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Quoted: My favorite thing about those photos is the coke bottle. View Quote View All Quotes View All Quotes Quoted: My favorite thing about those photos is the coke bottle. These photos were a recreation by another scientist of the methods that were used, but without an active core. There were no photos of the actual experiment that killed the scientist. |
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Quoted: Plus long half life of most of the material means low decay rate and low dose rate. This post does not advocate that arfcom play with their pu239 cores bare handed as was done under ww2 war time practice View Quote View All Quotes View All Quotes Quoted: Quoted: Alpha emitters are boring unless ingested This post does not advocate that arfcom play with their pu239 cores bare handed as was done under ww2 war time practice Oh fuggggg XDDDDDD I need to change some things. |
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Quoted: Serious question here: How was he not exposed to all sorts of radiation anyway just handling a plutonium ball in close proximity? View Quote Little radiation is emitted from pure plutonium, other than alpha particles. Alpha particles are stopped within the material, or by the nickel plating on the outside of the ball. "Dirtier" grades of plutonium have more of the isotope Pu240, which has a high rate of spontaneous fission, which increases the external radiation. Still nothing like a high-level radioactive element like Cobalt 60. And yes, plutonium is a radiation hazard if you ingest/inhale it, so that it's in direct contact with internal body tissues, same as any alpha emitter. Polonium is the highest intensity alpha emitter and famously used as a poison by the Soviet Union and Russia. |
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Quoted: The story of nuclear fission is the story of a free neutron interacting with a heavy element. Heavy elements are those with automatic masses (the sum of its protons and neutrons) greater than 200. The most common heavy elements we think of are usually Uranium and Plutonium as they are two that work the best in reactors and bombs; Which are typically what we use fission for. When a free neutron travels at just the right speed and distance from a heavy elemental atom of let’s say Uranium 235 (92 Protons with 143 Neutrons in its nucleus), the free neutron can be absorbed into the nucleus and immediately cause it to become unstable and split into two smaller “daughter” nuclei. These can be a number of different smaller elements, but usually two and sometimes three. One possible product of a U235 fission is 1 Beryllium 145 atom and 1 Krypton 92 atom. In addition to these two new daughter nuclei, the reaction also produced thermal light energy and 3- free neutrons. These free neutrons produced by the fission reaction have the potential to cause more fissions. In fact this is why nuclear physics was so heavily studied in the early to mid 20th century, the possibility of these free neutrons causing a chain reaction, releasing exponentially more energy than a chemical reaction. If you have enough fissionable material, such as U235, in a small enough space, a series of fissions by the released neutrons from the first fission event can become a sustainable chain reaction. The term for this is when the reaction becomes “critical”. The daughter elements produced by each fission are always unstable and highly radioactive, releasing alpha particles, which is two protons and two neutrons (a helium nucleus) or beta particles (a high speed electron) which changes these 1st generation daughter atoms into smaller, more stable atoms. It is important to note that all elements heavier than Iron release more energy from their fission than it takes to produce the reaction. All elements smaller than Iron requires more energy to produce a fission reaction than what is released from the reaction. All atoms can be split or fissioned, but you only get a net positive energy release from the heavy ones. View Quote Wow, I didn't know the last part that only heavy atoms can release net energy from fission. That's cool, thanks for the summary. |
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Quoted: Bottom photo is likely Slotin, who was warned his carelessness with criticality demonstrations would get him killed. View Quote View All Quotes View All Quotes Quoted: Bottom photo is likely Slotin, who was warned his carelessness with criticality demonstrations would get him killed. Quoted: "Demon Core" https://upload.wikimedia.org/wikipedia/commons/1/13/Partially-reflected-plutonium-sphere.jpeg Harry Daghlian https://upload.wikimedia.org/wikipedia/commons/0/0e/Daghlian-hand.jpg During an experiment on August 21, 1945, Daghlian was attempting to build a neutron reflector manually by stacking a set of 4.4-kilogram (9.7 lb) tungsten carbide bricks in an incremental fashion around a plutonium core. The purpose of the neutron reflector was to reduce the mass required for the plutonium core to attain criticality. He was moving the final brick over the assembly, but neutron counters alerted Daghlian to the fact that the addition of that brick would render the system supercritical. As he withdrew his hand, he inadvertently dropped the brick onto the center of the assembly. Since the assembly was nearly in the critical state, the accidental addition of that brick caused the reaction to go immediately into the prompt critical region of neutronic behavior. This resulted in a criticality accident. Daghlian reacted immediately after dropping the brick and attempted to knock the brick off the assembly without success. He was forced to disassemble part of the