Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Question about becquerel of nuclear waste over time

  1. Apr 28, 2016 #1
    This is a question about average light water reactors. I was wondering when the total becquerels of a spent fuel rod would equal the becquerels of that same fuel rod before it was used.
  2. jcsd
  3. Apr 28, 2016 #2

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    Note: The "Becquerel" is a unit ... you want to ask a question about "radioactivity".

    Light water reactors use U235 enriched to 3% ... it's not very radioactive.
    Spent fuel rods are mostly U238, with a little of the U235 left - and Pu.
    Back of envelope - it would be the time for almost all the Pu to decay: roughly: 400,000yr ...
    Last edited: Apr 28, 2016
  4. Apr 30, 2016 #3
    Due to the generation of fission products, the total activity of a spent fuel rod is drastically (many orders of magnitude) higher than it was going in.

    Fuel rods and fuel pellets are safe to touch and stand directly next to, prior to putting them in the reactor.

    After 6 years in a reactor, the fuel generates lethal radiation fields and can be in the million Rad/hr range.
  5. May 1, 2016 #4
    Thank you both for your answers. Maybe what we really need are fast breed reactors to burn all the Actinides. Then mostly only short lived radioisotopes would be leftover.
    Last edited: May 1, 2016
  6. May 2, 2016 #5


    User Avatar
    Staff Emeritus
    Science Advisor

    Most fuel batches these days average about 4% for BWR fuel and 4.5-4.9% for PWR fuel, with peak enrichments in fuel rods in the active zone of 4.9% in BWR fuel and 4.95% in PWR fuel (most designs use axial blankets. BWR fuel tends to use natural enrichment, while PWR fuel uses slightly enriched UO2). Discharge burnups are around 50 to 60 GWd/tU rod average.

    Slide 3 in the cited presentation show the activity after shutdown for spent fuel, uranium ore (with decay products) and process uranium (without decay products).
    It takes about 200,000 years (~10,000 generations) for the activity of spent fuel to reach the activity level of uranium ore (with decay products), it's natural state, and many millions of years to attain the activity level of it's original state as processed uranium. Bear in mind that the oldest human engineered structures are only several thousand years old.

    There are some long-lived fission products like 99Tc (half-life 2x105 y), 129I (half-life 1.6x107y), as well as transmuted U radionuclides, e.g., 236U (half-life 2.342x107y) and 237Np (half-life 2.144x106y).
  7. Aug 9, 2016 #6
    It seems to, and pardon me if this doesn't directly answer the question, though the question seems to have been well answered already, I am more reacting to that answer, - it seems to me that the production of the radioactive waste material from nuclear reactors is a huge serious drawback to the use of nuclear power to generate electricity. I looked it up somewhere on line once as to how many reactors there are and how much waste each one produces per year and the numbers were quite staggering. Couple that with the reality that we have not yet any truly safe or clever way to store or dispose of that waste and it seems like the benefits we are deriving from the fuel cost situation are far outweighed by this huge insane mess of nuclear waste we are ending up with.

    I am wondering if anyone has any ideas to how we might speed up the decay time of nuclear waste, for one thing. or what are the chances that the material could be bounded with some other elements to create something that was stable and no longer throwing off electrons(or beta or alpha or gamma, whatever the case may be). Or why isn't there anything useful we can do with that radioactive material? Okay - while writing this I did some googling. Apparently there are people working on batteries that run off of radioactivity. but right now they are high cost and low efficiency.

    Or perhaps this is more in the realm of old fashion alchemy. But what if we could break the radioactive waste down into simpler more stable elements? Or is that completely beyond any capability we have?

    In any case it does really seem like we are in desperate need to come up with something far more clever than the nuclear power plant as a way of generating electricity.

    and this may be a stupid question. But is electricity itself the sole and only form of natural phenomena which can be made to power machines and lights and everything? Are we always going to be using it and finding ways to make it? Or is there perhaps some other force, method, thing, that we might hit upon to run machines and everything, that does what electricity does but that is somehow completely different? Or is electricity so basic and intrinsic to the physical world that it is in fact what we are stuck with forever as a mechanism for running computers and cars and radios and all the crazy things we build and use that run on electricty. I don't even know what the proper term might be. force? power? is electricity the only thing like itself in nature?
  8. Aug 9, 2016 #7
    Hi DreamRelics -- Find and read "power to save the world" by Gwyneth Cravens. She covers everything except your two last paragraphs.
  9. Aug 13, 2016 #8

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    gmax137 provides a good reference... I'll focus on scietific literacy and the last two paragraphs:
    "huge" is a comparative term, when you use it you need to say what you are comparing it to.

    ... where online? Online sources vary considerably in their reliability.

