2
$\begingroup$

Does humankind know technique to transform uranium 238 to uranium 235 ? Is it using it for obtaining uranium 235 for nuclear plants ? Or is it selecting uranium 235 from uranium ? Why not transform uranium 238 to 235 ? This would be more efficient, isn' it ?

$\endgroup$
2
  • $\begingroup$ sorry, I mean nuclear plant. ok, I fix it $\endgroup$ – Mathieu Krisztian Nov 7 '19 at 11:47
  • 1
    $\begingroup$ A third option is to "use" U-235 while still in the original natural uranium isotope mix. See en.wikipedia.org/wiki/CANDU_reactor $\endgroup$ – DJohnM Nov 7 '19 at 21:49
6
$\begingroup$

Yes, we can convert uranium-238 to uranium-235, but the last step of the conversion is a very slow process, so it's not practical. The standard way to obtain U-235 is to separate it out from natural uranium, typically using uranium hexafluoride; see Enriched uranium for descriptions of the various techniques.

Here are the steps to convert U-238 to U-235.

  1. Irradiate U-238 with neutrons to produce U-239, which has a half-life of about 23.45 minutes.
  2. U-239 beta decays to neptunium-239, which has a half-life of about 2.356 days.
  3. Np-239 beta decays to plutonium-239, which has a half-life of 24,110 years.
  4. Pu-239 alpha decays to U-235.

Obviously, waiting 24,110 years is not practical. ;) But that's ok, because plutonium-239 is fissile, so it can be used as reactor fuel and in the production of fission weapons.

The above half-life data comes from https://en.wikipedia.org/wiki/Isotopes_of_uranium#Uranium-239 and https://en.wikipedia.org/wiki/Plutonium-239

$\endgroup$
3
  • $\begingroup$ Thanks a lot PM 2Ring. $\endgroup$ – Mathieu Krisztian Nov 7 '19 at 11:48
  • 2
    $\begingroup$ Substituting plutonium for uranium does lead to completely different design and engineering problems in both reactors and weapons... $\endgroup$ – DJohnM Nov 7 '19 at 21:45
  • $\begingroup$ @DJohnM That's certainly true, I didn't intend to imply that all fissile isotopes are equal. But that's a topic for another question, and questions about reactor design are possibly better suited to the engineering site. $\endgroup$ – PM 2Ring Nov 8 '19 at 3:28

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.