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  1. Personally, I believe that application of nuclear power in space would be very much in our interest. Not only do nuclear thermal rockets offer a major improvement over existing propulsion technologies, but the use of nuclear reactors as power sources for satellites, space probes, and the like could allow for much greater scientific return or utility. However, I realize that nuclear power does have associated risks, and there are others who may feel different. Whether you are for or against the usage of nuclear power in space, I am curious to hear your opinions. For reference, here's an interesting paper discussing the topic.
  2. In a joint press conference this morning, AU PM Scott Morrison, UK PM Boris Johnson and US President Joe Biden announced the acquisition of SSN and domestic nuclear manufacturing capability to replace our 6 SSK. This will substitute the previously programmed 12 “shortfin barracuda” SSNK (denuclearised barracuda SSN). This is a massive change for Australia. ADBR story ADM story ABC news story So far the reports are all saying the same thing.
  3. There's been a lot written about nuclear energy, radiation, and similar topics. Some of it is good. Most of it isn't. This thread is to post any good resources you've discovered on nuclear topics. Books, articles, random internet pages, anything useful goes here. I'll start with a couple books I've gotten out of the library at work. Most of the stuff in the work library is fairly old, but they're all pretty decent. The Health Hazards of Not Going Nuclear, by Petr Beckmann (1977) Good comparison of the relative hazards of nuclear power and continued use of fossil fuels, among other things. Also features burning hatred of Ralph Nader. Very pro-nuclear. Possibly written by a temporally displaced Collimatrix. Before It's Too Late: A Scientist's Case for Nuclear Power, by Bernard Cohen (1983) Talks about a lot of the misinformation in the world about radiation and nuclear power, as well as the actual effects of radiation compared to public perception. Pro-nuclear, with a somewhat less blunt tone than the previous book. Our Radiant World, by David Lillie (1986) Discussion of radiation in the world, due to natural sources, man-made sources (such as medical X-rays), and nuclear testing. Has good factual data on things such as radon exposure, Three Mile Island radiation releases, and other stuff. More neutral tone, moderately pro-nuclear.
  4. One of the most commons objections to the use of nuclear power is the waste produced. While nuclear energy produces much less waste by volume than other forms of energy such as coal, the unique properties of the waste mean that there are special challenges associated with disposing of it. In this topic, I'll be talking about high level waste, low level waste has far less challenges associated with its disposal. As not all fissile materials within a fuel element will be used up in a reactor, "spent fuel" (especially that which hasn't been reprocessed) still contains significant quantities of U-235. More importantly, large amounts of fission products with varying half-lives are contained in the fuel. The decay of these fission products generates significant waste heat, which provides the main short-term challenge associated with spent fuel disposal. This site; http://large.stanford.edu/courses/2012/ph241/tilghman1/ gives the following equation for the waste heat produced by spent fuel; P/P0 = 0.066 × [ (t-ts)-0.2 - t-0.2 ] By messing about with various numbers in that equation, you can see that a year after shutdown, waste heat will be about 1/1000 of reactor output. This seems trivial, but for a 1000 MW reactor, that is still 1 MW of waste heat, more than enough to melt a fuel element with no cooling mechanism. (Just as a simple calculation, a fuel element producing 50 kW of waste heat and a .5 m2 surface area in a vacuum would have an equilibrium temperature of about 1150 K). For this reason, spent fuel is usually stored underwater after removal from the reactor; this allows for convective heat transfer and for the mass of water in the pools to act as a heat sink. The water also provides the additional benefit of being a very effective radiation shield. To do list: Long term storage (WIPP, Yucca Mountain) Medium term storage (NRF, dry storage) Safety concerns associated with storage Answer any other questions as much as possible
  5. Metal cooled reactors have several advantages over pressurized water reactors. For one, their power density is greater, additionally, the coolant is unpressurized, improving safety. However, there are some downsides. The Soviets' Project 705 class submarines were powered by liquid metal reactors utilizing a lead-bismuth alloy as coolant. This alloy had a freezing temperature of roughly 400K. As a result, the reactors had to be run constantly, even while the submarines were in port (there were facilities to provide superheated steam to the reactors while the subs were docked, but they broke down and were never repaired). This reduces the lifetime of the reactor. Another coolant choice which has been used operationally is NaK (Sodium-Potassium). This alloy is liquid at room temperature, but reacts violently with water or air. I'm not an expert, but this seems like a bad thing. It seems to me that if appropriate coolants could be found, it seems that liquid metal fast reactors could see more widespread acceptance. To my untrained eye, gallium looks like a good choice. Its melting point is relatively close to room temperature (~303K), and the boiling point is quite high (over 2600K). Also, gallium is less reactive than sodium or other alkali metals. It appears that there has been some research on this topic: http://www.sciencedirect.com/science/article/pii/S0149197000000640(unfortunately, the article is behind a paywall), and it looks quite promising. Anybody have any opinions on this, or suggestions for alternative coolants?
