3 ms·

One point that's commonly missed in the lay discussions is that the stuff with a really long half-life (e.g. uranium/plutonium) is not that radioactive/harmful;

One point that's commonly missed in the lay discussions is that the stuff with a really long half-life (e.g. uranium/plutonium) is not that radioactive/harmful; by definition if it takes you 100k years for 50% of your unstable nuclei to decay, the emission rate per second is very low. In contrast, the really nasty stuff has a very short half-life, and emits radiation at a very high rate for a very short duration. These can be more like 10s of years half-life. The counterpoint is that they become mostly non-radioactive in 100s of years, not 100s of millenia. The actual environmental risks from long-half-life radioactive substances are pretty minimal as far as I can see. The US makes this problem a lot worse than it needs to be by declining to reprocess nuclear fuel (I believe on proliferation concerns). Reprocessing is done in Europe, China, and Russia. You can separate the uranium & plutonium in spent fuel rods from the shorter-lived and much more nasty fission products, reuse the uranium, do something safe with the potentially weapons-grade plutonium, and then handle / store the separated fission products in a shorter-term facility. The design goals of Yucca Mountain were assuming that you need to keep nuclear fuel safe for 100k years; that's an intensely challenging design constraint. If we just need to keep something safe for 100s of years it becomes much more tractable. See https://www.nrc.gov/reading-rm/doc-collections/fact-sheets/radwaste.html https://www.nrc.gov/reading-rm/doc-collections/fact-sheets/r... for some further reading.

sbierwagen 6y ago
>do something safe with the potentially weapons-grade plutonium Reprocessed plutonium from a civilian power reactor would never be weapons-grade, it has too much Pu-240 in it: https://en.wikipedia.org/wiki/Reactor-grade_plutonium https://en.wikipedia.org/wiki/Reactor-grade_plutonium It is claimed that it is possible to make weapons from reprocessed plutonium, but the warheads would need active cooling and exotic pit geometries, making them not so amendable to miniaturization.
- rwcarlsen 6y ago
  It looks like you replied to the wrong sibling comment.
  - sbierwagen 6y ago
    I have edited my comment to make it clearer which sentence I was replying to.
- theptip 6y ago
  Thanks, I wasn't aware of that detail. This makes the anti-proliferation position of the US from the '70s to this day even more perplexing. Do you have any insight/thoughts on why the US made this push to prevent reprocessing, if it's not actually possible to use that process to build a warhead? Is it possible that they discovered a pathway in their nuclear tests that has remained classified? Or could it be an error/overly cautious policy position that just hasn't been updated since the '70s?
  - philipkglass 6y ago
    Do you have any insight/thoughts on why the US made this push to prevent reprocessing, if it's not actually possible to use that process to build a warhead? "Additional Information Concerning Underground Nuclear Weapon Test of Reactor-Grade Plutonium" https://www.osti.gov/opennet/forms?formurl=document/press/pc29.html https://www.osti.gov/opennet/forms?formurl=document/press/pc... A successful test was conducted in 1962, which used reactor-grade plutonium in the nuclear explosive in place of weapon-grade plutonium. The yield was less than 20 kilotons. This test was conducted to obtain nuclear design information concerning the feasibility of using reactor-grade plutonium as the nuclear explosive material. The test confirmed that reactor-grade plutonium could be used to make a nuclear explosive. This fact was declassified in July 1977. The release of additional information was deemed important to enhance public awareness of nuclear proliferation issues associated with reactor-grade plutonium that can be separated during reprocessing of spent commercial reactor fuel. The Carter reprocessing ban was enacted in April 1977, a few months before this information was released to the public. There is no evidence that any existing nuclear weapons state has started with plutonium reprocessed from civilian power reactors. Building "production" reactors that produce plutonium without generating electricity is easier and the plutonium quality is higher. However, reprocessing commercial fuel is a potential loophole for nations that want to maintain a latent nuclear weapons capability as a plausibly deniable part of a civilian nuclear power program. There are indications that Japan values its reprocessed plutonium from civilian reactors in this light. More pointedly, would Saudi Arabia, Israel, or the US trust an ostensibly civilian Iranian nuclear power program that included plutonium separation and reprocessing? Would Iran trust a Saudi program of the same type? The high Pu-240 content of spent nuclear fuel from commercial reactors is not a strong enough technical barrier against weapons use to be reassuring in circumstances of low initial trust between parties. That's why it makes at least some sense that the United States did not want reprocessing to be a routine feature of civilian nuclear power programs. ======================== EDIT: everything following this line ^ is very speculative, so take with a shaker of salt. But I think it's an interesting idea that I haven't seen anyone else write about. There are some exotic chemical reactions that give rise to mass-independent isotope fractionation [1]. For isotopes subject to this effect, enrichment can be more efficient via these mass-independent effects than would be indicated by conventional mass-dependent enrichment mechanisms like gas diffusion or centrifuge enrichment. There is evidence that these effects apply in uranium. The behavior is to separate even and odd isotopes rather than heavy and light isotopes [2]. If a similar mass-independent enrichment process were discovered for plutonium, it would mean a couple of things: 1) It might be industrialized secretly, in the context of weapons, long before it becomes a publicly known process with corresponding anti-proliferation safeguards and targeted inspections. 2) It would mean that aged spent nuclear fuel from commercial reactors could become an excellent raw material for making weapons plutonium. The other major contaminant isotope, Pu-241, has a half life of only 14 years. A few decades of cooling largely eliminates it. Then the Pu-240 would be separated from Pu-239 by the mass-independent fractionation process. [1] https://en.wikipedia.org/wiki/Mass-independent_fractionation https://en.wikipedia.org/wiki/Mass-independent_fractionation [2] https://link.springer.com/article/10.1007/s11631-016-0109-3 https://link.springer.com/article/10.1007/s11631-016-0109-3