    ... when? Have you not checked since? How was the search relevant to the discussion?
    Note: these are rhetorical questions. When a scientist is reading what you wrote, these kids of questions will automatically pop up - you should be writing to a scientific audience with these questions in mind.

    That would be a personal reaction. What were "the numbers" in question? What is it about them that you find "staggering"?

    Is that the reality? How do you know? It seems that nuclear engineers think they do have clever and safe ways to store nuclear waste. Maybe these are not "truly" clever or safe, but how is that not a "no true scotsman" fallacy?

    Can you see that there is no information so far that would help anyone adress your concerns.
    Don't get me wrong, in normal conversation, this sort of opening is fine. However, one of the aims of these forums is to help people understand how to listen to and talk to scientists. It is in that spirit that I am asking these questions. It will be a useful exercize for you to rewrite your opening sections (above) to take account of the kinds of questions I have deminstrated above.

    Now you have some questions:

    Technically that is not a question, but it can be treated as one. The short answer is "no".
    Besides, the faster the decay, the more radioactive the material is.
    It seems you need to find out more about what nuclear waste is, and why it is considered dangerous.

    There is zero chance that chemical bonding will affect the nuclear processes.
    Aside: only beta decay involves electron or anti-electrons as the radiating particle.
    Gamma rays are a kind of light. Nuclear decay can result in, in principle, any combination of protons and neutrons being emitted as well, it's just that when there are more than 2 protons and 2 neutrons in one particle we call that a "daughter nucleus". Exactly two of each is common, it's called an alpha particle.

    There are useful things that can be done with nuclear waste. The americium used in smoke detectors are a form of nuclear waste for example. Plutonium, which is a byproduct of Uranium reactors, is used to generate more power in plutonium reactors.

    No. That is what is happening naturally in radioactive decay - the unstable element is turning, by stages, into a more stable element. It is technically possible to turn a waste product into another radioactive substance which decays faster but there is no "magic" path to go "zap" you're safe. Besides, the stable end product of most radioactive waste decay is lead, which has it's own issues.

    That would be nice. As it happens, we have a lot of alternatives to nuclear power, each with their own issues.
    When assessing a particular solution, it is a good idea to compare it with the others. There are no perfect choices.

    No it isn't. There was a time when electricity was not used at all for energy ... wind and water power was used directly to drive machines (along with animal strength), and fire was used for heat and light. However, the modern world depends on electricity.

    Yes. That would be a reasonable projection into the future from present knowledge.Even if some previously unknown power source were discovered, there will still be some use in using electricity just like we still use water wheels, animals, gas etc directly to do some things. ie. people still use horses for transport in someplaces.

    It is unlikely that there would be a hitherto unknown and unsuspected physical process that would also be a plug-in replacement for electricity. To work as electricity does, it would have to be electricity.

    Electricity is a branch of applied electromagnetism. Electromagnetism is a fundamental force of Nature. However, there arelots of other ways to run cars and computers and such stuff - we currently build a lot of stuff out of electrical components because that's cheap and convenient to do but we don't have to. ie. we don't need to build observatories using cctv optics: in the past we used ground glass and metal or wood and before that we used great huge slabs of rock. It is possible to make a gravity driven computer out of ramps and balls.

    I don't know what you mean by that. What would something need to be able to do to be "like electricity" in the sense you mean?
    If it were exactly like electricity, then it would be electricity. Analogues of electric circuits can be made out of pipes carrying water or gas - does that count?

    A lot of this has been more pedantic than I am normally wont to be. I don't normally bother. However, in your case you seem to care about what is true and how you can sort out different ideas and the scientific questioning habit I tried to illustrate at the top of this post will help you with that. In the second part. It will certainly help you refine the questions in the last few paragraphs into something you can better investigate.
  10. Aug 15, 2016 #9
    Thank you very much Simon for that thoughtful reply. You are correct on all points. It was some time ago when I was reading the information about nuclear waste production and storage and I certainly do not remember the figures at this point. Looking now I find this number.

    "A typical nuclear power plant in a year generates 20 metric tons of used nuclear fuel. The nuclear industry generates a total of about 2,000 - 2,300 metric tons of used fuel per year.