  6. I recently began a class on nuclear rocket propulsion, and one of the first topics covered was various nuclear rocket cycles. I'll do my best to explain them using amazing MS Paint drawings and words. The first is the hot bleed cycle. In this cycle, some propellant does not go through the reactor, but is instead shunted off in a different direction. This is mixed with some of the propellant that has passed through the reactor, but not out the rocket nozzle, creating a relatively hot stream of propellant. This propellant is passed through a turbine, which then powers the fuel pump. After passing through the turbine, the propellant is exhausted overboard (on some designs this can be used for attitude control). Since the propellant that has passed through the turbine is at lower temperature than that which has passed through the reactor, some efficiency is lost. The NERVA design from the 1960s/1970s utilized the hot bleed cycle. The cold bleed cycle is similar, except no propellant from the reactor is used to power the turbine. As a result, the propellant passing through the turbine is colder, thereby reducing turbine efficiency. However, this does have the advantage of producing less thermal stress on the turbine components. However, since the mass flow through the turbine is larger, the cold bleed cycle is less efficient than the hot bleed cycle. The expander cycle cleverly avoids propellant wastage by passing all the propellant used in the turbine back into the reactor. This avoids expending propellant in the relatively low temperature turbine exhaust, and means that the expander cycle NTR has a higher specific impulse than the hot or cold bleed cycles.
  7. This article, specifically; http://businesstech.co.za/news/general/83023/south-africa-refuses-to-let-go-of-its-nuclear-explosives/ As far as I know, the uranium itself should be good for quite a while (235 has a shorter half life than 238, but 704 million years is still damn long). However, I'm not sure about some of the other components, such as the neutron sources. Po-210 only has a half life of 138 days, which means that they'd be long dead. I don't know about the specific design of South African bombs (beyond them being gun type, and therefore using HEU), or whether they have the ability to acquire neutron sources. They probably do, since they have operating reactors.
