Score
Title
9418
Megathread: 2017 Hurricane Season
24
Earthquake Megathread
6172
If a nuclear bomb went off in Boston harbor could scientists tell after the fact who had manufactured it, do they leave distinct radioactive signatures?
5747
Why aren't there any orbitals after s, p, d and f?
16
What do sexes in fungus mean?
135
Do black holes have electromagnetic field?
4
Where does the "blast" portion of a nuclear explosion come from?
6
Do atmospheric CO2 measurements include a significant diurnal cycle?
8
How do bionic arms work?
4
Historically, when large numbers of sailboats/ships had to travel in formation as a fleet, are there different dynamics governing the movement of ships in the front, middle and rear of the group?
6
Why are non-differentiable continuous functions integrable?
9
Are Toucans (Americas) and Hornbills (Asia/Africa) an example of convergent evolution?
4
What are the estimated thicknesses for northern sea-ice at the height of the Pleistocene glaciation, and how are those thicknesses estimated?
7
Ask Anything Wednesday - Physics, Astronomy, Earth and Planetary Science
2
Why are rainbows in an arc shape and does the radius change?
4
Why do nuclei release energy when they fuse?
24
How many layers are there in a modern integrated circuit?
8
Why does the Earth's rotation effect Rockets and not Planes?
2
Are there plant/animal somatic hybrids?
2
Would the opposite of codependency issues be considered as unhealthy as codependency? Wherein any form of dependency is abhorrent to the person in question? Does this have a clinical classification?
60
Do people that have degenerative diseases such as Alzheimer's lose their muscle memory as well?
20
How is it possible that something as large as a possible Planet 9 has completely evaded visual observation?
8154
There is a video on the Front Page about the Navy's Railgun being developed. What kind of energy, damage would these sort of rounds do?
8
Would global cooling create more land? If so, how much more land would be available before the whole earth freezes?
11
How did they measure hurricane wind speeds in the 1800's?
4125
In 1972 a woman fell 33,332 feet without dying. How is that possible?
12
How is it that scissors can curl ribbons?
12
What is happening at a molecular level when a knife cuts through nylon rope?
154
Could we railgun the Moon?
15
Why is caesium the largest atom? Shouldn't element 118 be the largest?
1
Why does your metabolism slow down with age?
7
Do snakes that can 'see' heat, such as ball pythons, compare their 'heat vision' with their normal vision?
17
[CHEMISTRY] How do chemical companies determine if one ingredient in a solution can be replaced by another?
2
In emergencies like on CDMX will using cellphone data on a very far state affect the capacity on CDMX cell towers to make calls and/or use cell phone data?
12
Can a human be allergic to any substance? As in, does every material have the potential to elicit an allergic response?
2
What defines an equation of state?
46
How is online gaming possible if there must be some delay?
5
Does my peripheral vision have a different latency than objects I look directly at?
15
Why is gold found in seams?
16
On an alien planet, would a regular compass still point true north?
11
Can someone with reading Aphasia "read" in Braille?
4
Would negative kelvin body always transfer heat to positive kelvin body?
2656 RobusEtCeleritas We can't force nuclei to decay, but we can make them undergo reactions that turn them into other nuclei which decay faster. There is some promise of doing this with waste from nuclear reactors, so that we don't have to store it as long.
233 mfb- Uranium is not the problematic part of nuclear waste. The problematic part comes from elements that are produced during reactor operation, either as fission products or as uranium nuclei that caught neutrons and then decayed to other elements.
28 spinur1848 Others have already said we can't influence the rate of decay, and this is true. The decay rate is an intrinsic property of any given nucleus. But that wasn't really your question. You asked why we can't keep decaying the uranium until it isn't radioactive anymore. The answer is that we can, but it takes a bit more than just leaving the fuel in the reactor. The stuff that goes into the reactor has uranium in it, but it isn't pure uranium; most of it is U238, which isn't very radioactive at all. Theres also other stuff in and around the fuel like the moderator made out of heavy water or graphite that slows neutrons down. In order to start and sustain a fission reaction, you need a high enough density of neutrons with just the right energy level to split another nucleus and generate more neutrons. We get that by carefully balancing how many neutrons get produced with how many neutrons get absorbed. With fresh fuel thus is straight forward. As it reacts it builds up all sorts of other decay products that absorb neutrons and poison the reaction. These decay products are still very radioactive, they just don't produce the right kind of neutrons. So if you want to keep reacting the uranium you need to reprocess the fuel to get rid of the waste products. It turns out that this is extremely expensive and dangerous to do. So much so that most folks just mine fresh uranium out of the ground instead. Unless you have other uses for the waste, like bombs. Most sane folks don't want more nuclear bombs around than there already are, and the kind of buildings and machinery you would use to reprocess fuel for power are exactly the same ones you would use to build bombs (this is what is meant by dual use technology). So if you don't want anyone to have a legitimate reason to have that kind of equipment lying around, you make sure the world price of uranium is just low enough to ensure it's easier to get new fuel instead of reprocessing the old fuel.