tungsten-carbide pile in order to halt the reaction. Daghlian was estimated to have received a dose of 510 rem (5.1 Sv) of neutron radiation, from a yield of 1016 fissions. Despite intensive medical care, he developed symptoms of severe radiation poisoning, and his sister and widowed mother were flown out to care for him. He fell into a coma and died 25 days after the accident. He was the first known fatality caused by a criticality accident. His body was returned to New London, where he was buried at Cedar Grove Cemetery. https://upload.wikimedia.org/wikipedia/commons/d/db/Tickling_the_Dragons_Tail.jpg That's what I thought too... Some people here may find it interesting that if you make liquid solutions of compounds containing fissile materials, that the liquid can go critical if you get too much of it in the same place. These liquids are prepared during the process of enrichment and manufacturing. Here is a tip: If you were careless and accidentally caused a small criticality event by filling a specialty container to the wrong level for the concentration of solution you were using, DON'T try to hide your mistake by pouring the entire container down the floor drain, (which isn't designed to prevent criticality) and thus causing an even larger criticality event that drenched you in radioactive liquid. Yes, nuclear physics and fissile materials are very interesting! Sometimes in the Chinese way. Carpentry: Measure twice, cut once. Fissile Liquids: Measure twice, pour once. |
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There are some atoms that are very large. So large that they spontaneously fly apart into smaller particles. In nuclear fusion we just help that process along more easily by shooting neutrons into them. The difference in mass is released is energy.
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Quoted: As you know, when atoms are split, there are a lot of pluses and minuses released. Well, we've taken these and put them in a huge container and separated them from each other with a lead shield. When the box is dropped out of a plane, we melt the lead shield and the pluses and minuses come together. When that happens, it causes a tremendous bolt of lightning and all the atmosphere over a city is pushed back! Then when the atmosphere rolls back, it brings about a tremendous thunderclap, which knocks down everything beneath it. View Quote "Tremendous bolt of lightning" sounds very very frightening. |
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There are some atoms that are very large. So large that they spontaneously fly apart into smaller particles. In nuclear fusion we just help that process along more easily by shooting neutrons into them. The difference in mass is released is energy.
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Wow. actually some good answers in this thread.....just a few amongst the yuk-yuk-hyuk boyz LOL.
Uranium ore needs to be processed to concentrate it before it's suitable for use as a nuclear fuel or in a weapon. Look up gaseous diffusion/centrifuge processing. Uranium U235 and Plutonium U238 are different elements. U235 is commonly used to fuel nuclear reactors and is enriched (Processed as in above) to 20 percent or so. Weapons grade you need 90 percent. Or so. LOL. The demon core story is a good read and is instructive. Mr Slotin's death provided information on contamination and exposure rates that actually saved lives down the road. Nuclear reactors are controlled just so with the use of control rods that moderate or stop the fission process. The reactor generates heat, turning water pumped through it to steam. That runs turbines that generate electricity. Shazzam! If the control rods are completely withdrawn, depending on the reactor design, the reactor will heat up beyond it's design specs and basically melt. Others more knowledgeable can speculate on a typical BWR going hiroshima. Another true story like the demon core that is worth a read is the SL-1 reactor story. Yeah. The three operators that were there when that reactor went critical are buried under tons of rock with the reactor when the site was cleaned up. Reactors typically melt because forming a critical mass, where the reaction is self sustaining and releases ALL of it's energy at once instead of "heating" is prevented by its design. Usually. If you want to understand how nuclear weapons work, learn the story of Fatman and Littleboy first. Two main designs. Those are the original two basic fission weapons. The Little Boy is a gun-type weapon. Calculate a critical mass for the U235 you have. (like Mr Slotkin's experiment but without the POOF!!!) Divide that mass in a device far enough apart that they do not form a critical mass. To detonate the two cores are driven together with explosives. Portable Sunshine is created. The Fatman design is an implosion device. Create a hollow sphere of U235, or another shape, even a solid probably round mass that's not a critical mass until you crush it into a smaller symetrical shape that IS critical. To do this you use a high grade of explosives that have to be triggered in a specific way. Simply stuffing a bomb casing fulla dynomite around a core no-workee. It has to be a very precisely triggered IMPLOSION. Fusion is different. They pretty much all start with a fission explosion that triggers a second stage that creates a fusion explosion that releases even more energy. Since this stuff is declassed, unlike when I learned about it in 1970's Army, all of this info is out there and the YouTube videos alone are worth the watch. Operation Castle Upshot Knothole Operation Plumbob to start. It's far more instructive to do that and a lot more fun. |
