which, if detonated in New York City, ought to kill perhaps 250,000 people and injure another 400,000. We believe this should be more than adequate for the average terrorist and very possibly even satisfying to a general, providing it was put in the right place. But we would also have to caution against the employment of masses of U-235 exceeding some forty-five pounds. Beyond that limit the problem of putting the pieces together in a timely and efficient manner becomes too great for amateur mechanics. It would be unfortunate if you started building one of these things and it went off in your face before you finished it. Our personal preference, therefore, would be a total mass of around thirty-six or thirty-seven pounds. This will provide a comfortably large bang while also leaving a certain margin for errors of calculation in constructing the gadget. Once an adequate amount of material has been put together in one place there is a need to keep them there for a period of about half a second. The method of achieving this half-second delay is the main problem confronting the manufacturer. Whenever two masses which together will create a critical mass happen to get too close they begin a rather violent interaction. The immediate effect of this interaction is the appearance of massive quantities of energy, all pushing outward. In a small fraction of a second this energy will fling the two masses of U-235 apart. The sole result of such an unconstrained approach is a squib explosion, one which will make a mess of the immediate area but will scarcely be felt a few hundred feet away. It is assumed any self-respecting terrorist would wish for something more spectacular so our immediate task is one of devising some method which will keep the two masses of U-235 together long enough to let bigger things happen. Over the years scientists have developed a number of methods for bringing U-235 masses together and holding them there long enough for an explosion to occur. One of the first such methods, for example, required an implosion to trigger the final explosion. In this method a mass of loosely compacted U-235 was surrounded by quantities of high explosives. At the appropriate instant the explosives were detonated, compressing the U-235 and holding it in position long enough to complete the cycle (or at least this is the sketched method which appeared in the newspapers during the Rosenberg trial). We believe it probable this was not the whole story however. Even a loosely compacted mass of U-235 would be entirely too hot, both radioactively and thermally, to be handled with any comfort. More likely the U-235 (or plutonium) was first machined into several segments which together would approximate a sphere. Each segment would then be placed in a single conduit, with a graphite or other moderator separating the various segments. At the appropriate instant a simultaneous detonation of several explosive charges would propel the different segments down their conduits to an explosion chamber. While this technique is theoretically quite workable, we feel it would be entirely too difficult for terrorists to construct using home-made equipment. Achieving the sort of accuracy needed to bring all elements of the U-235 together at the precise instant needed to obtain a satisfactory explosion implies a "fail-safe" technology one or two orders of magnitude greater than most terrorists can hope to achieve. For this reason we have resolved on a simpler approach. We feel a quite acceptable device can be constructed providing the terrorist has access to a two-story building with basement, two sticks of dynamite (or the equivalent in black powder or TNT), fifteen sacks of cement, twenty cubic yards of sand and gravel and about a week to work. Total cost, apart from building rental, should be in the vicinity of $3,000 (perhaps a bit less if second hand or surplus materials are used). The final requirement, which is a bit more difficult to come by, is the necessary quantity of U-235 or plutonium. We will touch on this matter later, but for the time being we will merely assume the U- 235 is on hand. Taking things in order, the first step is to make certain the U-235 is divided into two or more approximately equal masses. Rather obviously, it was not all together when brought into the house, so we will assume it arrived in several small packages. The immediate task is to get it into a form ready to become part of an explosion. With two masses, each weighing eighteen to eighteen-and-one-half pounds, it is necessary to machine a pair of matching hemispheres. This requires an acetylene torch. Uranium has a melting temperature of approximately 3760 degrees Fahrenheit. An acetylene torch has a theoretical flame temperature of 4770 degrees Fahrenheit, and even though this theoretical limit is not reached, the flame temperature is still comfortably above the melting point of uranium. Preferably you should first construct a small kiln out of a few dozen fire bricks and employ a bellows to add air to the system, but with a bit of patience (and some luck since uranium happens to be explosively flammable) the acetylene torch ought to be entirely adequate. As the uranium melts it is allowed to flow into a hemispherical depression created out of fire clay of the sort obtainable in any ceramics outlet. Once the first hemisphere is formed and cooled it can be moved away from the kiln and the second hemisphere manufactured. It must be noted that in doing this it is highly