56 BCJ_Eng_Consulting So what you can do with fission products is "transmute" them with neutron bombardments. There are complexities to it that make it difficult in practice. In principle, what you can do is bombard the radiactive waste with neutrons, this makes the nucleus MORE unstable so that it is more radioactive. It then decays and now you have a stable daughter product. As an example, say we have strontium-90 with a troublesome 28 year half life. Well, if you hit it with a neutron, it become strontium-91 with a 9.5 hour half life, which becomes yttrium-91 with a 58.5 day half life, which becomes stable zirconium-91. This would shorten how long you have to look after the waste. Same thing for Cesium-137 with a 30 year half life. If you get it to absorb a neutron, it becomes cesium-138 which has a half life of 32 minutes and becomes stable barium-138. Both of those examples have to do with some pretty "bad actors" as it comes to rad waste storage in the first few hundred years. The longer term decay products that are millions of years half life are generally transuranics and can be fissioned to become shorter lived fission products so they go from millions of years to tens of years (I'm simplifying a bit here). The issue with this is a lot of fission products don't have large neutron capture cross sections. Even then, if you did irradiate them, not all of them would absorb a neutron. Some of them would absorb multiple neutrons and may turn into a more problematic nuclide than you started with (say, already stable fission products that you just now made radioactive through neutron activation). You also have a hard time treating the original spent fuel to separate out the specific species you want to transmute. I believe some folks have advocated accelerator driven transmutation as a possible source to break rad waste down more quickly it's largely plagued with the same issues as neutron bombardment. The bottom line is, we don't actually have that much spent nuclear fuel, concrete casks are relatively cheap, pretty effective, and the longer you wait, the easier it generally is to recycle/reprocess the spent fuel.
79 IronBear76 Are actually asking "Why don't we just fission all the uranium until there is no more?" The reason why this does not work is that the results of nuclear fission result in things that are radioactive. Additionally the chain reaction that is used to fission uranium is not flawless. Neutrons are easily absorbed by impurities in the uranium and sometimes the uranium itself. So as more and more of the uranium turns into other byproducts, there are more atoms around to absorb the free neutrons. So that is why we can't just fission away all the radioactive materials on the earth. Most are unfissionable and the growing byproducts of uranium make it harder and harder for chain reaction to keep going.
10 Dorito23 That's kinda what we're doing. Nuclear plant worker here. When the fission process slows down enough to where it isn't producing the heat required to make sufficient power the rod bundle is removed from the reactor during an outage. When it comes out it is under water and stays there because it is still highly radioactive. They place the rod bundles in a cooling pool where it will sit for around the next 20 years. Until it is cool enough and stable and safe enough to remove. Then it goes into those concrete coffins where it sits for the rest of its life until the world finds a decent way of truly disposing of it.
7 AcetylcholineAgonist I think this is a conceptual issue. The way you're starting the issue makes it sound like you think we control the fission reaction. We don't. There reaction happens according to probability, and we have nothing to do with it. It happens in the deposits of material still in the ground, it happens in the waste stockpiles, it happens wherever an isotope exists. What we do in nuclear power it's harness the energy that nature provides.
6 ifiwereabravo There is no way to know how long it will take for someone somewhere to invent something as revolutionary as a rapid radiation decay process. But if your interested in the subject look into learning more about college level physics. There are lots of fascinating things to know there.
2654 0 RobusEtCeleritas We can't force nuclei to decay, but we can make them undergo reactions that turn them into other nuclei which decay faster. There is some promise of doing this with waste from nuclear reactors, so that we don't have to store it as long.
231 0 mfb- Uranium is not the problematic part of nuclear waste. The problematic part comes from elements that are produced during reactor operation, either as fission products or as uranium nuclei that caught neutrons and then decayed to other elements.
