Nuclear Energy - I need to vent/rant

[Schneibster]

OK, first things first. I screwed up, and forgot the transuranics that are present in spent single-cycle fuel. There are three classes of radioactive isotopes present in single-cycle spent fuel, more or less:
1. High-activity short half-life radioisotopes of relatively light elements like cesium, strontium, and so forth. The longest lived of these is samarium-151, with a half-life of 90 years. These are an extreme short-term danger because of their high activity.
2. Medium-activity medium half-life radioisotopes of transuranics like plutonium-239 with a half-life of 24,100 years. These are the long-term danger in nuclear wastes, because these are also gamma emitters.
3. Low-activity long half-life radioisotopes of light elements; the shortest half-life among these is technetium-99, with a half-life of 211,000 years. These are low-activity radioisotopes that don't present much danger.

If you process spent nuclear fuel made from low-enriched uranium, that is, about 5% U-235 to start with, and remove the transuranics from it, or if you burn such fuel in an integral fast reactor or some designs of pebble-bed reactors, which burn all of the transuranics, you're left with the short-term high-level and long-term low-level isotopes, but none of the medium-term medium-level isotopes that make the spent fuel hazardous long-term. Such waste is very hot in the short term, but cools down after a hundred years or so quite a bit; most of the short-term high-activity waste is gone. After 100-300 years (depending on who you believe), the activity is no greater than uranium ore. Processing to remove the transuranics, which are primarily plutonium-239, is relatively simple because they are all actinides, and therefore chemically similar. You'll also incidentally remove most if not all of the uranium, which is also an actinide. This will leave you with a small amount of waste compared to the original, composed of the short half-life and long half-life isotopes of light elements. The actinides can all be used again as fuel; the waste is disposed of (after separation of some of the light isotopes that are useful in medical research and therapy and for the manufacture of certain products).

However, I have to confess my mistake; since spent fuel in the US is not reprocessed to remove the transuranics, and since we don't use reactor designs that burn all the actinides, such waste as they produce is, indeed, dangerous for thousands of years. However, to the best of my knowledge, no such waste has ever been buried. It's still sitting in dumps at the sites of nuclear plants, since there's no other safe place to put it. The obvious solution is to wait for the integral fast reactors, or other fast neutron reactors, in which it can be burned, then reprocess it (or even just put it in as-is; designs capable of using the majority of this stuff as fuel are available) and dispose of the greatly reduced amount of waste of a lower level of hazard. And if it doesn't all get put in casks and shipped off to Yucca Mountain, that's almost certainly what we'll do. That spent fuel will then represent a resource rather than a problem. And the safety of nuclear waste will be increased (at least in the medium term, over 300 years).

This information is cribbed from the Wikipedia article on Integral Fast Reactors^WP. It is sourced from the Cal State Berkeley Nuclear Engineering department's site here.

 

[Schneibster]

That's interesting, because when I suggested that before, it was shot down. I was assured that radiation always went down. I assume though, that this is relatively short-lived? Any particularly awful daughter products will tend to disappear rather quickly? And the long-lived products will prevail?

No, you were assured that radiation from spent reactor fuel always goes down. What Buzzo is talking about is what happens in a sample of purified long half-life radioisotope, such as U-235 or U-238. Initially, there is nothing there but uranium (for example). The radioactivity is pretty low. However, as the uranium decays, daughter products are created, and these release more radiation than uranium does; some of them, as you noted, have half-lives in days or weeks. Despite extremely small quantities due to the obvious mathematics of how much of them can be present at maximum, they are very active, so they contribute a significant amount to the radioactivity of the sample; its radioactivity therefore increases for a short time, until equilibrium concentration of the short-lived isotopes occurs.

The situation is very different in spent fuel. Spent fuel has had years or decades to reach equilibrium, and in addition it contains fission products, most of which are of the short half-life high activity or long half-live low activity types I discussed in my previous post. Even with the addition of the transuranics, spent fuel is already very close to or at equilibrium, and so the radioactivity levels will not increase over time as they do in a pure sample freshly cast.

 

[Schneibster]

Apollo, I know you're more familiar with the CANDUs, but it's my understanding that the spent fuel from reactors that use natural uranium produce more plutonium than standard light-water reactors. Is that correct? What about americium?

And is the amount of plutonium in spent fuel from light-water reactors so low as to be considered trivial?