desirable to stay well clear of the area. Uranium has a number of unpleasant characteristics. If you happen to be in the same room while it is being melted down you are certain to inhale some of the radioactive gasses, more than enough to have a decidedly adverse effect on your life expectancy, possibly reducing it to as little as a few hours. Assuming that as a terrorist you are not overwhelmingly interested in personal survival, these matters can be neglected providing you are willing to hurry a bit. Otherwise, to smelt the uranium we would suggest you employ some reasonably good servo- mechanisms, about five tons of lead and a distance of some fifty feet or so between you and the U-235 being smelted. Given this sort of protection there should be no problem, providing appropriate peripheral precautions are taken. Keeping the two chunks of U-235 well separated from one another (and in a lead casket to prevent excessive stray radiation while you are about the business of completing the bomb), we next cut a hole from the second floor down to the basement. A couple of lengths of black iron pipe are now inserted and joined so we have a three-inch cast pipe running from the basement up to the second floor. This should give about a twenty foot total length. Probably it would be a good idea to put about a six-inch plug of cement in the base of the pipe, but if your floor is very solid and the house rests on rock this may be dispensed with. Before lowering the pipe down onto the plug we put one of the U- 235 hemispheres, flat side up, atop the plug. The pipe is then seated and the first half of the bomb is complete. To assist in providing confinement we next fill the basement with a mix of sand, cement and gravel, mixing thoroughly with water from a hose in the process. Since this is to be a one-time job there is no need to make a real production of the matter. Slopping it together will do almost as well as trying to be meticulous about the whole thing. What we are really interested in is having enough external resistance around the pipe to prevent it from rupturing and scattering uranium around the basement before having it go boom. Even a semiliquid cement-sand- gravel mix will be adequate for the purpose and any additional strength will be largely wasted. We would also suggest a few sacks of cement and sand be placed around the pipe where is passes up through the first floor. This is probably not really necessary but a little extra containment may well pay off in a higher yield. When finished, this completes the receiver element of your bomb. [Note to reader: a illustration is available in the original text] Construction of the firing element is a trifle more difficult. The idea is to take the second U-235 hemisphere and place it at the top section of the pipe so it can be fired downward onto the receiver element. While the theory is simplicity itself, there are certain inherent difficulties. For one, it would be somewhat disconcerting if the trigger hemisphere slipped during the final positioning. Lacking anywhere else to go, it would promptly slide down the pipe and then come back up again. This would be self-defeating. Not only would you be dead, the publicity would be unfortunate. Terrorists who succeed only in blowing themselves up are merely amusing and not at all terrible. Our design is probably the simplest effective approach yet devised. A thin wire screen (the same sort used to keep out flies in the summer) is placed atop the bell of the pipe and then stuffed loosely down into it, taking care that three or four inches of the screen remain outside the lip of the bell. A four- foot additional section of pipe is then seated on top of the bell and welded firmly into place. For additional strength we would also suggest one or two small holes be drilled into the joined section of the pipe and steel pins inserted. [Note to reader: a second illustration is available in the original copy of Analog Science Fiction - Science Fact] Next you take a three-foot length of 2 1/2 inch copper pipe and fill it with molten lead. The second hemisphere of U-235 is then pinned into a form-fitting recess molded at the base of the lead while a steel screw-rod is drilled into the opposite end of the cylinder for a distance of perhaps a foot. The total mass of this firing unit will be between eighty and ninety-five pounds, depending on the amount of lead employed and the length of trigger pipe used. A threaded cap is then screwed onto the pipe (note the need to tap threads onto the pipe before affixing the cap). When the cap is loose enough on the threads that you can screw it on and off by hand it is then removed and a hole large enough to accommodate the heel rod of the trigger unit is drilled into the cap. Allow some six to eight inches of freedom and drill a small hole in the heel rod, making it just large enough to accept a small nail. Several nail sizes should be tried. The optimum size is a nail barely large enough to hold the complete trigger when the cap is suspended with the complete unit hanging from it. (Note: this should not be tried atop the receiver pipe!) Once such a nail has been found we are ready for final assembly. The TNT or gunpowder is flaked and placed on a small tray, ideally a coffee grounds holder from a small percolator. The flakes or powder should be carefully tamped into place and either one or two electric primers inserted. This is placed around the heel rod with a pair of firing wires running up from the