29 0 spinur1848 Others have already said we can't influence the rate of decay, and this is true. The decay rate is an intrinsic property of any given nucleus. But that wasn't really your question. You asked why we can't keep decaying the uranium until it isn't radioactive anymore. The answer is that we can, but it takes a bit more than just leaving the fuel in the reactor. The stuff that goes into the reactor has uranium in it, but it isn't pure uranium; most of it is U238, which isn't very radioactive at all. Theres also other stuff in and around the fuel like the moderator made out of heavy water or graphite that slows neutrons down. In order to start and sustain a fission reaction, you need a high enough density of neutrons with just the right energy level to split another nucleus and generate more neutrons. We get that by carefully balancing how many neutrons get produced with how many neutrons get absorbed. With fresh fuel thus is straight forward. As it reacts it builds up all sorts of other decay products that absorb neutrons and poison the reaction. These decay products are still very radioactive, they just don't produce the right kind of neutrons. So if you want to keep reacting the uranium you need to reprocess the fuel to get rid of the waste products. It turns out that this is extremely expensive and dangerous to do. So much so that most folks just mine fresh uranium out of the ground instead. Unless you have other uses for the waste, like bombs. Most sane folks don't want more nuclear bombs around than there already are, and the kind of buildings and machinery you would use to reprocess fuel for power are exactly the same ones you would use to build bombs (this is what is meant by dual use technology). So if you don't want anyone to have a legitimate reason to have that kind of equipment lying around, you make sure the world price of uranium is just low enough to ensure it's easier to get new fuel instead of reprocessing the old fuel.
56 0 BCJ_Eng_Consulting So what you can do with fission products is "transmute" them with neutron bombardments. There are complexities to it that make it difficult in practice. In principle, what you can do is bombard the radiactive waste with neutrons, this makes the nucleus MORE unstable so that it is more radioactive. It then decays and now you have a stable daughter product. As an example, say we have strontium-90 with a troublesome 28 year half life. Well, if you hit it with a neutron, it become strontium-91 with a 9.5 hour half life, which becomes yttrium-91 with a 58.5 day half life, which becomes stable zirconium-91. This would shorten how long you have to look after the waste. Same thing for Cesium-137 with a 30 year half life. If you get it to absorb a neutron, it becomes cesium-138 which has a half life of 32 minutes and becomes stable barium-138. Both of those examples have to do with some pretty "bad actors" as it comes to rad waste storage in the first few hundred years. The longer term decay products that are millions of years half life are generally transuranics and can be fissioned to become shorter lived fission products so they go from millions of years to tens of years (I'm simplifying a bit here). The issue with this is a lot of fission products don't have large neutron capture cross sections. Even then, if you did irradiate them, not all of them would absorb a neutron. Some of them would absorb multiple neutrons and may turn into a more problematic nuclide than you started with (say, already stable fission products that you just now made radioactive through neutron activation). You also have a hard time treating the original spent fuel to separate out the specific species you want to transmute. I believe some folks have advocated accelerator driven transmutation as a possible source to break rad waste down more quickly it's largely plagued with the same issues as neutron bombardment. The bottom line is, we don't actually have that much spent nuclear fuel, concrete casks are relatively cheap, pretty effective, and the longer you wait, the easier it generally is to recycle/reprocess the spent fuel.
84 0 IronBear76 Are actually asking "Why don't we just fission all the uranium until there is no more?" The reason why this does not work is that the results of nuclear fission result in things that are radioactive. Additionally the chain reaction that is used to fission uranium is not flawless. Neutrons are easily absorbed by impurities in the uranium and sometimes the uranium itself. So as more and more of the uranium turns into other byproducts, there are more atoms around to absorb the free neutrons. So that is why we can't just fission away all the radioactive materials on the earth. Most are unfissionable and the growing byproducts of uranium make it harder and harder for chain reaction to keep going.
12 0 Dorito23 That's kinda what we're doing. Nuclear plant worker here. When the fission process slows down enough to where it isn't producing the heat required to make sufficient power the rod bundle is removed from the reactor during an outage. When it comes out it is under water and stays there because it is still highly radioactive. They place the rod bundles in a cooling pool where it will sit for around the next 20 years. Until it is cool enough and stable and safe enough to remove. Then it goes into those concrete coffins where it sits for the rest of its life until the world finds a decent way of truly disposing of it.
7 0 AcetylcholineAgonist I think this is a conceptual issue. The way you're starting the issue makes it sound like you think we control the fission reaction. We don't. There reaction happens according to probability, and we have nothing to do with it. It happens in the deposits of material still in the ground, it happens in the waste stockpiles, it happens wherever an isotope exists. What we do in nuclear power it's harness the energy that nature provides.
6 0 ifiwereabravo There is no way to know how long it will take for someone somewhere to invent something as revolutionary as a rapid radiation decay process. But if your interested in the subject look into learning more about college level physics. There are lots of fascinating things to know there.