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Quoted: Reactors typically melt because forming a critical mass, where the reaction is self sustaining and releases ALL of it's energy at once instead of "heating" is prevented by its design. Usually. View Quote Attached File There is no "reacting" in a reactor unless there is a critical mass. "releasing all its energy at once" is a fast fission chain reaction which makes a bomb, which is not possible in a reactor for several reasons. No Chernobyl was not an atomic bomb. Meltdowns happen because there is insufficient coolant to absorb the energy output. Lots of ways to get there, but that's the gist of it. |
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Quoted: /media/mediaFiles/sharedAlbum/n725075089_288918_2774-532.jpg There is no "reacting" in a reactor unless there is a critical mass. "releasing all its energy at once" is a fast fission chain reaction which makes a bomb, which is not possible in a reactor for several reasons. No Chernobyl was not an atomic bomb. Meltdowns happen because there is insufficient coolant to absorb the energy output. Lots of ways to get there, but that's the gist of it. View Quote View All Quotes View All Quotes Quoted: Quoted: Reactors typically melt because forming a critical mass, where the reaction is self sustaining and releases ALL of it's energy at once instead of "heating" is prevented by its design. Usually. /media/mediaFiles/sharedAlbum/n725075089_288918_2774-532.jpg There is no "reacting" in a reactor unless there is a critical mass. "releasing all its energy at once" is a fast fission chain reaction which makes a bomb, which is not possible in a reactor for several reasons. No Chernobyl was not an atomic bomb. Meltdowns happen because there is insufficient coolant to absorb the energy output. Lots of ways to get there, but that's the gist of it. "You can't put too much water into the reactor." Ed Asner |
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I believe popcorn is actually a really really tiny nuclear explosion.
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Quoted: Wow. actually some good answers in this thread.....just a few amongst the yuk-yuk-hyuk boyz LOL. Uranium ore needs to be processed to concentrate it before it's suitable for use as a nuclear fuel or in a weapon. Look up gaseous diffusion/centrifuge processing. Uranium U235 and Plutonium U238 are different elements. U235 is commonly used to fuel nuclear reactors and is enriched (Processed as in above) to 20 percent or so. Weapons grade you need 90 percent. Or so. LOL. The demon core story is a good read and is instructive. Mr Slotin's death provided information on contamination and exposure rates that actually saved lives down the road. Nuclear reactors are controlled just so with the use of control rods that moderate or stop the fission process. The reactor generates heat, turning water pumped through it to steam. That runs turbines that generate electricity. Shazzam! If the control rods are completely withdrawn, depending on the reactor design, the reactor will heat up beyond it's design specs and basically melt. Others more knowledgeable can speculate on a typical BWR going hiroshima. Another true story like the demon core that is worth a read is the SL-1 reactor story. Yeah. The three operators that were there when that reactor went critical are buried under tons of rock with the reactor when the site was cleaned up. Reactors typically melt because forming a critical mass, where the reaction is self sustaining and releases ALL of it's energy at once instead of "heating" is prevented by its design. Usually. If you want to understand how nuclear weapons work, learn the story of Fatman and Littleboy first. Two main designs. Those are the original two basic fission weapons. The Little Boy is a gun-type weapon. Calculate a critical mass for the U235 you have. (like Mr Slotkin's experiment but without the POOF!!!) Divide that mass in a device far enough apart that they do not form a critical mass. To detonate the two cores are driven together with explosives. Portable Sunshine is created. The Fatman design is an implosion device. Create a hollow sphere of U235, or another shape, even a solid probably round mass that's not a critical mass until you crush it into a smaller symetrical shape that IS critical. To do this you use a high grade of explosives that have to be triggered in a specific way. Simply stuffing a bomb casing fulla dynomite around a core no-workee. It has to be a very precisely triggered IMPLOSION. Fusion is different. They pretty much all start with a fission explosion that triggers a second stage that creates a fusion explosion that releases even more energy. Since this stuff is declassed, unlike when I learned about it in 1970's Army, all of this info is out there and the YouTube videos alone are worth the watch. Operation Castle Upshot Knothole Operation Plumbob to start. It's far more instructive to do that and a lot more fun. View Quote U235 does not need to be enriched to 20% to fission in a light water reactor. It can be enriched to much lower levels than that and still work in a light water reactor. Natural uranium, meaning completely unenriched uranium can be used for fuel in CANDU reactors. Commercial nuclear reactors can melt down and chemical or steam explosions can occur, but they can't have a nuclear bomb type explosion. Reactors accidents can involve different mechanisms that don't involve uncontrolled fission. At Idaho National Engineering Lab, there was an accident in an experimental reactor involving a control rod being manually pulled out way too far which made the reaction rate skyrocket. So that one qualifies as uncontrolled fission. Three Mile Island, was a loss of coolant accident, which resulted in a partial melt down. Fukashima reactors were shut down and no longer having nuclear reactions. The accident occurred because the coolant pumps could no longer be run since the on-site backup generation was inoperable and all other means of powering the coolant pumps were destroyed. Since the coolant pumps were inoperable, the decay heat from the shut down reactor could not be removed and that decay heat was enough to cause all the subsequent accidents. Decay heat of a commercial reactor like Fukashima is considerable. |