That is another point. I should have addressed it in my first post of today, but I forgot.

The spent fuel from a light water reactor has been exposed to lower energy neutrons because of the moderation techniques used in light water reactors; these lower the energy of the neutrons to what is called "thermal" levels. Such neutrons are quite good at initiating fission, but not so good at being absorbed by U-238 (which must happen for it to be transmuted to plutonium-239). The higher energy, "fast" neutrons are better at that. The concentration of plutonium in spent low-enriched fuel from a "thermal" reactor, therefore, is not high in plutonium; there is enough to make it dangerous, but the concentration is only about 1%, according to the Wikipedia article on Spent Nuclear Fuel^WP.

The majority of the long-term danger is in plutonium; but the amount of plutonium produced is only 1%. The material is far more dangerous due to the light high-level short half-life fission products, which make up several percent. Still, it's 96% U-238. And as it turns out, I was actually technically correct in my analysis; I merely underestimated the problem of the transuranics (primarily plutonium). But not by much; after 300 years at the most, and some sources say as little as 100 years, all of the high-level short half-life stuff is gone; what you're left with is low-level long half-life stuff, 96% U-238, a few percent long-lived fission products like technetium-99, and one percent transuranics. Because of the low concentration, and because natural uranium contains daughter isotopes from its radioactive decay process that make it hotter than the uranium alone, such waste is still no more active after 100 years than natural uranium; and if you'll recall, that's precisely the claim I made. I was, however, unintentionally deceptive on the following point:
By natural uranium, I meant uranium in equilibrium, not freshly cast. I didn't make this clear because I hadn't thought about the buildup of daughter nuclides at that time.

So that's the whole story, and you can look it up for yourself and follow through to the initial sources.

And it now appears that we have another alarmist in our midst. Apollo, I have to say that the practices you describe are deplorable. You should quite rightly raise hell over them. I certainly would. But you've gotten the underlying fight wrong. It's not about nuclear. It's about transparency. The problem you describe is about people hiding problems, not about the problems themselves.

Furthermore, it appears that you were incorrect regarding CANDU waste, and natural uranium waste in general; this waste has less fission products (the uranium started out with only 0.7% U-235, not 5%, so there is less of it to burn) and less plutonium (on the close order of 0.3%). It is therefore correspondingly less dangerous than single-cycle low-enriched spent fuel. The source, again, is Wikipedia, and it's the same article.

 

[Schneibster]

You might be surprised. Several of the people on this forum have no problem with spent fuel storage tanks nearby and claim that civilian nuclear waste is not hazardous after a few decades. The specific claim was that it was no more radioactive than natural uranium after 100 years and hardly more so after 30.

Actually, on this note, I should point out that this has not been substantiated, and while I haven't asked for a lot of references, this is one where I'm going to demand it, because everything I read indicates otherwise.

You've got them.

I spoke to a friend of mine yesterday, an engineer, though not a nuclear engineer. He is a former proponent of nuclear energy, now in the Green Party and a passionate opponent. He said that while he wasn't sure how to assess the claim that 100 year old spent fuel was no more dangerous than natural uranium, he suggested that I calculate the lethal dose of natural uranium.

So I've done my best. This is not my area of expertise and I appreciate corrections. But here's what I've got.

I went to this site and tried to calculate the dose for natural uranium.

http://www.wise-uranium.org/rdcu.html

I plugged in just the numbers you gave me. 22 kg bundles and 4500 of them in a loaded reactor. That gave me about 100 tonnes of natural uranium, which gives a dose of gamma radiation of 1.079 mSv/h and 468.2 Sv/h of external radiation from soil (that seemed to be the closest option given to having a stack of this stuff next to you). Meanwhile the following site gives a lethal dose as 3-5 Sv:

http://www4.tsl.uu.se/~radiation_protection/RPCOURS.htm#dlimi

So my cursory understanding says that a stack of natural uranium as large as the spent fuel from one refueling would deliver about 100 times the lethal dose of radiation in an hour. Unless there's something I've totally screwed up.

Yes, there is. How precisely do you intend to eat 100 tonnes of uranium? For that matter, how will you eat a single kilogram? Remember: uranium is an alpha emitter. Alpha particles can't get past your skin. Do you recall that conversation? That means you have to eat it. It's kind of like saying, "That snake has enough venom in it to kill ten people!!!11one!!" How precisely are ten people going to get bit by the same snake? Odds are, it might bite one, and unless it's lucky it will die right there.

