Importance of fusion stage in thermonuclear weapon

[SteamKing]

Are there reports that weapons in the US stockpile are in need of replacement? I have not seen anything near term.

All published US weapon designs rely on Pu not HEU for the primary.

Like everything else, these devices don't last forever. With testing reduced or discontinued entirely (the US has not held a nuclear test since 1992), one is less certain of correct device operation with the passage of time.

HEU is required to make plutonium and other radioisotopes, and it can be used as fuel for commercial and military reactors. The uranium doesn't enrich itself. There are other critical nuclear materials besides HEU.

After the Savannah River nuclear reactors were shut down in 1988, there was no US production of tritium until a facility came on-line at Watts Bar. Radioisotope production for commercial or medical use also depends on having access to reactors where this material is bred; some isotope supplies now can only be obtained from Canadian reactors.

 

[mheslep]

Plutonium can be produced with natural uranium; indeed the Pu for the Nagasaki weapon was made this way. That is, neutrons are required to productively make uranium into plutonium which are generated by any moderated critical reaction. HEU, i.e. weapons grade uranium, could be used instead of the common LEU in power reactors, perhaps it is, but it not is required.

Similarly, I don't see any physics driven need for stored tritium in modern thermonuclear weapons. I know the early thermonuclear weapons used stored Tritium, but given the short half life it seems that reliance on production at detonation time from Li-6 would be imminently more practical.

From what I have read and gathered, much of the expertise in the US nuclear weapon program was engaged in building "advanced new types" of nuclear weapons up until the 1990s and the signing of the CTBT, which effectively restricts new weapons ( http://www.fas.org/bethecr.htm). In any case, I would expect a switch from new design and development to stockpile stewardship would bring about a reduction in visible staffing and facilities.