  8. Also posted here. RD-0410 The history of American efforts to develop nuclear thermal rockets is relatively well known. Similar Soviet efforts have remained far more obscure. However, during the Cold War, the Soviet Union developed and tested an advanced nuclear thermal rocket engine, designated the RD-0410. Unfortunately, relatively little English-language information about the RD-0410 can be found (at least in easily available sources). Similar to the American NERVA program, development of Soviet nuclear rocketry began in the mid-1950s. Serious research began in 1955, with development of a rocket beginning in 1956 (the people working on this project included such notable people as Kurchatov, Keldysh, and Korolev). Initially, the Soviets planned to use the nuclear rocket to power an intercontinental ballistic missile, or possible a cruise missile. However, it was quickly realized that chemical rockets were good enough for suborbital flights. As a result, by the 1960s, it was decided to develop the engine for usage in space. The engine was developed by the KBKHA bureau, which had also developed engines such as the RD-0105 (used on some derivatives of the R-7). The goal was to develop an engine with a specific impulse of roughly 800-900 seconds, double what can be achieved with normal chemical rockets. Doing this would require creating a nuclear reactor that was both very light, and capable of withstanding very high temperatures around 3000 Kelvin. I have seen a few references to a program to develop a 2,000 isp engine, but this would require temperatures (over 15,000K) well in excess of what was possible in the 1950s (or even today) for a solid core design. The test site selected for the Soviet nuclear engine was Semipalatinsk in Kazakhstan, a remote location similar to Jackass Flats in Nevada. The Soviets had already tested numerous atomic weapons (including their first in 1949 there), so the place was no stranger to nuclear activity. It appears that tests of the engine were conducted in a mine shaft approximately 150 meters deep, unlike the American NERVA, which was tested aboveground. Most likely, this was due to concerns over radiation should the engine malfunction. At some point, the engine acquired the designation RD-0410, it is less commonly known by its GRAU designation 11B91. That the engine received a GRAU designation means that it was almost certainly considered for military applications. The American NERVA had a thrust of approximately 330 kilonewtons. This was much more than the RD-0410, which had about 35 kilonewtons. This was both by design, and due to political/monetary considerations. The Soviet government had somewhat lost interest in the project once it had become apparent that the nuclear engine was not usable as an ICBM upper stage. More importantly, by developing a lower power engine, the reactor assembly as a whole would be smaller. The RD-0410, including propellant, was planned to mass roughly 15 tons when completed; putting it well within the payload capabilities of Soviet launchers like Proton. The actual engine itself weighed only about two tons. In contrast, the American NERVA was much heavier, and could only be launched by a Saturn V or similar vehicle. There were other important differences between NERVA and RD-0410. The NERVA’s fuel elements were hexagonal in cross section, with several holes drilled in them for hydrogen to pass through. Hundreds of these elements (each about an inch wide) made up the NERVA’s reactor. NERVA Fuel Elements It has been difficult to find exact information about the geometry of the RD-0410’s fuel rods, however, it appears that they had a complex shape. The fuel rods were twisted, and had a complex cross section, shaped like the petals of a flower. This was intended to lock the fuel rods together, and prevent fuel from falling out of the reactor if a few rods cracked or became dislodged. The fuel elements were made of uranium carbide, in order to better withstand the high temperatures of the core. Development and testing of the RD-0410 proceeded slowly. By 1973, America’s NERVA had already been test fired, then cancelled before actually flying. However, large scale tests of the RD-0410’s components did not begin until 1978. The test reactor was first started on March 27, 1978, and ran for 70 seconds. Gradually, the reactor was run for longer, and at higher temperatures. By 1981, the RD-0410 was running for an hour, its design duration. A specific impulse of 910 seconds was achieved; this was superior to that which was obtained with NERVA. The American Timberwind/SNTP project from the late 1980s planned to achieve similar efficiency with much higher thrust to weight, but it encountered numerous technical problems and did not reach the test stage. All accounts of the RD-0410 state that it’s testing at Semipalatinsk went very well. Originally, it was planned that the engine would fly in 1985 (likely replacing the Block D 4th stage on Proton). However, as the Soviet Union imploded during the 1980s, development slowed, then halted. Other Soviet nuclear rockets were planned, such as the RD-0411; a high thrust (~400 kN) engine that would have been used on a Mars mission, and an engine designated 11B97, which would have had the capability of either nuclear thermal or electric propulsion. However, like all other nuclear rocket programs, none of them came to be. via Astronautix, a concept for a Soviet Mars spacecraft, that likely would have used RD-0411 Important Stats: Unfueled Mass: ~2,000 kg Total Stage Mass ~14,000 kg Thrust: 35 kN ISP: 910 sec Maximum Run Time: 3600s Height: 3.50m Diameter: 1.6m Bibliography: http://www.astronautix.com/engines/rd0410.htm http://www.popmech.ru/made-in-russia/5983-k-marsu-na-reaktore-vzryvnaya-sila/ http://www.cosmoworld.ru/spaceencyclopedia/programs/index.shtml?yard.html
  9. An interesting approach to cooling the nuclear fuel; http://atomic-skies.blogspot.com/2013/10/the-liquid-jet-super-flux-reactor.html If you're able to keep your fuel cooler, you can increase your neutron flux, and with it your power density. This could be highly important in applications where you're space or mass limited. Such as, for instance, a submarine, or a rocket engine.