Next, you misread. It's 468.2Sv/a. That's per annum; per year. Divide it by 8,760 hours. Furthermore, because you chose all that spent fuel, the calculator knows you can't get close to it, so the actual exposure turns out to be less than 2mSv/hr.

Then there's the fact that your source states a fatal dose without discussion of the time period in which that dose must be absorbed for it to cause death. That time period is short. Minutes or hours is typical.

You wouldn't want to roll around in it; but it's not going to strike you dead if you look at it for ten seconds. It won't even make you sick if you pick it up.

And finally, remember that radiation workers are limited to 50mSv/yr, and 100mSv over five years (in Canada). Levels of instant exposure of up to 200mSv in a single dose, not over a period of five years, are not known to cause any overt symptom at all; see the Wikipedia article on Radiation Poisoning^WP. There is even argument about whether they'll cause cancer or not. There are inhabited places on Earth where the background radiation is over 200mSv/yr. Everyone seems fine.

Which might well be, because the dose calculator I used gave slightly higher doses the longer the delay. So I'd appreciate some help.

Hopefully this series of posts will give you more information.

 

[Belz...]

Okay, fellows, look at this message from Schneibster way back. I didn't misrepresent what he said. A number of posts defended this position as well.

What are we looking for ?

 

[Belz...]

There are inhabited places on Earth where the background radiation is over 200mSv/yr. Everyone seems fine.

Linky ?

 

[luddite]

Yes, there is. How precisely do you intend to eat 100 tonnes of uranium? For that matter, how will you eat a single kilogram? Remember: uranium is an alpha emitter. Alpha particles can't get past your skin. Do you recall that conversation? That means you have to eat it. It's kind of like saying, "That snake has enough venom in it to kill ten people!!!11one!!" How precisely are ten people going to get bit by the same snake? Odds are, it might bite one, and unless it's lucky it will die right there.

The calculator calculates for various types of exposure. I calculated for external exposure, not ingestion. I assume it does the right thing. If I had put in exposure to 100 tonnes of uranium by ingestion, I would have gotten an even higher number, 118.8 kSv/h. And by inhalation, higher still at 19.83 MSv/h. So no, I didn't get that part wrong. Though of course these higher numbers would be relevant if the uranium contaminates the soil and water and people do start ingesting it. Obviously not 100 tonnes at a time. I didn't bother with that calculation for this reason - you have to figure out contamination rates, rates of ingestion and so on. Even though I know that in practice, contamination would affect people most by ingestion.

The source "Stack of refined uranium rods standing beside you" was not an option given for radiation source. So I chose "external radiation from soil". I assume they calculate properly for this kind of radiation. Your skin may be quite good at blocking it, but I assume some portion gets by. And apparently, that's enough to hurt you pretty badly if you've got enough natural uranium around.

Next, you misread. It's 468.2Sv/a. That's per annum; per year. Divide it by 8,760 hours. Furthermore, because you chose all that spent fuel, the calculator knows you can't get close to it, so the actual exposure turns out to be less than 2mSv/hr.

No, it's 468.2 Sv/h. The calculation per year was 4.104 MSv/a. I just checked.

Thanks for the other information. I'll look into it.

 

[luddite]

Furthermore, it appears that you were incorrect regarding CANDU waste, and natural uranium waste in general; this waste has less fission products (the uranium started out with only 0.7% U-235, not 5%, so there is less of it to burn) and less plutonium (on the close order of 0.3%). It is therefore correspondingly less dangerous than single-cycle low-enriched spent fuel. The source, again, is Wikipedia, and it's the same article.

I think the statement about CANDU waste was mine, and I just looked up the source of my misunderstanding. CANDUs produce more weapons-grade plutonium, not plutonium in general. It's a disposal issue Canadians are concerned with.

Plutonium produced in other reactors, such as graphite-moderated reactors (some of which are in operation in Britain, Russia, and elsewhere) or heavy water reactors used in Canada and elsewhere, has a composition in between that shown for weapons grade and reactor grade plutonium in the table.

http://www.ieer.org/ensec/no-3/puchange.html

The absolute amount of plutonium (or at least fissile plutonium), though, is not lower in the CANDUs:

It should also be noted that the concentrations of total fissile plutonium (plutonium 239 plus plutonium 241) are not dissimilar for these reactor types, but that PWR fuel contains relatively low concentrations of plutonium 239 and high concentrations of plutonium 241.

http://www.isis-online.org/publications/fmct/primer/Section_II_nopics.html

There's a chart at the end of the link that gives details of plutonium in reactor fuel by type of reactor.