primers to the outside of the unit. The whole assembly is now screwed on and your A-bomb is complete. The wires are attached to a timer switch and the lower safety pins are removed. You now have some twelve hours to leave town before the town leaves. When the timer detonates, the charge there is far more than enough force to sheer the retaining pin and drop the trigger down onto the receiver. Completely ignoring the acceleration imparted by the powder explosion, a free fall of twenty feet by a mass of ninety-five pounds will generate around 8 x 10^10 (8 times 10 to the 10th power) erg/sec of kinetic energy at the point of impact. Added to this is the thrust of the powder charge. The total kinetic force should work out to something on the order of 10 ^12 (10 to the 12th power) erg/sec; which is fully adequate to keep the two hemispheres in contact long enough to provide a thoroughly satisfactory bang. The system is simplicity itself! But in fairness to all concerned, we ought to mention a few minor problems which should be considered by anybody wishing to put one together. For example, we touched briefly on the flammability of uranium when we mentioned the acetylene torch. We should point out that any machining should be performed under a `milk' bath. `Milk,' for those not knowledgeable of machining techniques, is a milky appearing substance having many of the properties of oil but lacking its flammability. It is readily obtainable from any distributor of machine shop supplies with no questions asked. Use of this `milk' will tend to minimize risk. Actually, it would be better if the uranium were melted and machined in a pure nitrogen atmosphere, but with care and a bit of luck you will most likely be able to manage without going to any such extremes. The radiation problems are a bit more difficult to handle. U-235 has certain expotentiation characteristics which cannot be ignored. Assume for a moment that one gram of radium has a characteristic radiation constant equal to X. Two grams of radium would then have a radiation constant of 2X. Three grams would equal 3X, and so on. With either U-235 or plutonium this is not the case. It is this precise characteristic which makes them explosive while radium is not. While one gram of U-235 may have a radiation constant of 1X, two grams might turn out to have a constant of 2.5X and three grams could well top 6X, etc. This can be a problem. Since each of your hemispheres are in excess of half the critical mass they are HOT! Simply staying in the same room with one of these units for more than a few minutes is apt to be highly lethal. Inhaling air containing dust motes made radioactive by the U-235 is a reasonably quick way to saying goodbye to the world. For these reasons we would suggest some independent air supply for those working around the material. Possibly scuba gear could be used to solve the breathing problem. Solving the general radiation problem is a trifle more difficult, but with a bit of determination, some ingenuity and some luck it should be achievable. We would suggest something on the order of a lead-encased, powered "wheelchair" which can be moved around the room with the operator sitting securely inside. A small slit, covered with leaded glass, provides the needed visibility. Leaded sleeves and gauntlets will permit the operator to perform any needed mechanical actions involving the U-235 providing he is cautious and spends no more than a few minutes at a time working with the material. As an added security against stray radiation we would also suggest the laboratory be lead sheathed on both walls and floors. The basement ceiling should also be shielded with lead to avoid problems with the radiation from the receiver element. In all, probably about six to eight tons of lead would have to be used if even a minimal security is to be maintained. Since such a weight would have to be fairly concentrated it would probably also be necessary to shore up the flooring so the building doesn't collapse. Once these precautions are taken, however, you should be well prepared to go about building your bomb. There is still one more problem though; an old recipe for rabbit stew begins with the practical injunction "first catch your rabbit." Similarly, if you are going to build an A-bomb you had better get your U-235 or your plutonium. Since plutonium is a bit more difficult to lay hands on than U-235, we will begin by assuming you want to take the easiest approach and will concentrate on U-235. In this your task may have been made far simpler since any number of newspapers and other scientific commentators have repeatedly pointed out that the best available source of U-235 is the local nuclear power reactor. By now there are nearly a hundred of these scattered around the nation so all that's necessary is to go in and steal a few of the control rods, smelt them down, purify them to eliminate the nonexplosive U-238 and then build your bomb. Getting into the reactor complex is probably reasonably easy. Most campuses are only moderately guarded. Usually there is a cyclone fence of some sort and one or two security guards at the gate. It might be advisable to do a bit of discreet checking in advance to determine whether or not there are electronic guard devices around the grounds, but usually this is not the case. Under ordinary circumstances there is no point in trying to come in by the back way anyhow. Uranium has a rather considerable mass and no one person, nor even a group of several