I’m aware that the PWR2 Core H can be refuelled but at significant expense & time. As stated in the attached article “
In December 2015, HMS Vanguard entered a ‘Long Overhaul Period and Refuel’, which was expected to take about 3 years and cost around £200m. It took almost seven years.” This was the first (&, at this stage, only) PWR2 Core H refuel.
Obviously, most people would prefer that the money was invested in a newer, more capable submarine rather than paying a premium to keep old submarines in service. If it’s at all possible, it makes sense to expedite the design of the SSN(R) - especially if it enables an ally to increase the fleet numbers by 8+.
HMS Vanguard refuel