Reliable: Nuclear reactors provide base-load power and are available over 90% of the
time; intervals between refuelings have been extended and down time for refueling
has been reduced. In the USA, these improvements over the years have been the
equivalent of adding one reactor a year to the existing fleet. Most reactors are
designed for a life of 40 years; many are reaching that age in good condition and
extensions of 20 years have usually been granted.