 

[Schneibster]

The calculator calculates for various types of exposure. I calculated for external exposure, not ingestion. I assume it does the right thing. If I had put in exposure to 100 tonnes of uranium by ingestion, I would have gotten an even higher number, 118.8 kSv/h. And by inhalation, higher still at 19.83 MSv/h. So no, I didn't get that part wrong. Though of course these higher numbers would be relevant if the uranium contaminates the soil and water and people do start ingesting it. Obviously not 100 tonnes at a time. I didn't bother with that calculation for this reason - you have to figure out contamination rates, rates of ingestion and so on. Even though I know that in practice, contamination would affect people most by ingestion.

I'm sorry, it doesn't appear you're getting it, still. The numbers you are quoting, first, don't match those in your original post (see below), and second, make no sense. The reasons they don't make sense are, and these are merely for example, there is very much more, the inverse square law, the non-cumulative nature of radiation exposure due to your body's ability to heal if given the opportunity, if we're talking about a leak from a cask, physical limitations on the amount of exposure possible after various periods due to how slowly it would get out, and so forth.

Here's how I know: uranium miners and prospectors don't die quickly and unpleasantly, and if the figures you are quoting were true, they would. Something is not right. Either we don't understand what we're choosing on that calculator, or it's not calibrated for certain sorts of things, or something.

The source "Stack of refined uranium rods standing beside you" was not an option given for radiation source. So I chose "external radiation from soil". I assume they calculate properly for this kind of radiation. Your skin may be quite good at blocking it, but I assume some portion gets by. And apparently, that's enough to hurt you pretty badly if you've got enough natural uranium around.

The physical limitations I listed above are enough to tell me that's wrong.

No, it's 468.2 Sv/h. The calculation per year was 4.104 MSv/a. I just checked.

Go back and look at your own post. It was nothing of the kind. The figures I quoted, I cut-n-pasted. In addition, it's physically impossible for a single person to get physically close enough to 1 tonne of uranium, much less 100 tonnes, to absorb all the radiation it puts out.

Thanks for the other information. I'll look into it.

Do that. It's all linked. Sorry for the earlier confusion.

Please also stop being ridiculous; no one can get close enough to 100 tonnes of uranium to absorb all the radiation it puts out. It's not like heat, where the radiation of infrared is dependent upon the temperature, no matter whether the material is near or far and there's only inverse-square law to protect you; this isn't electromagnetic radiation, it's alpha and beta particles, and they have a very limited range in air. It's the gamma that will really get you, and those don't come from uranium much.

 

[Schneibster]

Linky ?

http://www.ecolo.org/documents/documents_in_english/ramsar-natural-radioactivity/ramsar.html

 

[Schneibster]

I think the statement about CANDU waste was mine, and I just looked up the source of my misunderstanding. CANDUs produce more weapons-grade plutonium, not plutonium in general. It's a disposal issue Canadians are concerned with.

No, they don't. First, fission of the U-235 in natural uranium can't produce more plutonium than fission of the U-235 in enriched uranium, because it can't stay in the reactor as long, and therefore gets less neutrons. Second, the sources say the plutonium in natural uranium waste is less than 0.3%, and the plutonium in low-enriched waste from a PWR is over 1%.

http://www.ieer.org/ensec/no-3/puchange.html

Yes, so? That doesn't mean there's not less plutonium in it. They're talking about the ratios of isotopes of plutonium, not the amount of plutonium present.

The absolute amount of plutonium (or at least fissile plutonium), though, is not lower in the CANDUs:

You're wrong. Plain and simple. There isn't any way for that plutonium to get made in the first place.

http://www.isis-online.org/publications/fmct/primer/Section_II_nopics.html

There's a chart at the end of the link that gives details of plutonium in reactor fuel by type of reactor.

Yes, OF THE PLUTONIUM PRESENT, PWRs have 56% Pu-239, whereas CANDUs have 66.6%. But 66.6% of 0.3% is only 0.1%, whereas 56% of 1% is 0.56%.

