The high cost is a myth. A nuclear reactor produces so much energy in its life that the decommissioning costs are only a small fraction of the kWh sold on the market. Do you want to double the reserve? Fine, it would still be economically valid.
That said, the "usability" of the land is a moot point. How "usable" is the land of a hydroelectric basin that is permanently made unusable *by design* ?