people, are apt to be able to carry out enough uranium reactor slugs to make much of a difference, particularly since they would have to be wearing protective armor to minimize the radiation hazards. As we see it the best approach is the most direct. Simply steal a truck and semi-trailer and drive right up to the gate. Take out the guards, leave a couple of your own people as substitutes and drive right up to the reactor building, remove what you wish and depart. Very simple, very direct and highly effective. But there are a few minor problems here too. The actual reactor itself is cased in a nickle-iron sphere which is immersed in a water coolant/moderator. Since every reactor has crane hoists and servo-mechanisms for use in working on the reactor during maintenance periods at least a part of the problem is already solved. These can be used to pick up the reactor core and slide it over onto a powered dolly which can then load it onto the truck. One note of caution here; if you merely hoist the reactor sphere without pulling a few of the reactor slugs or inserting the appropriate dampers it will not be possible for you to load the device onto your truck. You will be dead in a minute or two and the whole reactor will be a puddle on the floor. For this reason we would suggest you take a prisoner or two and have them instruct you in the proper technique for pulling the core and removing the reactor unit. Additionally, it would be wise to have your semi-trailer specially modified before you ever take it in. Total weight of the system being removed is somewhere in the vicinity of fifty tons, and since you would have to have at least six inches of lead shielding inside the trailer to protect the driver in the cab, the total cargo weight would gross out at about sixty-five tons. The need for additional support members in the trailer is obvious. Alternatively, if removal of the whole core unit seems impractical, and if the power plant has enough spare slugs available, you might simply remove about 1,200 pounds of reserve slugs and load them onto the truck. This is quite a bit easier, but you cannot neglect to carry along enough moderating material, either graphite or lead, to prevent the slugs from building up heat and melting through the bottom of the truck. It would be embarrassing if you got all the way home and then discovered the bottom had melted out of the truck and the contents were scattered in a radioactive straight line all the way to your hideout. Since you would probably already be dying of radioactive poisoning by now there is little the police could do to make things worse, but it would still be an ultimate humiliation. So grab the 1,200 pounds of spare slugs and mix them with about 15,000 pounds of graphite and lead. This way you should get home safely. Assuming now that you have gotten home and are not already incapacitated by the onset of radiation sickness, your next task is to set about converting the uranium slugs into A-bomb material. Nuclear power reactor slugs are enriched with U-235. Natural uranium consists of some 99.5% U-238 and some 0.5% U-235. When prepared for use in a reactor the U-238 is mixed with enough U- 235 to bring the U-235 fraction up to about 3%. This is a very considerable improvement, but it is not even approximately good enough to give you a bomb. Bomb grade uranium must consist of at least 97+% U-235, otherwise it simply cannot explode. It will get hot at 3%. If enough of the 3% mix is piled in one spot it will boil away merrily and ultimately blow itself around the room, but there is no way it can give you a genuine A-Bomb. To get one of those you have to refine the U-235 out of the mix. The 1,200 pounds of enriched slugs you acquired can be expected to provide you with the needed 36 pounds of U-235, providing you have the time, the patience and the expertise to separate it all out. Should you have any doubts of your ability to perform a total separation you should plan in advance to increase the number of slugs removed from the power plant accordingly. If you feel you can obtain something on the order to 50% efficiency you might figure on picking up 2,400 pounds. If you are more pessimistic you might plan on 33% and grab 3,600. Generally, with the best current techniques and several passes of the material, a refining efficiency of 25% is easily achievable. To go above that requires materials and equipment not apt to be available. This would suggest you ought to abduct a minimum of 4,800 pounds, with 9,600 pounds being an optimum target. Together with the shielding necessary to transport all this mass of uranium with a degree of safety you should figure on a total mass on the order of 150,000 pounds, or 75 tons. Presuming this has been taken care of and you now have secure possession of approximately 5 to 10 tons of uranium slugs, you next have the problem of finding some place (or places) to store them while you set about extracting the needed U-235. For this we suggest you rent a small warehouse and move your operation there. You may keep your two-story building as your ground-zero site, but it is showing signs of being a trifle impractical as a refinery, particularly in view of the difficulty of separating the two isotopes of uranium. As a good estimate, you should probably figure on acquiring a structure containing a minimum of 20,000 square feet of floor space if you are serious about going into the uranium refining business. It is simply too difficult to cram the needed