The Tennessee Valley Authority board in the US has approved continuing with construction of the second generating unit at Watts Bar Nuclear Power Plant located on the Tennessee River near Spring City following a revised estimate.

The estimate presented to TVA in early April, revealed the project requires an additional $1.5bn to $2bn to complete, bringing the total cost to complete the unit at nearly $4.5bn, with the most likely estimate of $4.2bn.

The seven-month long analysis of the construction project identified corrective actions for project management and a cost estimate and milestone schedule.

TVA president and CEO Tom Kilgore said the company expects Watts Bar Unit 2 to be among the best operating and most economical nuclear generating facilities of the 21st century.

"The safe and quality completion of Watts Bar Unit 2 will help us deliver a balanced mix of energy sources and increase our supply of emission-free electricity," added Tom.

Estimated completion of the project is between September and December 2015 and currently site improvement works are under way.