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Quoted: U235 does not need to be enriched to 20% to fission in a light water reactor. It can be enriched to much lower levels than that and still work in a light water reactor. Natural uranium, meaning completely unenriched uranium can be used for fuel in CANDU reactors. Commercial nuclear reactors can melt down and chemical or steam explosions can occur, but they can't have a nuclear bomb type explosion. Reactors accidents can involve different mechanisms that don't involve uncontrolled fission. At Idaho National Engineering Lab, there was an accident in an experimental reactor involving a control rod being manually pulled out way too far which made the reaction rate skyrocket. So that one qualifies as uncontrolled fission. Three Mile Island, was a loss of coolant accident, which resulted in a partial melt down. Fukashima reactors were shut down and no longer having nuclear reactions. The accident occurred because the coolant pumps could no longer be run since the on-site backup generation was inoperable and all other means of powering the coolant pumps were destroyed. Since the coolant pumps were inoperable, the decay heat from the shut down reactor could not be removed and that decay heat was enough to cause all the subsequent accidents. Decay heat of a commercial reactor like Fukashima is considerable. View Quote Solar is safer. |
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Quoted: Wow. actually some good answers in this thread.....just a few amongst the yuk-yuk-hyuk boyz LOL. Uranium ore needs to be processed to concentrate it before it's suitable for use as a nuclear fuel or in a weapon. Look up gaseous diffusion/centrifuge processing. Uranium U235 and Plutonium U238 are different elements. U235 is commonly used to fuel nuclear reactors and is enriched (Processed as in above) to 20 percent or so. Weapons grade you need 90 percent. Or so. LOL. The demon core story is a good read and is instructive. Mr Slotin's death provided information on contamination and exposure rates that actually saved lives down the road. Nuclear reactors are controlled just so with the use of control rods that moderate or stop the fission process. The reactor generates heat, turning water pumped through it to steam. That runs turbines that generate electricity. Shazzam! If the control rods are completely withdrawn, depending on the reactor design, the reactor will heat up beyond it's design specs and basically melt. Others more knowledgeable can speculate on a typical BWR going hiroshima. Another true story like the demon core that is worth a read is the SL-1 reactor story. Yeah. The three operators that were there when that reactor went critical are buried under tons of rock with the reactor when the site was cleaned up. Reactors typically melt because forming a critical mass, where the reaction is self sustaining and releases ALL of it's energy at once instead of "heating" is prevented by its design. Usually. If you want to understand how nuclear weapons work, learn the story of Fatman and Littleboy first. Two main designs. Those are the original two basic fission weapons. The Little Boy is a gun-type weapon. Calculate a critical mass for the U235 you have. (like Mr Slotkin's experiment but without the POOF!!!) Divide that mass in a device far enough apart that they do not form a critical mass. To detonate the two cores are driven together with explosives. Portable Sunshine is created. The Fatman design is an implosion device. Create a hollow sphere of U235, or another shape, even a solid probably round mass that's not a critical mass until you crush it into a smaller symetrical shape that IS critical. To do this you use a high grade of explosives that have to be triggered in a specific way. Simply stuffing a bomb casing fulla dynomite around a core no-workee. It has to be a very precisely triggered IMPLOSION. Fusion is different. They pretty much all start with a fission explosion that triggers a second stage that creates a fusion explosion that releases even more energy. Since this stuff is declassed, unlike when I learned about it in 1970's Army, all of this info is out there and the YouTube videos alone are worth the watch. Operation Castle Upshot Knothole Operation Plumbob to start. It's far more instructive to do that and a lot more fun. View Quote US commercial reactors are enriched to no more than 5% U235. US westinghouse PWRs run "all rods out" and use dissolved boron in the coolant to control reactivity. AP1000s are boron free but use some other type of rod in place of the "chemical shim." No western designed reactor (or their copies) can "go Hiroshima." |
