Are there any credible documents or even credible speculation about what would happen if, say, the Soviet Union (and then subsequently the Russian Federation) fell into civil war, and how Western powers would respond to the Russian nuclear question?

I realize this is a hyper-specific and somewhat long-winded question. Is there any credible literature regarding the potential collapse of the Soviet Union (or subsequently the Russian Federation) into civil war or warlordism, specifically addressing how the West would ensure no rogue elements, or the Russians themselves, retained the nuclear arsenal?

I understand that the nature of these contingencies is likely top-secret; for all we know, an agreement exists with China to split responsibility by longitude.

Still, I've always been curious if there is any declassified or academic literature on extracting Russian nuclear capabilities in the event of a state collapse.