sbierwagen 6y ago

>do something safe with the potentially weapons-grade plutonium Reprocessed plutonium from a civilian power reactor would never be weapons-grade, it has too much Pu-240 in it: https://en.wikipedia.org/wiki/Reactor-grade_plutonium https://en.wikipedia.org/wiki/Reactor-grade_plutonium It is claimed that it is possible to make weapons from reprocessed plutonium, but the warheads would need active cooling and exotic pit geometries, making them not so amendable to miniaturization.

rwcarlsen 6y ago
It looks like you replied to the wrong sibling comment.
- sbierwagen 6y ago
  I have edited my comment to make it clearer which sentence I was replying to.
theptip 6y ago
Thanks, I wasn't aware of that detail. This makes the anti-proliferation position of the US from the '70s to this day even more perplexing. Do you have any insight/thoughts on why the US made this push to prevent reprocessing, if it's not actually possible to use that process to build a warhead? Is it possible that they discovered a pathway in their nuclear tests that has remained classified? Or could it be an error/overly cautious policy position that just hasn't been updated since the '70s?
- philipkglass 6y ago
  Do you have any insight/thoughts on why the US made this push to prevent reprocessing, if it's not actually possible to use that process to build a warhead? "Additional Information Concerning Underground Nuclear Weapon Test of Reactor-Grade Plutonium" https://www.osti.gov/opennet/forms?formurl=document/press/pc29.html https://www.osti.gov/opennet/forms?formurl=document/press/pc... A successful test was conducted in 1962, which used reactor-grade plutonium in the nuclear explosive in place of weapon-grade plutonium. The yield was less than 20 kilotons. This test was conducted to obtain nuclear design information concerning the feasibility of using reactor-grade plutonium as the nuclear explosive material. The test confirmed that reactor-grade plutonium could be used to make a nuclear explosive. This fact was declassified in July 1977. The release of additional information was deemed important to enhance public awareness of nuclear proliferation issues associated with reactor-grade plutonium that can be separated during reprocessing of spent commercial reactor fuel. The Carter reprocessing ban was enacted in April 1977, a few months before this information was released to the public. There is no evidence that any existing nuclear weapons state has started with plutonium reprocessed from civilian power reactors. Building "production" reactors that produce plutonium without generating electricity is easier and the plutonium quality is higher. However, reprocessing commercial fuel is a potential loophole for nations that want to maintain a latent nuclear weapons capability as a plausibly deniable part of a civilian nuclear power program. There are indications that Japan values its reprocessed plutonium from civilian reactors in this light. More pointedly, would Saudi Arabia, Israel, or the US trust an ostensibly civilian Iranian nuclear power program that included plutonium separation and reprocessing? Would Iran trust a Saudi program of the same type? The high Pu-240 content of spent nuclear fuel from commercial reactors is not a strong enough technical barrier against weapons use to be reassuring in circumstances of low initial trust between parties. That's why it makes at least some sense that the United States did not want reprocessing to be a routine feature of civilian nuclear power programs. ======================== EDIT: everything following this line ^ is very speculative, so take with a shaker of salt. But I think it's an interesting idea that I haven't seen anyone else write about. There are some exotic chemical reactions that give rise to mass-independent isotope fractionation [1]. For isotopes subject to this effect, enrichment can be more efficient via these mass-independent effects than would be indicated by conventional mass-dependent enrichment mechanisms like gas diffusion or centrifuge enrichment. There is evidence that these effects apply in uranium. The behavior is to separate even and odd isotopes rather than heavy and light isotopes [2]. If a similar mass-independent enrichment process were discovered for plutonium, it would mean a couple of things: 1) It might be industrialized secretly, in the context of weapons, long before it becomes a publicly known process with corresponding anti-proliferation safeguards and targeted inspections. 2) It would mean that aged spent nuclear fuel from commercial reactors could become an excellent raw material for making weapons plutonium. The other major contaminant isotope, Pu-241, has a half life of only 14 years. A few decades of cooling largely eliminates it. Then the Pu-240 would be separated from Pu-239 by the mass-independent fractionation process. [1] https://en.wikipedia.org/wiki/Mass-independent_fractionation https://en.wikipedia.org/wiki/Mass-independent_fractionation [2] https://link.springer.com/article/10.1007/s11631-016-0109-3 https://link.springer.com/article/10.1007/s11631-016-0109-3