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Quoted: Serious question here: How was he not exposed to all sorts of radiation anyway just handling a plutonium ball in close proximity? View Quote The dome he was holding over the ball captures that small amount and reflects it back into the Plutonium. The more completely it's covered the more gets reflected back and more fission events are triggered as a result. Even a small gap is enough to keep the radiation at "safe" levels. But if it were to get entirely covered the number of fission events would increase exponentially and quickly produce lethal doses of radiation. The few seconds it was covered was enough to kill everyone in the room. Also not all radiation is as dangerous as other types. Light is radiation. The heat you feel from a distant explosion... or the Sun... or a heat lamp... is radiation. When you get an X-ray... that's radiation. Then gama rays... All those are Light, only at different wavelengths and thus energies. There's electron radiation... If you ever watched CRT TVs you were being shot with an Electron beam the whole time. Then there's ionizing radiation... I might be combining types here I'm not too sure... As I understand it... Naked Protons and also Neutrons get ejected from the reaction at nearly the speed of light. These "heavy" particles can strike other atoms such as those in your DNA and break things. Most deaths from radiation happen due to exposure to Ionizing radiation. |
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1. Radiation History to the Present — Understanding the Discovery of the Neutron |
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Quoted: The plutonium ball on its own slowly emits small amounts of radiation. The dome he was holding over the ball captures that small amount and reflects it back into the Plutonium. The more completely it's covered the more gets reflected back and more fission events are triggered as a result. Even a small gap is enough to keep the radiation at "safe" levels. But if it were to get entirely covered the number of fission events would increase exponentially and quickly produce lethal doses of radiation. The few seconds it was covered was enough to kill everyone in the room. Also not all radiation is as dangerous as other types. Light is radiation. The heat you feel from a distant explosion... or the Sun... or a heat lamp... is radiation. When you get an X-ray... that's radiation. Then gama rays... All those are Light, only at different wavelengths and thus energies. There's electron radiation... If you ever watched CRT TVs you were being shot with an Electron beam the whole time. Then there's ionizing radiation... I might be combining types here I'm not too sure... As I understand it... Naked Protons and also Neutrons get ejected from the reaction at nearly the speed of light. These "heavy" particles can strike other atoms such as those in your DNA and break things. Most deaths from radiation happen due to exposure to Ionizing radiation. View Quote In the second incident, one dead in 9 days due to radiation. The others died much later. You can look at the dose rates and see that many lived very long times and into advanced age and the causes of death is not a smoking gun for radiation. Some died due to causes that weren't radiation, but if they lived longer, who knows. |
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Quoted: Very fast moving particles (though not too fast) hit the nucleus of big atoms. The big atoms break apart and release a ton of energy. Do with that energy what you want. View Quote This is perfect. Especially the “not too fast” part. Graphite for the win. Or water if you’re in the west. |
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Quoted: Fission is separation. Fusion is combination. View Quote Gasoline, Coal, diesl ect make 2.5-5ish units of energy per unit of coalC gas, Diesel, input. Fission breaks apart uranium and makes say 1000000(I might be an order of magnitude Or 3 low)Units of energy per Unit of uranium. Fusion makes energy by combing hydrogen atoms to make helium, it yields something like 10000000000000000 units per unit of hydrogen input. Nukes are fission, the sun is fusion. |
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Quoted: Gasoline, Coal, diesl ect make 2.5-5ish units of energy per unit of coalC gas, Diesel, input. Fission breaks apart uranium and makes say 1000000(I might be an order of magnitude Or 3 low)Units of energy per Unit of uranium. Fusion makes energy by combing hydrogen atoms to make helium, it yields something like 10000000000000000 units per unit of hydrogen input. Nukes are fission, the sun is fusion. View Quote View All Quotes View All Quotes Quoted: Quoted: Fission is separation. Fusion is combination. Gasoline, Coal, diesl ect make 2.5-5ish units of energy per unit of coalC gas, Diesel, input. Fission breaks apart uranium and makes say 1000000(I might be an order of magnitude Or 3 low)Units of energy per Unit of uranium. Fusion makes energy by combing hydrogen atoms to make helium, it yields something like 10000000000000000 units per unit of hydrogen input. Nukes are fission, the sun is fusion. Thermonukes are fusion too. |
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Quoted: Crudely speaking (1) An atom consists of a nucleus comprising protons and neutrons surrounded by a sea of electrons (2) A proton has a positive charge, an electron has a negative charge and a neutron is neutral (3) A stable atom is in effect balanced with respect to protons and electrons (positive and negative attracted to each other) and the spacing between the nucleus and its orbiting electrons is energy dependant e.g. an electron close to the nucleus will require a lot of energy to remove it (stronger force of attraction) relative to an electron a long way from the nucleus (weaker force of attraction). (4) By splitting the atom nucleus with a fast moving neutron you release some of the energy that held it together and form two new nuclei (two new elements) (5) A large atom, with large numbers of protons and electrons (e.g. Plutonium has a nucleus containing 94 protons) if split by a neutron, will release more energy than a small atom. (6) The energy released being proportional to the mass and the speed of light squared. (7) On splitting the atom, neutrons will be released that move on to split other atoms (8) In a nuclear reactor the fission process is moderated by the use of graphite, the graphite absorbs neutrons and thereby limits the fission process. If sufficient graphite rods are inserted into a reactor they will absorb all neutrons and terminate the fission process. Conversely, if the reactor core is not moderated, the rate of fission increases exponentially to the point where it can no longer be moderated and you get Chernobyl. View Quote Figures! It takes somebody from Australia to explain what nobody else here could try to do without mentioning "Mommy", "Daddy", "shit" or "fuck". He probably also didn't mug his teacher back in grade school. |
