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Not sure if this belongs here, Chemistry, History, or some other Stack Exchange site, but I'll start it here and welcome migration to a different site if appropriate.

In doing some reading on the history of the Manhattan Project, and then subsequent later nuclear weapons research, it's obvious that a huge amount of electrical power is typically required to refine, reduce, separate, and enrich uranium and plutonium (and likely other materials as well) which go into the "boom" part of the weapon fuel. Although a nuclear explosion releases a huge amount of energy in an extremely brief period of time, how does this compare to the amount of energy that would have been used to generate the fuel material in the first place, over months and years of processing and enriching from raw materials? Obviously there are lots of variables, both in fuel refining, as well as explosive yield, and so ballpark answers are perfectly acceptable to me.

Just wondering if nuclear weapons are "energy negative", when comparing what was used to produce the weapon, compared to explosive yield.

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    $\begingroup$ Do you think nuclear power plants are net negative? $\endgroup$
    – Jon Custer
    Commented Sep 24, 2021 at 22:10
  • $\begingroup$ Nuclear weapons need higher grade materials than power plants do, so an answer for power plants may not be the same as for weapons. $\endgroup$
    – Dale
    Commented Sep 24, 2021 at 23:01
  • $\begingroup$ Ye plutonium does no require that treatment. $\endgroup$
    – Jon Custer
    Commented Sep 25, 2021 at 0:38
  • $\begingroup$ Use of Pu requires reprocessing of spent reactor fuel. $\endgroup$
    – John Darby
    Commented Dec 19, 2021 at 5:55

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The Fat Man detonation which destroyed Nagasaki is said to have released 88 TJ, or 24 GWh of energy, which is pretty small by the standards of modern H bombs, 1-50 PJ or 270 to 13,500 GWh.

On the other hand, according to this (http://www.ipsr.ku.edu/ksdata/ksah/energy/18ener7.pdf) the State of New Mexico in 2019 used about 11,000 GWh in a whole year, or about 2-3 modern high end H bombs. And the state's energy usage is at least double what it was in 1945 I imagine, based on overall US trends.

So given all the development cost, e.g. all the centrifuges running for months on end to enrich, it's hard to say if the original nukes were energy positive, but the modern ones definitely are, or would be if they were ever used.

Let's hope that return on investment never gets realized.

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  • $\begingroup$ Counting all the energy costs for a thermonuclear weapon (or for an older fission-only weapon), the weapon is energy negative. Please see my response. $\endgroup$
    – John Darby
    Commented Dec 19, 2021 at 6:07
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It turns out that nuclear enrichment on the bleeding edge of technology was not all that efficient. It relied on many high-current wires to generate the electromagnetic fields needed for enrichment. This power consumption, and the associated borrowing of silver from the US Treasuriy for wiring (so as not to draw attention by consuming copper) is documented in the American Scientist article, From Treasury Vault to the Manhattan Project.

By mid-July the facility had produced slightly more than 50 kilograms. By this time Y-12 had consumed about 1.6 billion kilowatt-hours of electricity, about 100 times the energy yielded by the bomb called Little Boy, which was dropped on Hiroshima on August, 6, 1945.

So these bombs were decidedly energy negative.

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  • $\begingroup$ Another reason silver was used instead of copper was due to the limited supply of copper during the war and the superior conduction properties of silver. $\endgroup$
    – John Darby
    Commented Dec 19, 2021 at 5:47
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The energy to use a bullet should consider the energy to produce the rifle as well as the energy to manufacture the bullet. Similarly, the energy to use a nuclear weapon should consider the energy to produce the entire weapon, not just the nuclear material in the weapon.

A modern, high-yield thermonuclear nuclear weapon releases much power but relatively little energy, compared to the energy required to develop and deploy the weapon. The energy required to develop and deploy the weapon requires funding and facilities for large staffs of scientists and engineers, mining of U ore, removal of U from the ore, construction and operation of facilities (reactors for Pu, centrifuges for enriched U), reprocessing of spent reactor fuel for removal of Pu, generation and manufacturing of materials for the secondary for a thermonuclear device, generation and manufacturing of other special materials (classified), fabrication into a weapon, testing of initial designs, development of deployment systems (ICBMs, SLBMs, bombers), actual continual deployment on bombers and missiles on various military bases and submarines, round the clock security, and scheduled maintanance.

The massive power from the weapon is what causes its tremendous damage.

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