 

[Belz...]

http://www.ecolo.org/documents/documents_in_english/ramsar-natural-radioactivity/ramsar.html

Thank you.

 

[bobdroege7]

From

http://hss.energy.gov/HealthSafety/ohre/roadmap/achre/intro_9_5.html

A very high dose of 100 gray (10,000 rad) to the entire body causes death within twenty-four to forty-eight hours; a whole-body dose of 2.5 to 5 gray (250 to 500 rad) may produce death within several weeks.

from DRBuzzo

But in any case, in the case of U-238 it may take a while to reach equilibrium, but in most cases, if there are radioactive daughters, it will reach equilibrium relatively fast. It would only be out from being somehow separated.

For pure U-238 it will take several hundred million years to reach equilibruim, due to the number of daughter products and the long half-lives of some of the daughters as well as the long half-life of U-238. the decay rates of each isotope will eventually be equal as that is what equilibrium means. Rate of generation equals rate of decay. And it will continue to increase in radioactivity until equilibrium is reached.

Used fuel bundle radiation levels indeed can be lethal

from

http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=5295958

Maximum exposure rates varied from 36,000 R/h next to a 3.5 year old PWR bundle with a 30,000 MWD/MT burnup

That's a lethal dose in one minute
If you want to stand next to one, be my guest, but the licensee would soon be a no longer licensed entity.

radiation decreases with the square of the distance is for point sources and other more higher exposures may be expected with other configurations.

And I say, to those opposed to nuclear waste storage in their backyard, well no FDG for you. And no tech, no radiolite, no prostate cancer seeds, ect. No waste, no Ram for medical uses. That millions of unit doses a year from my employer alone.

 

[DRBUZZ0]

You might be surprised. Several of the people on this forum have no problem with spent fuel storage tanks nearby and claim that civilian nuclear waste is not hazardous after a few decades. The specific claim was that it was no more radioactive than natural uranium after 100 years and hardly more so after 30.

Actually, on this note, I should point out that this has not been substantiated, and while I haven't asked for a lot of references, this is one where I'm going to demand it, because everything I read indicates otherwise.

No. That's not acurate and I don't think anyone ever said a spent fuel rod would be as radioactive as uranium ore in 100 years. When talking about relatively short timespan waste, we're generally talking about the reprocessed and separated fission products, because most of those are very short lived. If you have fission products then really the only ones that are very long lived are I-129, Tc-99 and a few others. Low yeild percentage, so it turns out the material goes down in radiation rapidly.

That having been said I'd have no problem having fully unprocessed spent fuel in my back yard in a standard dry storage cask.

So my cursory understanding says that a stack of natural uranium as large as the spent fuel from one refueling would deliver about 100 times the lethal dose of radiation in an hour. Unless there's something I've totally screwed up.

Which might well be, because the dose calculator I used gave slightly higher doses the longer the delay. So I'd appreciate some help.

You have had much help. The spent fuel is going to vary greatly... extremely greatly from thorium-cycle reactors, thermal light water reactors, integral fast neutron reactors, breeders, high enrichment naval reactors. Also, how long the fuel stays in the reactor. This stuff is not all equal. It has a lot of the same stuff in it, but totally different proportions.

I don't know that you could effectively ever get a lethal dose from natural uranium alone. You could sit in a room with giant piles of the stuff all around you for days on end and not get acute radiation sickness.

 

[Apollo20]

Plutonium Production in a CANDU

Here are some data for Pickering ‘A’, a 540 MW(e) large CANDU reactor:

A Pickering ‘A’ fuel bundle contains about 22.5 kg of UO2 equivalent to 20 kg U, (The exact values depend on the pellet density).

The reactor has 12 bundles/channel and 390 channels giving 4680 bundles/reactor.

Hence each Pickering ‘A’ reactor contains 20 x 4680 kg of U = 93,600 kg of U.

The average burnup of Pickering fuel is 180 MWh/kg = 7500 MWd/t = 650 GJ/kg uranium

The U-235 content of a CANDU fuel bundle goes from 7.1 kg/t as installed to 2.4 kg/t at a burnup of 7500 MWd/t. (This corresponds to a 66 % utilization of the available U-235, of which 85 % produces useful energy.)