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Quoted: Figures! It takes somebody from Australia to explain what nobody else here could try to do without mentioning "Mommy", "Daddy", "shit" or "fuck". He probably also didn't mug his teacher back in grade school. View Quote View All Quotes View All Quotes Quoted: Quoted: Crudely speaking (1) An atom consists of a nucleus comprising protons and neutrons surrounded by a sea of electrons (2) A proton has a positive charge, an electron has a negative charge and a neutron is neutral (3) A stable atom is in effect balanced with respect to protons and electrons (positive and negative attracted to each other) and the spacing between the nucleus and its orbiting electrons is energy dependant e.g. an electron close to the nucleus will require a lot of energy to remove it (stronger force of attraction) relative to an electron a long way from the nucleus (weaker force of attraction). (4) By splitting the atom nucleus with a fast moving neutron you release some of the energy that held it together and form two new nuclei (two new elements) (5) A large atom, with large numbers of protons and electrons (e.g. Plutonium has a nucleus containing 94 protons) if split by a neutron, will release more energy than a small atom. (6) The energy released being proportional to the mass and the speed of light squared. (7) On splitting the atom, neutrons will be released that move on to split other atoms (8) In a nuclear reactor the fission process is moderated by the use of graphite, the graphite absorbs neutrons and thereby limits the fission process. If sufficient graphite rods are inserted into a reactor they will absorb all neutrons and terminate the fission process. Conversely, if the reactor core is not moderated, the rate of fission increases exponentially to the point where it can no longer be moderated and you get Chernobyl. Figures! It takes somebody from Australia to explain what nobody else here could try to do without mentioning "Mommy", "Daddy", "shit" or "fuck". He probably also didn't mug his teacher back in grade school. Technically wrong though. Graphite helps neutrons be in the correct energy level but does not absorb neutrons. Adding more graphite to a pile increases available neutron flux and drives the reaction forward. |
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Quoted: Graphite helps neutrons be in the correct energy level but does not absorb neutrons. View Quote Since we're talking about fission chain reactions and not just fission, this point is important. Uranium has two main isotopes in nature, U235 and U238. U238 is over 99% of natural uranium. U238 tends to capture free neutrons that are zipping by. It has a "capture resonance" at the energy level that most neutron particles would be traveling at. U238 can be fissioned, if the neutrons are at a high energy, but that energy level is not possible from fission, so a chain reaction is not possible in U238. However, if you slow the neutrons down to a slower speed, they're less likely to be captured by the U238, and may encounter a U235. That's when the magic happens... because if you add a neutron to U235, fission almost always happens. You slow down neutrons by using a neutron moderator - some element or substance that the neutrons can bounce off of, and around in, to absorb their energy but that won't absorb the particles. Carbon is one such element, deuterium in heavy water is another. Enrico Fermi joked that fission was discovered because he worked in Italy, and not in the US. One of the key steps in the discovery of fission was that the effect of neutrons on Uranium was significantly different if the experiment was performed on a marble top table vs a wood table. Wood is a neutron moderator, marble is not. Fermi noted that if he'd worked in the US, everything would have been done on a wood table so there would not have been a difference to notice. You get a fission chain reaction when a neutron from one fissioning atom hits another atom and causes fission, and so on and so on. Of course the fission chain reaction gets a lot easier if you increase the percentage of U235 in the uranium - enrichment. If you increase the enrichment percentage high enough, you don't need the neutron moderator anymore as there is no U238 with its capture resonance. You can put a bunch of U235 together and it'll fission chain-react all by itself, a fast reactor. If you force a larger quantity of U235 together fast enough, it'll go through generations of chain reactions in millionths of a second, or what the Japanese call pika-don. |
