Techniques are not capable of use for nuclear weapons.
Here's how this works.
Uranium 238 [FUEL grade]is not fissible (will not CREATE a fission nuclear chain reaction)
Uranium 235 [WEAPONS grade] is fissible. It does create a fission nuclear chain reaction.

Uranium-235 is an isotope of uranium making up about 0.72% of NATURAL uranium. Unlike the predominant isotope uranium-238, it is fissile, i.e., it can sustain a fission chain reaction.

U 238 can be /downblended/ to convert some* (very little) U 235 BUT the process also creates U 232, 233, 234, 236, 237
AND less 238 than they started with.

Depleted uranium (used as fuel already) has less 235 than natural ore.
Reprocessed uranium has less 235 than depleted uranium.
Downblended uranium has almost the full spectrum of isotopes and less 235 than reprocessed uranium.
They all need 235 in critical mass to weaponize.
Open source info.

The LAW OF CONSERVATION OF MASS. You CANNOT end up with more of a reactant after a chemical reaction. The conversion of mass into energy leaves LESS MASS than before the reaction.

So the early deal, the one they didn't go for, the one that was far better for US than the current proposal, offered them FUEL [U 238](what they claimed they wanted for economic reasons) in exchange for UN safety inspections at ANY time and lifting of sanctions. They DIDN'T TAKE that deal. They didn't trust Argentina so we tried France. They didn't want France so we tried THEIR ally and military supplier Russia and they still DIDN'T TAKE THE DEAL. They didn't want U 238 because they already had 238. 238 isn't fissible. So now they have, you guessed it, U 238. They're burning up 238 to get less 238 and less 235 than natural ore. They're not using FUEL as FUEL they're WASTING FUEL to get LESS fuel and LESS 235 than they had to start with. Funny thing about chemical reactions, you can't STOP them in the middle. You may be able to slow them down by cryogenic means but as soon as they leave the LABORATORY that ability is gone.