Hence 4.7 kg of U-235 has been “consumed”. The consumption is from fission and neutron capture. The fission and capture cross sections of U-235 are 580 barns and 98 barns respectively. Therefore 580/678, or 0.8555 of 4.7 kg = 4.02 kg of U-235 per tonne of uranium has been fissioned.

Pu-239 is produced at an initial rate of 1 kg/t per 1000 MWd/t. Therefore at a burnup of 7500 MWd/t there should be 7.50 kg of Pu-239 per tonne of uranium. The observed Pu-239 concentration is 2.61 kg/t so that 4.89 kg/t has been “lost”. The losses are from plutonium fission and neutron capture. The fission and capture cross sections of Pu-239 are 742 barns and 271 barns respectively. Therefore 742/1013, or 0.7325 of 4.89 kg = 3.58 kg of Pu-239 per tonne of uranium has been fissioned.

The fission of 1 kg of U-235 or Pu-239 releases 1000 MWD/t of energy. In a CANDU we have the fission of {4.02 (U-235) + 3.58 (Pu-239)}= 7.6 kg of fissioned material. Hence, the expected energy release is 7.6 x 1000 MWd/t = 7600 MWd/t, in good agreement with the 7500 MWd/t expected.

Since the reactor contains 93.6 tonnes of uranium, the total energy output is 7500 x 93.6 = 702,000 MWd. The average reactor residence time of a fuel bundle is about 1 year = 365 days. Hence the (thermal) power output of Pickering is 1923 MW. Then, because the thermal efficiency of a Pickering unit is 28 %, the electrical power output is 538 MW.

 

[Lonewulf]

That having been said I'd have no problem having fully unprocessed spent fuel in my back yard in a standard dry storage cask.

Something I don't get. Okay, let's say that something WOULD have to be stored for several millenium, and would be "just as harmful" thousands of years from now. What keeps us from remaking it's container after a certain amount of time? Obviously, we can safely store it NOW, what will keep us from safely re-making it's container 40 years from now, 100 years from now, or however long you expect it to last?

 

[Belz...]

So, Apollo... were you asking that backyard nonsense for a reason, or are you going to ignore the fact that almost everybody said they wouldn't mind ?

 

[luddite]

Please also stop being ridiculous; no one can get close enough to 100 tonnes of uranium to absorb all the radiation it puts out. It's not like heat, where the radiation of infrared is dependent upon the temperature, no matter whether the material is near or far and there's only inverse-square law to protect you; this isn't electromagnetic radiation, it's alpha and beta particles, and they have a very limited range in air. It's the gamma that will really get you, and those don't come from uranium much.

I did look back and I've been consistent. I've also been prepared to accept I was wrong all along. Looking over the calculator, I see a lot of variables and most of the assumptions don't apply. So it may just be unable to answer the hypothetical question of what uranium will do to you if you stand next to a stockpile big enough to fuel a reactor. And maybe that's a stupid question anyway.

Now that you've agreed that spent fuel is more dangerous, can we just agree that it would be preferable to make sure the stuff is carefully controlled? That we can't just forget about it after 100 years? Feel free to say "But nobody ever said that".

 

[luddite]

Something I don't get. Okay, let's say that something WOULD have to be stored for several millenium, and would be "just as harmful" thousands of years from now. What keeps us from remaking it's container after a certain amount of time? Obviously, we can safely store it NOW, what will keep us from safely re-making it's container 40 years from now, 100 years from now, or however long you expect it to last?

The problem is that we haven't been great at keeping track of it now. In the US and Canada, the spent fuel is pretty well taken care of, but not the low-level waste or depleted uranium. The tailings get left behind and children play with them or contractors use them as building rubble. And in Russia all kinds of waste of every kind goes missing. They have no idea where all their waste is. And the fear, of course, is that you're only going to figure out that you need to rebuild the containment when you start seeing rising rates of cancers and finally trace it to the water or soil to discover there's been a breach. That's a lot of trouble to load onto the following generations. And if we've got those problems now, you'd have to multiply 15-fold to try to eliminate coal plants and even more if you try to replace cars as well. And the more of it there is, let's face it, the more careless we'll be.

 

[RecoveringYuppy]

The problem is that we haven't been great at keeping track of it now. In the US and Canada, the spent fuel is pretty well taken care of, but not the low-level waste or depleted uranium.

What exactly is your worry with depleted uranium? It's about as radioactive as a typical granite countertop.