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Quoted: Since we're talking about fission chain reactions and not just fission, this point is important. Uranium has two main isotopes in nature, U235 and U238. U238 is over 99% of natural uranium. U238 tends to capture free neutrons that are zipping by. It has a "capture resonance" at the energy level that most neutron particles would be traveling at. U238 can be fissioned, if the neutrons are at a high energy, but that energy level is not possible from fission, so a chain reaction is not possible in U238. However, if you slow the neutrons down to a slower speed, they're less likely to be captured by the U238, and may encounter a U235. That's when the magic happens... because if you add a neutron to U235, fission almost always happens. You slow down neutrons by using a neutron moderator - some element or substance that the neutrons can bounce off of, and around in, to absorb their energy but that won't absorb the particles. Carbon is one such element, deuterium in heavy water is another. Enrico Fermi joked that fission was discovered because he worked in Italy, and not in the US. One of the key steps in the discovery of fission was that the effect of neutrons on Uranium was significantly different if the experiment was performed on a marble top table vs a wood table. Wood is a neutron moderator, marble is not. Fermi noted that if he'd worked in the US, everything would have been done on a wood table so there would not have been a difference to notice. Of course the fission chain reaction gets a lot easier if you increase the percentage of U235 in the uranium - enrichment. If you increase the enrichment percentage high enough, you don't need the neutron moderator anymore as there is no U238 with its capture resonance. You can put a bunch of U235 together and it'll fission all by itself, a fast reactor. If you force a larger quantity of U235 together fast enough, it'll go through generations of chain reactions in millionths of a second, or what the Japanese call pika-don. View Quote Just plain ol "light" water is a great moderator as well. That's why we went "cheap" in US by using light water while our northern neighbors went with expensive heavy water. The resonance phenomenon you describe has a graph on page two of the thread (just saying for those that may not make the connection.) Finally, all anyone really needs to know. Keff = E Lf p Lth f n |
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Ironically, Germany never got the bomb because of geography. Their coal had to much boron impurity, so they had to use heavy water, which came from Norway. That's a fascinating side bit to WWII and The Heavy Water War is a great watch.
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Quoted: Since we're talking about fission chain reactions and not just fission, this point is important. Uranium has two main isotopes in nature, U235 and U238. U238 is over 99% of natural uranium. U238 tends to capture free neutrons that are zipping by. It has a "capture resonance" at the energy level that most neutron particles would be traveling at. U238 can be fissioned, if the neutrons are at a high energy, but that energy level is not possible from fission, so a chain reaction is not possible in U238. However, if you slow the neutrons down to a slower speed, they're less likely to be captured by the U238, and may encounter a U235. That's when the magic happens... because if you add a neutron to U235, fission almost always happens. You slow down neutrons by using a neutron moderator - some element or substance that the neutrons can bounce off of, and around in, to absorb their energy but that won't absorb the particles. Carbon is one such element, deuterium in heavy water is another. Enrico Fermi joked that fission was discovered because he worked in Italy, and not in the US. One of the key steps in the discovery of fission was that the effect of neutrons on Uranium was significantly different if the experiment was performed on a marble top table vs a wood table. Wood is a neutron moderator, marble is not. Fermi noted that if he'd worked in the US, everything would have been done on a wood table so there would not have been a difference to notice. Of course the fission chain reaction gets a lot easier if you increase the percentage of U235 in the uranium - enrichment. If you increase the enrichment percentage high enough, you don't need the neutron moderator anymore as there is no U238 with its capture resonance. You can put a bunch of U235 together and it'll fission all by itself, a fast reactor. If you force a larger quantity of U235 together fast enough, it'll go through generations of chain reactions in millionths of a second, or what the Japanese call pika-don. View Quote His username checks out. I'm getting a headache. But thanks for that. |
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Quoted: Figures! It takes somebody from Australia to explain what nobody else here could try to do without mentioning "Mommy", "Daddy", "shit" or "fuck". He probably also didn't mug his teacher back in grade school. View Quote View All Quotes View All Quotes Quoted: Quoted: Crudely speaking (1) An atom consists of a nucleus comprising protons and neutrons surrounded by a sea of electrons (2) A proton has a positive charge, an electron has a negative charge and a neutron is neutral (3) A stable atom is in effect balanced with respect to protons and electrons (positive and negative attracted to each other) and the spacing between the nucleus and its orbiting electrons is energy dependant e.g. an electron close to the nucleus will require a lot of energy to remove it (stronger force of attraction) relative to an electron a long way from the nucleus (weaker force of attraction). (4) By splitting the atom nucleus with a fast moving neutron you release some of the energy that held it together and form two new nuclei (two new elements) (5) A large atom, with large numbers of protons and electrons (e.g. Plutonium has a nucleus containing 94 protons) if split by a neutron, will