equipment into any smaller space. After all, if it takes hundreds of acres to refine out U-235 at such places as Oak Ridge, Tennessee or Hanford, Washington, we hardly feel we are out of line in settling for a scant 20,000 square feet here. You will be cramped but it should be possible. Now that you have your floor space you have to decide which technique you are going to use to separate out the U-235. Several of these are now available, but they tend to be mutually exclusive so you must pick one at the beginning and stick with it through out. As a terrorist one of the best methods for your purposes is the gaseous diffusion approach. This was the one used for the earliest A-bombs, and in many respects it is the most reliable and requires the least sophisticated technology. It is, however, a bit expensive and does require certain chemicals apt to raise a few eyebrows. You have to start with something on the order of a dozen miles of special glass-lined steel tubing and about sixty tons of hydrofluoric acid which can be employed to create the compound uranium-hexafluoride. Once your uranium has been converted into hexafluoride it can be blown up against a number of special low-porosity membranes. The molecules of uranium- hexafluoride which contain an atom of U-238 are somewhat heavier that those containing an atom of U-235. As the gas is blown across the membranes more of the heavier molecules are trapped than the light ones. The area on the other side of the membrane is thus further enriched with the U-235 containing material, possibly by as much as 1/2% per pass. Repeat this enough times and you wind up with uranium hexafluoride containing virtually 100% core atoms of U-235. You then separate the fluorine from the uranium and arrive at a nice little pile of domesticated U-235. From there its all downhill. Since hydrofluoric acid is expensive and probably difficult to obtain without somebody asking the wrong sort of questions it would be best to steal it if you are genuinely determined on this method, either that or first steal a few million dollars, then set up your plant as a cover and not bother getting the uranium until you are ready to start the final phase of your operations. Alternatively, if you decide the gaseous diffusion method is too cumbersome, you might merely construct a breeder-reactor pile somewhere out in the woods and use the enriched uranium to create plutonium. The plutonium could then be separated out by purely chemical techniques, thereby avoiding all the difficulties implicit in the gaseous approach. Setting up a breeder pile is simplicity itself, and any of a dozen easily obtained college texts will spell out equally good methods so there is no need to go into them here. Suffice it to say there are not theoretical problems in putting a breeder reactor together. There may be a few practical problems, but if you happen to have access to a small private river, a few train car loads of sodium, a considerable quantity of stainless steel tubing and about a hundred acres of secluded land you should be able to manage it nicely. There might be a few problems in maintaining secrecy from low flying aircraft carrying radiation detectors, but if your building is properly shielded there shouldn't be too much of a problem and you might very well escape detection altogether. Should neither of these approaches appeal to you, you might consider trying your hand at some of the interesting new techniques for isolating U-235 out of a conventional mix. One of these, for example, starts with a requirement for a cryogenic magnet capable of sustaining a 20,000 gauss flux inside a liquid helium bath. From there it starts getting complicated. A simpler approach utilizes a laser separation technique. U-235, being lighter in mass than U-238, departs with a slightly different vector when excited by a laser beam. You spray a thin mist of uranium atoms at right angles through a laser beam. The U-235 is driven out at a somewhat steeper angle than the U-238 so the task is fairly simple. In principle it is easy and reliable. It is, however, a bit slow. Using any readily obtainable laser you could probably process as much as twenty pounds of uranium per day with a 12.5% efficiency. The resulting mix at the U-235 end, would probably run about 10% U-235 after the first pass so a total of nine separate runs would be needed if the material is to reach bomb grade. Assuming you started with 9,600 pounds of slugs you should be able too come up with the needed 36 pounds of 97+% pure U-235 in just under four years. This would be something of a problem in its own right. Almost certainly you would have picked up a lethal dose of radiation during the initial theft and transfer phases of the operation, so you would not have four years to complete the refinement. On this basis it would probably be wise to have at least one, and preferably two or three back-up crews of volunteers to replace you and your original crew as you die off. You will not live to see the end of your project but, with a little bit of luck and no curiosity on the part of any of your neighbors, your successors should be able to create a pretty fair bang before they too die of radiation poisoning. Should you anticipate serious difficulty in finding enough volunteers to carry through a long range project of this sort you might consider a few other alternatives. One of the more attractive, darkly hinted at by Ralph Nader and other such reliable sources, is considerably more