The Obama administration has finally cleared the way for the publicly owned and operated Tennessee Valley Authority (TVA) to fire up a “new” nuclear reactor on which construction began nearly 20 years ago.

Based on cost estimates dating back to December 2012, the final price tag for TVA’s Watts Bar Unit 2 will be something north of $4.5 billion. Worse, when Unit 2 finally goes into operation next month, or early next year, its technology already will be out of date.

Why did it take 20 years to get here? Isn’t this a disservice to taxpayers?

Part of the answer, of course, is safety concerns. Memories of the accidents at Pennsylvania’s Three Mile Island, Russia’s Chernobyl and Japan’s Fukushima still resonate in the public’s consciousness.

Never mind that most of France’s electricity is generated problem-free by nuclear-powered plants. Apparently, the very small chance of another accident here at home was more than enough, until recently, to deter risk-averse politicians and bureaucrats from promoting nuclear energy.

But that’s really an excuse, not a reason. If nuclear energy was unsafe, those same politicians and bureaucrats would have rushed to shut down every one of the nearly 100 nuclear reactors operating in the United States. They didn’t — because they know better.

They also know that nuclear power is a carbon-footprint-free technology. But that too wasn’t enough. In fact, President Obama’s recently released “Clean Energy Plan” is almost totally silent on the nuclear power option.

It turns out that construction on TVA’s Watts Bar Unit 2 reactor was stopped in 1988 because of a scandal involving agency officials and contractors. The reactor was about 80% complete at the time. Building resumed in 2007; but some five years later, in February 2012, the project was still languishing, over-budget and behind schedule.

Finally, on Oct. 22 this year, the Nuclear Regulatory Commission (NRC) granted the TVA an operating license for Unit 2, allowing fuel to be loaded and pre-startup testing to begin, with 1,800 megawatts of power generating capabilities expected to be fully online by year end or next spring at the latest.

Cost overruns and construction delays are business as usual for public works projects like TVA’s Watts Bar Unit 2. Anyone who has seen a slow-motion road crew in inaction knows the drill exactly. But road building doesn’t typically involve high technology. Nuclear power does.

The nearly 20 years it took to complete Unit 2 from start to finish means that some of the technologies embodied in the “new” reactor already are old.

Unit 2 is what is known as a “Generation II” reactor. It is probably the last one of its type that will ever be placed in operation anywhere. While Washington stood still, the world moved on. Generation III reactors are now state of the art, incorporating numerous design improvements resulting from long experience with Generation II units.

Generation III reactors already have been installed in Canada, Japan and France. None exist in the United States, though the World Nuclear Association anticipates that four to six new units could come online by 2020 — if Washington doesn’t create unnecessary roadblocks. Generation IV reactors are on the drawing board, but these aren’t expected to be operational until the 2030s.

Nuclear power is not some weird futuristic sci-fi technology. The United States, in fact, is the No. 1 producer of nuclear power on the planet, accounting for nearly a third of humankind’s nuclear-generated electricity, the World Nuclear Association points out. It is clean, safe and reliable (much more reliable than solar and wind power).

U.S. politicians who are legitimately concerned about the impact of fossil fuel combustion on the world’s climate should be among the strongest advocates of nuclear energy. But most of them are silent or merely pay it lip service .

The NRC’s decision to license the operation of another nuclear reactor in the Tennessee Valley deserves one-and-a-half cheers. Were it not for the time and money the government unnecessarily squandered on the project they might get three cheers.