    Over the past four decades, the entire industry has produced 76,430 metric tons of used nuclear fuel. If used fuel assemblies were stacked end-to-end and side-by-side, this would cover a football field about eight yards deep."

    also looking now I find this information. Apparently there was a containment issue with storage facility in New Mexico some time back. A proposed site in the Yucca mountains has been sidelined by the Obama admin. Thus. "This leaves US non-governmental entities, such as utilities, without any designated long term storage site for the high level radioactive waste stored on-site at various nuclear facilities around the country. The US government disposes of its waste at WIPP in New Mexico, in rooms 2,150 feet (660 m) underground.[4] The Department of Energy (DOE) is reviewing other options for a high-level waste repository and the Blue Ribbon Commission on America's Nuclear Future, established by the Secretary of Energy, released its final report in January 2012. It expressed urgency to find a consolidated, geological repository, and that any future facility should be developed by a new independent organization with direct access to the Nuclear Waste Fund, that is not subject to political and financial control like the DOE.[5] In the meantime, most nuclear power plants in the United States have resorted to the indefinite on-site dry cask storage of waste in nearly impervious steel and concrete casks."

    Anyway, the system as it is seems a bit haphazard. Also, apparently thanks to Carter the USA does not reprocess our fuel which is wasteful and idiotic. It would seem. Though i get what the point was about nuclear bomb proliferation that tactic seems more naive than effective.

    As to the point about speeding up the decay or rendering it into something more stable. Right I know it all turns into lead eventually. I suppose we might assume that all the lead on our planet is the remnants of radioactive materials from long ago. But as I understand it, each of the successive elements is made by the bonding together of the lighter ones in the sun. All the subatomic bits get fitted together by that process. So I wonder if uranium or plutonium or whatever the atomic waste is, since its problem is that the atoms are unstable I am envisioning a process where an unstable heavy element can be brought together with the right lighter element and create a fusion that sucks off the radioactive bits and makes the lighter element into one up the chain a little ways. After all, are not all the elements just sort of like puzzle pieces of the more basic elements joined together? Doesn't the instability create a sort of opening into which we might be able to add the necessary bits to make the element stable or something like that? Anyway that is the idea. Poorly articulated though it may be.

    as to the point about electricity. All the other examples you mention of things that accomplish work are more primitive. What I was getting at is whether or not there was another fundamental force like electricity that could run through wires, power lights, generate heat, like basically be the basis for higher technology the same way that we use electricity. But i am guessing the answer is no. I suppose it is a silly question and one that verges on fantastic science fiction kinds of notions, it is just that at the moment when the question occurred to me I was really struck by the realization of how basic and unique electricity is. I suppose the fact that it works the way it does is because everything has electrons in it.
  11. Aug 15, 2016 #10

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    Your source for the first part appears to be wikipedia - do not forget to cite sources.
    Is 20T of used fuel per plant a big number? Did you compare it to anything?
    Have you had a look at the source recommended to you?

    Technically all elements besides hydrogen is the byproduct of nuclear processes occurring long ago. I don't know that it is generally held that all the lead on the Earth comes from nuclear decay from after the formationof the Earth. However, for eg, about half the Uranium at the formation of the earth would be lead now.

    The general rule is that the heavier the element, the more unstable it is. To make a lump of plutonium more stable you have to break it apart. You could, technically, force it to fission into a bunch of helium and hydrogen atoms and that would be stable. However, the energy needed to make that happen is bigger than what you'd get from the original process that made the plutonium.

    Fortunately, in the case of putonium, you can use it in fission reactors to make more energy ... and then deal with the daughter nuclei from that.
    The biggest problem with nuclear waste is usually that it is highly toxic, not that it is radioactive.

    ... sort of. But like any puzzle, you have to obey the rules when you fit the bits together or take them apart. You need a physical process to achieve the results. It takes time and energy to make stuff happen.

    No. Nothing like that.

    Define "primitive"? Electricity is a fundamental process, more fundamental than, say, a horse walking and pulling something.
    What we do in a nuclear power plant is use the heat from the fission to boil water, to drive a steam engine. It is the same with coal plants - the difference is what we use to make the heat. We could just use big mirrors to direct sunlight onto a water tank and so use the Sun to boil the water ... would that be more or less primitive? Mirrors are high tech, the Sun is a nuclear fusion reactor... but it's still a steam engine and we've been using those since the dawn of the industrial revolution.

    What you described is a force that is exactly like electricity ... in which case, it actually is electricity. If you have an object that looks like a duck, it acts like a duck, and is ever bit like a duck in all ways ... it's a duck. You may assert it is not, in fact, a duck - but if there is no way to tell the difference between it and a duck, it's a duck. This is a basic principle that saves a lot of effort.

    Maybe there is something that we do not know about. Then, all we can say about that is that we do not know about it.