release more energy than a small atom. (6) The energy released being proportional to the mass and the speed of light squared. (7) On splitting the atom, neutrons will be released that move on to split other atoms (8) In a nuclear reactor the fission process is moderated by the use of graphite, the graphite absorbs neutrons and thereby limits the fission process. If sufficient graphite rods are inserted into a reactor they will absorb all neutrons and terminate the fission process. Conversely, if the reactor core is not moderated, the rate of fission increases exponentially to the point where it can no longer be moderated and you get Chernobyl. Figures! It takes somebody from Australia to explain what nobody else here could try to do without mentioning "Mommy", "Daddy", "shit" or "fuck". He probably also didn't mug his teacher back in grade school. Reactors can use graphite to moderate neutrons. Reactors can also use light water or heavy water to moderate neutrons. Most reactors currently operating are moderated by light water, followed by graphite, followed by heavy water. Moderation means to slow neutrons down to a speed where their chance of absorption into the nucleus of the nuclear fuel is greatly increased. A slow moving neutron is more easily absorbed than a fast moving neutron and this neutron makes the nuclear fuel atom unstable. The unstable nuclear fuel atom splits and releasing energy and enough neutrons to start a chain reaction if the reactor is properly designed. Moderators must not absorb many neutrons or they would bring the chain reaction to a halt. Control rods are made from materials that absorb neutrons. They aren't made from graphite which moderates neutrons. Control rods control the rate of reaction in the reactor by absorbing enough neutrons to maintain the desired heat production level. So that post turned everything about how a reactor really works upside and backwards and you fell for it, hook, line, and sinker. |
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Quoted: Just plain ol "light" water is a great moderator as well. View Quote View All Quotes View All Quotes "Light" water is a moderator, but it absorbs too many neutrons to be able to maintain a chain reaction with natural uranium. You have to use enriched uranium to sustain a chain reaction with plain water as a moderator. IIRC you need like 2% U235 depending on the exact geometry etc. Graphite or heavy water, both at very high purity are IIRC the only moderators that have been successful with natural uranium. That's why we went "cheap" in US by using light water while our northern neighbors went with expensive heavy water. Someone earlier in the thread I think mentioned the CANDU reactors that use heavy water, which is because they're designed to be able to use unenriched (natural) uranium. If you can run on natural uranium you don't need enrichment capability, which makes the industrial base needed significantly easier. We had enrichment, Canada didn't. With no enrichment capability (or plutonium separation) you can't make a nuclear weapon either, so it's safer to give nuclear power technology to non-nuclear weapon countries if enrichment isn't required. If you have the capability to do enrichment, you can run it as long as you want to get to whatever percentage you want. |
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Quoted: "Light" water is a moderator, but it absorbs too many neutrons to be able to maintain a chain reaction with natural uranium. You have to use enriched uranium to sustain a chain reaction with plain water as a moderator. IIRC you need like 2% U235 depending on the exact geometry etc. Graphite or heavy water, both at very high purity are IIRC the only moderators that have been successful with natural uranium. Someone earlier in the thread I think mentioned the CANDU reactors that use heavy water, which is because they're designed to be able to use unenriched (natural) uranium. If you can run on natural uranium you don't need enrichment capability, which makes the industrial base needed significantly easier. We had enrichment, Canada didn't. With no enrichment capability (or plutonium separation) you can't make a nuclear weapon either, so it's safer to give nuclear power technology to non-nuclear weapon countries if enrichment isn't required. If you have the capability to do enrichment, you can run it as long as you want to get to whatever percentage you want. View Quote Oh, well, yeah. Sorry I missed that you were making a point about natural uranium. |
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Quoted: "Light" water is a moderator, but it absorbs too many neutrons to be able to maintain a chain reaction with natural uranium. You have to use enriched uranium to sustain a chain reaction with plain water as a moderator. IIRC you need like 2% U235 depending on the exact geometry etc. Graphite or heavy water, both at very high purity are IIRC the only moderators that have been successful with natural uranium. Someone earlier in the thread I think mentioned the CANDU reactors that use heavy water, which is because they're designed to be able to use unenriched (natural) uranium. If you can run on natural uranium you don't need enrichment capability, which makes the industrial base needed significantly easier. We had enrichment, Canada didn't. With no enrichment capability (or plutonium separation) you can't make a nuclear weapon either, so it's safer to give nuclear power technology to non-nuclear weapon countries if enrichment isn't required. If you have the capability to do enrichment, you can run it as long as you want to get to whatever percentage you want. View Quote |
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