TVA is readying to bring Unit 2 at its Watts Bar nuclearplant into commercial operations.

Source: TVA

The TennesseeValley Authority has finished critical safety and reliabilitytesting on its new nuclear unit at Watts Bar.

The long-delayed and over-budget Unit 2 safely returned tofull power after completing its final power ascension test, a 50% loadrejection from full power, on Sept. 30, according to the federal utility.

Following extensive testing, Unit 2 is now generating over1,150 MW of clean energy, TVA said. The unit will now undergo an operationsreliability period of extended full power generation before beginningcommercial operations.

Construction on Watts Bar units 1 and 2 began in the early1970s, but work on unit 2 was canceled in 1985 after the utility spent $1.7billion. Watts Bar 1 started running in 1996. When TVA resumed construction onWatts Bar 2 in 2007, it estimated that finishing the reactor would cost $2.5 billion,but later revised the budget to between $4 billion and $4.5 billion.

The U.S. Nuclear Regulatory Commission a license for Watts Bar 2 inOctober 2015. The unit in December 2015 became the first nuclear reactor in almost two decadesto receive its initial load of fuel into its core, signaling that the projectis now a "fully operational nuclear reactor."

Watts Bar Unit 2 achieved initial criticality in May by generating heatunder its own power for the first time. The reactor officially synced to thegrid on June 3, when it started running at 14% of its full power output.

Following a transformer fire in an onsite, exterior switchyard at Unit 2 on Aug.30, Unit 1 was removed from service as a precautionary measure. The fire wasreported to the NRC as an "unusual event" and considered to be theleast severe emergency classification.

The fire "did not directly impact Unit 2's systems,which responded exactly as designed," TVA said in a statement. "Powerascension testing was temporarily placed on hold while the affected transformerwas replaced and operators completed a thorough inspection and testing processon affected switchyard equipment."

Output from both units combined will supply enoughelectricity to power 1.3 million homes, the utility noted.

The energizing of Watts Bar unit 2 is a critical part ofTVA's goal to generate more than half of its energy from nonemittingsources by 2020.