direct. Rather than raiding the reactor plant and stealing the uranium, why not merely short-circuit the safety systems so the station itself goes up, taking a few square miles, plus you, along with it, or at least poisoning the neighborhood with some thoroughly nasty radiation? This is a good idea. We recommend it, both for the directness of approach and the simplicity. Why go through all the bother of acquiring and refining tons of reactor-grade uranium just to get a few pounds of bomb-grade U-235? Of course there is the fact that it is only reactor-grade stuff, which means there is no possible way for you to get an explosion out of the thing. That is simply impossible no matter what you do. But this does not mean you could not come up with a distinctly impressive melt-down which will release all sorts of radioactivity in the neighborhood. Should you decide on this you will have to make definitive advance plans and work with split second timing, otherwise you are apt to discover all your efforts have gone for naught. The basic problem here is that most of the data concerning nuclear reactors comes either from newspaper reporters or Ralph Nader, and as such they ought to be accepted uncritically or not at all. As we mentioned earlier, the core unit of a reactor consists of uranium slugs and moderators in a stainless steel sphere. As the moderator rods are slipped out of the reactor, the neutrons released by decaying U-238 and U-235 atoms are captured by other atoms, triggering fissions there too. The trouble is, the process is relatively slow since the U-238 atoms are reasonably stable. The result is the sort of a chain reaction which cannot complete a real explosion. All it can do is build up heat and expand somewhat so the space between atoms serves as its own moderator. The reactor itself produces power essentially as a steam generator. The heat of the core is used to create superheated steam which in turn drives turbines. To prevent overheating, the core is placed in a special sink which floods automatically whenever the temperature starts to exceed a critical level. As there are also automatic moderator control rods and equally automatic fuel-slug removal devices, this water flooding system seldom requires any sort of attention. It is merely a third level back-up in case the first two fail. In order to force a melt- down, therefore, it is necessary to override the automatic slug removal system, the automatic moderator system and the flooding system. Once this is done the meltdown goes to completion. Now comes the question of specific goals in mind. Are you, as a terrorist, primarily interested in causing a maximum amount of immediate dislocation in society? Are you rather more interested in knocking a nuclear power plant out of operation for some indefinite period of time? Is your concern with proving a point, say that you don't like nuclear power and that you wish to convince everyone it is simply too dangerous to play with? Assuming you are mainly interested in causing a maximum immediate dislocation, it would probably be easier and simpler just to dynamite a few hundred high-tension power lines coming into New York City. Two dozen, strategically placed conventional small bombs would probably black out everything from Washington, D.C. north. A day or two would be required to mend matters and by that time you could be ready to blast some more. This would be genuinely effective! It could seriously inconvenience 35 million people for a whole summer if done properly. On the other hand, if a solitary nuclear plant were disrupted there is a good likelihood no one would even notice. Power from other sources would automatically be fed into the grid and things would go on much as before. A few months later, say in the middle of winter, there might be a shortage of power to some industrial plants, but the overall direct effect would be negligible. If your purpose is limited to knocking out the power plant for an indefinite period, then by all means tackle the main place. When the newspapers catch up with the story the nation will be deluged with panic headlines about the "narrowly averted" tragedy so the resulting publicity will be highly rewarding to your successors in the movement. Apart from the fear generated, about all it will do is prompt the authorities to take additional precautions to make it more difficult for the next group to break in. Since terror works best when it becomes cumulative this would appear to be a bit self-defeating. A persistent blasting of high- tension lines would be more effective in the long run. So we assume your concern is in proving a point. You want to demonstrate conclusively that nuclear power cannot be permitted in America. You wish to generate so much fear and horror that every plant will be closed down and the nation will rise up in arms against the "Atomic Monster." You wish to knock out a nuclear power plant and do it in the most deadly manner possible, releasing clouds of radioactivity over the neighborhood and killing as many people as you possibly can. This is something entirely different from a mere disruption of the plant and an uncomplicated core meltdown. To explain, suppose you simply pull all the safety systems and let the thing take off on its own. Temperature inside the steel core immediately starts building up. Within three or four minutes the steel around the core turns cherry red, then becomes white hot. In another minute it would commence deforming and flowing as the melting