Last week, the Nuclear Regulatory Commission issued the first new operating license for a nuclear power plant in more than 20 years. The license was given to the Tennessee Valley Authority for its Watts Bar Unit 2 reactor located in Spring City, Tennessee, which has been in development limbo for the past 40 years. After finally finishing construction on the site and undergoing numerous inspections, TVA can now start loading uranium into the reactor and begin generating electricity. The license grants TVA authority to operate Watts Bar Unit 2 for the next 40 years.

Watts Bar Unit 2 has had the "longest construction history of any reactor in the world," according to the Bulletin of the Atomic Scientists. Construction first began on the reactor in 1972, but things came to a halt in 1985 when it was only 60 percent complete. At that point, TVA had spent $1.7 billion on the project, much more than the estimated $825 million it would take to build both Watts Bar Unit 2 and its identical twin, Unit 1.

Watts Bar Unit 2 has been in development limbo for 40 years

TVA only started working on the site again in 2007. But after the Fukushima disaster in 2011, the agency had to comply with a new host of safety regulations, further delaying completion of the reactor. Watts Bar Unit 2 is the first reactor to meet the new Fukushima-related safety orders issued by the NRC. The total cost of completing Unit 2 and complying with these regulations is thought to be around $4.5 billion.

These high construction costs may explain the licensing hiatus, and why there are so few reactors scheduled to start up operations soon. Only four reactors are expected to power up by the end of 2020, and currently, just 100 nuclear power plants in the US provide 19.6 percent of the electricity for the nation. Other power alternatives, like natural gas, serve as much cheaper options for producing electricity, requiring less initial investment than nuclear power. However, newly implemented carbon emission regulations may heighten the cost of maintaining natural power plants, making nuclear power a more favorable option.