    Right now we know of four distinguishable forces (electricity is not a force btw, it is the label given a group of phenomena) - these are electromagnetic, gravitational, strong nuclear and weak nuclear forces.
    Electromagnetism is the force responsible for almost everything you see around you - it is the basis of chemistry, and electricity and magnetism.
    We have learned to direct this force to do work. Directly with electricity generation and electrical machines, and indirectly ie agriculture, fire, the wheel and so forth.
    Gravity is the other main one we experience every day - we can also exploit this to do work, such as when we build a water-wheel ... although we are actually exploiting the way Nature stores electromagnetic energy from the Sun as gravitational potential energy, the Sun ultimately get's it's energy from gravity.
    Gravity is also handy for sticking stuff to the ground.

    The strong nuclear force is responsible for holding atomic nucleus together - we use it for energy in nuclear reactors, though, unlike electricity or gravity it is harder to use it directly since it mostly makes heat. But we can turn that heat directly into mechanical kinetic energy by heating a fluid ... thus: steam engine.
    Nuclear batteries use the heat from nuclear decay to drive a stirling engine or a thermo-electric transducer.

    The weak nuclear force is responsible for beta decay and some other stuff ... I don't think we have any way to use the force for energy useful for doing work.
    Maybe someone will some day ... but it won't be like electricity since it operates quite differently.

    That's basically it for forces. There is currently no reason to believe there may be any other forces and some reason to believe that these four are actually different aspects of a single super-force as yet unobserved.

    That should help your thinking somewhat.
  12. Aug 15, 2016 #11
    hmm' I don't know that I have come across anyone asserting that gravity was part of the electromagnetic force/phenomenon. I though gravity was something that we still don't have a great deal of insight into exactly what it is or what causes it. Lots of data on what it does. and I guess curved space time is one explanation of sorts about gravity. But I was under the impression that there were still many mysteries to it.

    Electromagnetism is very interesting. As I understand it, they are related, but they do have some differences that are not fully explained. Electricity creates magnetic fields, and magnets can create electricity. but they don't have all the same properties as each other. For instance there is no such thing as a monopole magnet.
    I always wished I had a ton of money to build weird things with magnets. Magnetism is cool. One thing I wondered about. I read that at least with manufactured magnets that high temperatures can cause them to loose their magnetism. If that is so, I never quite understood how the molten dynamo of the earth's core could be generating the earth's magnetic field.

    It does rather seem like the four basic forces and maybe many of the larger observed phenomenon must have influences and interactions and causes that are at the quantum level. All those vibrating strings and so forth.
  13. Aug 15, 2016 #12

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    I find that unlikely ... it is basic High School text book stuff. See also:

    Define "insight". We have as much understanding of gravity as we do any fundamental force. Though you should know that we do not strictly have a cause for any fundamental force - that's why it is fundamental. But if charges and charge density can be thought of as the cause of electromagnetic force then mass and energy density is equally the cause of gravitational interactions. What else did you have in mind?

    There are still many mysteries to physics as a whole but we know a lot about gravity.

    Nothing is "fully explained", but we do know more than you seem to think.
    Electricity and magnetism are each an aspect of the same underlying thing.

    Irrelevant - heads and tails don't have all the same properties as each other either but they are both part of the same coin. The unification of electricity and magnetism is an established fact of physics established in print by Faraday and Maxwel. Since them there have been confirmation in the relativistic and quantum mechanical pictures.

    Where? Honestly, are you paying attention to what I tell you? Use citations.
    The clue is in the name: "dynamo". Dynamo's work at any temperature while solid permanent magnets can lose their magnetism when their magnetic domains go into disarray, ie when they get shaken up too much.
    See also:

    "Fundamental" not "basic" ... and it's the other way around: the classica forces do not "have influences and interactions and causes that are at the quantum level", rather, the classical forces are an emergent phenomenon of the underlying QM interactions. At the quantum level the idea of causation gets tricky, see also:

    String Theory is a whole other kettle of piranhas. You are having enough trouble dealing with the idea of the fundamental forces. Try just sticking to the standard model.
  14. Aug 15, 2016 #13

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    We are well off the original point now ... you have a lot of catching up to do.
    Do read the references provided. Good luck in your studies.
  15. Aug 15, 2016 #14
    Thanks. I will read those links. Most of what I have been exposed to on these topics has come from reading Asimov's History of physics. New Intelligent man's guide to science and Nigel calder's book Einstein's Universe as well as some book by michio kaku, the title of which I do not recall. And looking up things online. Oh and the book the holographic universe. But not much in the way of formal classes. Well none. And somehow I missed all this stuff in high school, though, at that time in my life I had no interest in science at all. All I studied in college was art. Never got past trig in high school and none of that made the least bot of sense to me at the time. But for some reason I find physics very interesting. So I am interested in deepening my understanding of it. So thanks. I remember lots of the bits of all that stuff I have read but perhaps in a somewhat vague and incomplete way. and I am given toward wild imaginings.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted