Nuclear plants were originally issued 40-year operating licenses by the Nuclear Regulatory Commission. Most utilities had applied for 20-year renewals for their nuclear units, and have operated them for 50 to 60 years. Many utilities are now considering applying for a second renewal and four plants have begun that decade-long process. The initial operating license for nuclear units was issued for 40 years because it was believed that nuclear plants would last 40 to 50 years. But, they, like coal plants, have operated for much longer, providing reliable and relatively inexpensive electricity.