That plant is exactly as old as the current USD currency regime. So it's already >50 years old...by 2040 it will be close to 70 years old. Xcel got approval to expand waste storage on the site so that will allow them to seek approval for operation until 2040.

"Xcel has proposed extending the operating life of the Monticello plant to 2040. To accommodate the additional used nuclear fuel associated with extending the lifetime of the plant, Xcel requested that the Minnesota PUC authorise additional storage within the plant's existing independent used fuel storage installation. The utility estimates that about 14 additional used fuel storage canisters will be needed to facilitate plant operations through to 2040."