  10. 10 out of 10 respondents agree that having your country hit by ICBM/SLBMs is a negative experience. How, then, can we prevent such a calamity from occurring. Skillful diplomacy ballistic missile defense! But how should a country like the US go about defending against errant ballistic missiles? Can we defend against a strike by the whole of the USSR Russia's arsenal? What about a smaller country, such as the PRC, or France (those Euros look shifty). Should we try to defend military targets, such as ICBM silos and bomber bases, or civilian population centers? How are we going to kill these warheads anyway? Direct hit to kill, as GMD uses? Or nuclear tipped? Endoatmospheric or exoatmospheric interceptors? Maybe a mixture of both? Or should we use even more exotic method, such as dust defense, or a network of orbiting nuclear mines? discuss
  11. I raised an eyebrow at a comment Weaponsman made about the Iranian nuclear program: This isn't true. The vast majority of reactor designs require fuel with varying degrees of enrichment. Natural uranium is only .7% fissile material, and light water reactors typically need around 3% enriched material as fuel. The British CO2-cooled designs need about the same level of enrichment for their fuel. The Soviet RBMK used to be able to use natural uranium, but there was a hasty redesign to make them less explodey, so they cannot anymore and require fuel enriched to 2% or so. Only the CANDU reactor can use natural uranium, and even they often do not because fuel enriched to 2% makes their operation safer and more efficient. Generally speaking, designs that use natural uranium have problems with positive void reactivity coefficients. Some of the Iranian reactors are heavy water units which might be able to use natural uranium, but would be happier and safer using mildly enriched material. However, at least one of their reactors is a light water plant, which would definitely need material to function at all. Fast-neutron reactors require much more enriched fuel, usually upwards of 20% to 50%. That's still far shy of weapons' grade material, however, which is upwards of 85%. Now, I don't expect Weaponsman to know everything; although he knows an awful lot. Seriously; history, asymmetric warfare, weapons, and crypto; he knows a whole lot about those things. So I don't hold it against him at all that he doesn't have in-depth knowledge of nuclear reactor technology. In fact, Weaponsman is usually about the best, most-informed discourse on any matter it is he chooses to write about. In fact, after reading his piece I decided to do a little digging around on various public fora to see what people had to say about nuclear technology. The results were predictable, and I was filled with despair and rage. So-called policymakers clearly do not understand this shit, and it's really easy to understand. I understand it; ergo it cannot be that hard. They're all either lazy or stupid. Nothing that Obama has said about the Iranian nuclear deal gives any indication that he or his speechwriters know what enrichment is or what it does. As for the general public, I'm not convinced that the majority of them know what the word "nuclear" means. Public thinking on nuclear energy is constructed of bad, fuzzy analogies by people who lack familiarity with the most salient facts about it. Take for example this article on the international politics of uranium supply. It's obvious that the people that this article is about, and the people who wrote it are thinking of uranium as being analogous to oil; that in order to use it for power a continuous, large-volume supply of the stuff has got to be secured and guarded. But nuclear fuels are thousands of times more energy dense than chemical ones; with breeder cycles and fuel reprocessing it's hundreds of thousands of times denser, getting on a million times (theoretically it's 1.5 million times denser). That changes everything! Indeed, the technology is slowly approaching the point where it will be economically feasible to produce electrical power from uranium extracted from seawater. The logistics of supplying uranium for power are completely different than for fossil fuels, and they should not be thought of as analogous. Similar failure to comprehend energy density, you know, the thing that makes nuclear energy interesting in the first place, dominates public discourse on nuclear waste disposal, leading to vast overestimations of just how much waste is produced per unit energy. No, you're wrong, that's how fossil fuels work. Anyway, nobody knows what the fuck about anything and everything is fucked.
