I sure am glad I'm not at COMSUBPAC for this analysis
The USS HONOLULU (SSN 718) is decommissioning after its current deployment. It has a lot less fuel remaining than its sister ship, the USS SAN FRANCISCO (SSN 711), which refueled in 2002.
However the USS HONOLULU has an asset the SF lacks-- an operations compartment that actually passes all the pertinent QA tests. SF has been up on the blocks for over a year while the nation's best naval architects stand around uttering variations on "Gee, uh, I awlways wanted to work on one of they-em!" and jack up the repair bill.
Refueling the HONO and scrapping the SF would have been one option-- about $170M.
But it turns out that it's cheaper to slice the front end off the HONO and weld it to the rest of the SF. $79M and no radcon-- a bargain at any price.
I'm sure it's going to turn out to be more complicated than that. But what a project!
BTW in 1986 the U.S. Navy calculated that covering all its mission requirements would require 125 SSNs. Today we're struggling to stay above 50 while building multi-b-b-b-BILLION submarines, so $79M is truly worth watching your tax dollars at work.