Even the reactor tanks themselves can be replaced by newer ones when the old ones become brittle. It has been done already in the US, IIRC.

Nuclear plant refuelling is always done during summer, in Sweden at least. At that time, demand is so low anyways that the slack can be picked up by our hydroplants without a hitch. And not all nukes need to be refueled at the same time. A standard refueling operation takes a few weeks.

Peak oil is not an energy crisis. It is a liquid fuel crisis.