  12. So You Want to Build a Fission Bomb? There are many reasons why one may want to build a fission bomb. Killing communists, for example, or sending a spacecraft to one of the outer planets. Building a bomb is not easy, but it can be done (see also Project, Manhattan). Even with publicly available information. Obviously, I’m not going to detail every little bit of our hypothetical bomb down to the last millimeter of wiring. First, I don’t know all that. If I did know it, posting it here might earn me a very long vacation to ADX Florence. The stuff here is just some equations and such to give you a general impression of how the design looks. The core of our hypothetical bomb is a sphere of highly enriched uranium. We want it to be subcritical (keff<1), but not by much. The more subcritical it is, the more we have to compress it to make it critical. In a real bomb, the core is usually surrounded by a layer of dense material such as tungsten or depleted uranium called the tamper. This helps keep the core together longer, and if it’s made of U-238, you can get some extra yield from the tamper fast fissioning. To simplify our analysis, our bomb won’t have a tamper. Then, you have a bunch of chemical explosives on the outside. This is what compresses the core, and takes it from subcritical to a super prompt critical state. When the core is super prompt critical, it’s going to heat up very quickly. Within milliseconds, the uranium at the center is going to become hot enough to be a gas (at very high pressure). At the edge of the core, you’re going to have very high pressure uranium gas next to an area of very low pressure. This is going to result in the uranium gas blowing off very quickly. This results in a “rarefaction wave” forming, as the core progressively evaporates away. This rarefaction wave proceeds inward at the speed of sound, and once it gets far enough in, the core becomes subcritical, and the reaction stops. Now, I’m going to make a few assumptions. These will result in some inaccuracy in our calculations, but the results will be close enough (also, it makes everything much simpler). Here they are; 1. The super prompt critical condition of the core will terminate once the rarefaction wave reaches the critical radius (rc). 2. The super prompt critical reactivity will remain constant until the core is subcritical. 3. The core is spherical with no tamper. 4. The temperature of the core is high enough that it can be treated as a photon gas (radiation pressure is the dominant force.) 5. No energy is lost to the surroundings during the process (adiabatic). 6. Our core is made of pure U-235. Since the rarefaction wave proceeds inward at the speed of sound, the device is critical for the following period of time; Where rmin is the radius of the core at maximum compression, and a is the speed of sound. We’ll also assume the gaseous core has a specific heat ratio of 4/3, so . Since the process is adiabatic, we know the following; Where Ecore is internal energy of the core at the end of the period of prompt criticality (this is the amount of energy released in the detonation). Substitute that into the speed of sound equation, and we get Putting that aside for a moment, let’s take a look at the point kinetics equation, which describes how power increases in a reactor following a sudden increase in reactivity (our bomb is essentially a reactor that’s undergone a massive increase in reactivity); (In this case, ρ represents reactivity, instead of density. β is the fraction of fission decay products which decay through neutron emission, and Λ is the average prompt neutron lifetime.) The second term in that equation gives us the power contribution from delayed neutrons, so we can ignore in this case (the bomb will have long since detonated by the time they become a factor). Also, in the case of super prompt criticality, ρ >> β. So our equation reduces to So to get the total amount of energy produced in the core during super prompt criticality, we need to integrate the power equation over the amount of time the core is super prompt critical. If we call that time tc, we get the following expression; Where E1 is the amount of energy produced by one fission event (202.5 MeV). Substituting that into our first equation and the speed of sound expression, and then doing a bit of algebra (which I’ll leave out for the sake of brevity), we end up with this; Solving for the Ecore expression, and defining Δr as the difference between criticality radius and the radius at maximum compression; Which gives us the total amount of energy released by the detonation. The main unknowns here are the reactivity (ρ) and critical radius (rc). Fortunately, both of these are fairly easy to determine. The critical radius is the radius at which a