Commercial operation of the long-shuttered second unit at the Tennessee Valley Authority’s Watts Bar nuclear plant in Tennessee got underway earlier this month, the first U.S. nuke reactor to start up since 1996, when a sister 1,150-unit came on line. The second unit went through years of tribulation after construction began in 1973, then was halted in 1985 and not restarted until  2007.

“Watts Bar Unit 2 is a key part of our commitment to produce cleaner energy without sacrificing the reliability and low cost that draws both industry and residents to our area,” CEO William Johnson said on Oct 19. Completing the partially built unit cost $4.7 billion, nearly twice the 2007 completion estimate of $2.5 billion. The original estimate also had set an in-service date of late 2012 (ENR 4/16/12 p. 14).

The estimates were based on TVA’s experience in completing a third unit at its Browns Ferry’s plant in Alabama and did not consider Watts Bar’s unique aspects. Construction was started too early and was inefficient, TVA said at the time. It began issuing quarterly updates to maintain estimate integrity and provide transparency into project performance.

The unit was about 80% complete and had a $1.8-billion investment in 1985, when TVA determined the additional power would not be needed to meet demand. About $300 million of the additional cost was related to the implementation of new U.S. Nuclear Regulatory Commission safety standards, which were mandated after the 2011 meltdown of the Fukushima nuclear plant in Japan.

TVA was criticized for awarding the construction contract based on initial cost estimates. The federal power producer did not change the engineering-procurement-construction contract, which had been renegotiated after a review of project requirements. Other challenges previously reported during Watts Bar reconstruction included removal of cables from the operating Unit 1, rather than from the under-construction Unit 2. Workers also incorrectly removed a valve that was providing a safety barrier. Work on Unit 2 was stopped when the errors were discovered.

Despite the completion, TVA has ended its plan to finish construction of a partially built reactor at its Bellefonte nuclear-plant site in Alabama, saying the power is not needed. The site, with two partially completed 1,250-MW units and about $6 billion in investments, will be sold at auction on Nov. 14, with a minimum bid of $36.4 million.