point of steel was reached. Within minutes it would be a bubbling puddle on the floor of the reactor chamber. Mostly the puddle would consist of iron, nickle, chromium, U-238, U-235, graphite and some odds and ends of other elements, including minute quantities of plutonium plus fission end-products. Still the heat continues to build until the uranium starts vaporizing as a high density "steam." As each atom of uranium is flung outward the distance between it and each other atom of uranium naturally increases, and with the increased distance the probability of neutron capture decreases. This cools the mass and reduces the temperature. In general, the distance factor for the radioactive material can be calculated to a good degree of precision. We assume a vaporization temperature for uranium at around 4,500 degrees Fahrenheit. We also assume the sphere was formed from Durimet B, which consists of: 48% iron, 35% nickle, 12% chromium, 5% silicon and a trace of carbon. The melting point of Durimet B is right at 4,950 degrees Fahrenheit. These two factors, when combined, provide for an understanding of the meltdown physics. Since the sphere containing the fission material melts at a higher temperature then the contents, once the safeguards have been disrupted the core rapidly becomes molten. The heat continues building up until the outer sphere melts, releasing the core material. Once the core material has escaped, however, the metal of the sphere quickly solidifies. But since it is lighter than the uranium it forms a crust atop the still molten fission material. This gives us three different areas to consider, the molten substance which consists of uranium, the surface crust consisting of iron, nickle and chromium, and the diffused uranium which escaped as a vapor before the crust formed. Somewhere in this mix there are also a number of fission byproducts, but for the most part they can be neglected. The uranium trapped beneath the solidified container metals will remain extremely hot until it is broken up and separated so it can cool. A surface temperature in the vicinity of 3,000 degrees Fahrenheit is a reasonably good estimate. But so far as radiation hazards are concerned there is not much to worry about. The region immediately around the reactor room will remain unusable for a year or so while automated machinery picks up the pieces and takes them out for refining, but it is not going to hurt anyone outside. Only that portion of the radioactive material which escapes the reactor complex and gets out into the surrounding countryside is going to be able to cause casualties, and with a conventional meltdown most of the material which could escape is going to be buried under the solidifying nickle-iron- chromium jacket. Only if you can get the uranium on the outside of the jacket, so it vaporizes and escapes first, will you be able to do much. Since we presume you want to release as much radioactivity as possible, this means you must also take some secondary steps. One of these might be to break into one nuclear power plant and steal as many fuel rods as you can. Then bring them over to a second plant and place them around the core before starting the meltdown. This would be effective and you could die happy in the knowledge your martyrdom probably killed fifty or sixty people in the hundred or so acres downwind of the complex. A second, and even more effective plan, would be to break into some military installation and simply steal one of their A-bombs. Bring this into the power station and you find you have achieved a genuine bang. Of course, if you've broken into the military installation and already have your own A-bomb then there is really very little reason to go through all the other rigamarole with the power station to begin with. Just take your little treasure, figure out how the trigger operates and set it off. Alternatively, if you find it too difficult to obtain an A- bomb from the U.S. military, you might try to contact the Palestine Liberation Organization, the Red Brigades in Italy or the Provisional Irish Republican Army in Belfast. These are all well-financed, well-organized groups which have been in existence for years. Since we have shown how simple it is for you to build your own A-bomb, then rather obviously they must have a few dozen of their own stashed away in the woods somewhere and since they are not using them surely they would be willing to offer you one or two in a good cause. Should they prove to be selfish about the whole thing and pretend they have none of their own then you will either have to fall back on one of the alternatives I have suggested here or set about creating a terror weapon which does not involve nuclear weaponry. In this regard may I suggest biological warfare. Several years ago the United States discontinued its research in germ warfare and presumably dumped its supplies. Since it is necessary to perform enough research to know what sort of plagues you can manufacture before you can discover how to stop the plagues someone else manufactures then there is every likelihood the nation would be virtually defenseless against a first-class biological attack. Spray a little anthrax bacillus in the air-conditioning system of the U.N. building, for instance, and within a week or so people will be dropping like flies. Let a few thousand people die in an artificial plague of this sort and the panic would easily match that of an A-bomb, and it would certainly be a lot easier to make.