sphere of material has a keff (ratio of neutron production to neutron absorption) of 1. ν is the average amount of neutrons produced per fission event (~2.5), Σf is the fission cross section (σf = ~1 barn for fast neutrons), D is the thermal neutron diffusion distance (.00434m for U-235), Bg is the ‘geometric buckling’, and Σa is the absorption cross section (σa=~.09 barns for fast neutrons). Convert from σf to Σf using the following formulas; Bg for a sphere can be calculated using the following formula; Setting keff to 1 and solving for r, we find that the critical radius rc is roughly 5.2cm. A sphere of U-235 of this size will have a mass of about 11.25kg. Now that we have the keff equation, determining ρ is fairly simple. Since keff is going to be higher the more you compress the core, you obviously want to compress it as much as possible. The following equation gives the amount of explosive needed to compress the core by a given amount; Escfc is the amount of energy needed to compress the core by a given amount. η is the amount of energy contained in each unit of chemical explosive (4184kJ/kg for TNT), and ε is the efficiency of the implosion process. ε is about 30% in well-designed nuclear weapons, crude designs are probably closer to 5-10%. Congratulations! Now you have (a non-trivial portion of) the knowledge you need to build a working fission device! Edit: Updated 4/24 with corrected cross sections
  13. During the Cold War, many neutral states made efforts to develop nuclear weapons. Very few of these resulted in a working bomb. One of these failures was Switzerland; http://nuclearweaponarchive.org/Library/Swissdoc.html Interestingly, the Swiss also managed to cock up their nuclear power program; http://en.wikipedia.org/wiki/Lucens_reactor
  14. The Manhattan Project gets all the glory(it deserves it), but the Soviets quickly developed their own atomic weapons. They had some help through espionage, but I think it might be another piece of McCarthyism to dismiss Soviet atomic scientists. Here is a post on the Nuclear Secrecy Blog on the early program. Good insight, but not the end-all-be-all of information on the subject. A Model of the First Lightning/Joe 1 bomb?
  15. Looking around at various information sources available to me, there's quite a lot of information on what the west though of the SS-20. Anecdotally (speaking to a family member who was a Pershing II crewman in the late 1980s), the SS-20 was generally inferior to the Pershing II (especially in accuracy), but it was generally felt that this didn't matter, due to the SS-20's quite large warhead (incidentally, according to previously mentioned family member, the main thing on the minds of Pershing II crewmen was how to quickly GTFO the launch site). I'm curious as to how the Soviets regarded the Pershing II. Was it regarded as a major threat, or was it of relatively little strategic concern?
  16. This thread is for discussion of various fusion reactions, and their utility in power generation, weaponry, and the like. Personally, I have an irrational love for hydrogen-boron fusion, for reasons that I do not understand. I should seek help.
  17. For those of you who are not familiar with him, Robert Zubrin is an American aerospace engineer and author of some note. He is probably best known for his advocacy of the 'Mars Direct' proposal, although he's also done quite a bit of work in the nuclear spacecraft propulsion field (he's the guy that came up with the NSWR). His wiki page says he's also written on other vaguely political topics, but I'm not familiar with them. Personally, I find his work on spacecraft propulsion highly interesting, and it's good that we've got somebody putting forth cogent ideas for space exploration. However, I feel that some of his ideas are a bit too optimistic, especially in regards to his Mars Direct approach. I feel that it would be more optimal to gain more experience with long term off-planet living in a location such as the moon before proceeding to Mars, while also using that time to mature techniques such as nuclear rockets to actually get to Mars. On a related note, I showed his NSWR paper to a guy I know who has some not insignificant knowledge of nuclear physics, and he was a bit skeptical. Still, in my opinion, it's infinitely better to have somebody be a bit overoptimistic about how well their ideas will work, and keeps push them forward, then a bunch of limp wristed pessimists who are afraid to send anyone beyond LEO because it might cost a few million dollars.
  18. This thread is for discussion of ICBM basing options, as outlined in the linked paper (written in 1980). While some of them seem absurd (dirigible basing!), others appear to be more realistic.
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