First criticality for Watts Bar 2

24 May 2016

The Tennessee Valley Authority's (TVA) newest nuclear reactor, Watts Bar unit 2, has reached first criticality. The 1165 MWe (net) pressurized water reactor is the first nuclear unit to start up in the USA since Watts Bar 1 in 1996.  

Operator Todd Blankenship monitors reactor conditions ahead of initial criticality at Watts Bar 2 (Image: TVA)  

Watts Bar 2 is the second unit to be built at TVA's site near Spring City, Tennessee. Its construction began in 1972, but work was suspended in 1985 when the unit was about 55% complete. TVA decided to resume work on the unit in 2007, awarding an engineering, procurement and construction contract to Bechtel.

TVA received an operating licence for the unit from the US Nuclear Regulatory Commission in October 2015 and fuel loading was completed in December. The reactor achieved first criticality - its first sustained nuclear fission reaction - at 2:16 am EDT yesterday and is now generating heat under its own power. TVA said that the unit was operating in a stable condition at low power levels that will slowly be increased over the coming weeks as it moves towards commercial operation.

Plant systems and controls will be monitored and tested at various power levels up to 100%. The unit is expected to enter commercial operation later this summer.

Watts Bar 2's completion has incorporated upgrades in response to the Fukushima Daiichi accident of 2011 required by the NRC of all US nuclear power plants. Enhancements include a new hardened FLEX equipment storage building designed to withstand earthquakes, floods and other incidents similar to those that occurred in Japan. This houses emergency backup diesel generators, pumps and other equipment needed to keep the reactor containment cooled in the event that onsite power is lost.

The total estimated project cost of $4.7 billion was approved by TVA's board in February. Orders related to post-Fukushima regulatory requirements and cyber security issues have increased by $125 million TVA's original $4.5 billion estimate to complete the project.

In addition to Watts Bar, TVA also operates three boiling water reactors at Browns Ferry in Alabama and two PWRs at Sequoyah in Tennessee. The company recently decided to sell another partially built nuclear power plant, Bellefonte in Alabama, after deciding that it will not need to build any new large-scale baseload capacity for at least the next 20 years. Bellefonte was to have been home to two B&W pressurized water reactors, but construction was suspended in 1988, when unit 1 was about 90% complete and unit 2 58% complete. The units' levels of completion are now substantially lower, as in the interim many components have been transferred or sold while others would now need to be upgraded or replaced.

The company is continuing to explore small modular reactors (SMRs) as a potential long-term resource and recently submitted the first early site permit application for an SMR - at Clinch River, Tennessee - to the NRC.

Researched and written
by World Nuclear News