Above: Browns Ferry 2 resumed generation on 22 April, following completion of its latest scheduled maintenance and refuelling outage (Photo credit: TVA)

 

BROWNS FERRY, NEAR ALABAMA, USA, is the Tennessee Valley Authority’s largest site.

The plant comprises three General Electric BWRs with Mark I containment. Browns Ferry 1 entered commercial operation in December 1973, followed by unit 2 in June 1974 and unit 3 in July 1976. All three units have been granted 20-year operating licence extensions by the US Nuclear Regulatory Commission (NRC) allowing them to remain in service until the 2030s.

During the last weekend of February, Browns Ferry 2 begun a scheduled refuelling and maintenance outage, which included the largest scope of turbine deck work since the original construction. All three of the unit’s low-pressure turbines underwent a comprehensive replacement of major components, including new rotors, inner casings, steam piping and bellows and turbine supervisory instruments. These tasks required the support of more than 500 additional outage workers and an incredible amount of heavy lifting — with 600 separate crane lifts of components such as rotors weighing up to 150t and inner casings weighing up to 90t.

The upgrades will allow the unit to generate an additional 7MW of electricity.

“This investment by TVA helps ensure Browns Ferry continues to provide safe, reliable, clean energy to our local power companies as we enter the region’s summer peak season and beyond,” said Browns Ferry site vice president Matt Rasmussen. “The work completed during this outage demonstrates our team’s high level of commitment to our mission of service and to the people living in the communities we serve.”

 

Above: Browns Ferry Unit 2 rotor replacement (Photo credit: TVA)

 

Fuel innovations

While major upgrades were happening on the turbine deck, the refuelling team loaded four new 3D-printed fuel assembly brackets into the reactor. The brackets demonstrate the latest innovations in additive manufacturing and artificial intelligence. They were manufactured at Oak Ridge National Laboratory in a joint project with TVA and the utility’s fuel supplier, Framatome, as part of Oak Ridge’s Transformational Challenge Reactor programme. The components are the first of their kind loaded into a commercial reactor.

ORNL additively manufactured channel fasteners for Framatome’s BWR fuel assembly using a micro-welding process. The team created a 3D-printed part that is compliant with reactor safety regulations for deployment in a commercial reactor. The lab is also providing all the 3D digital data captured during the manufacturing process. This details each layer of the 3D print, information that can be used to certify the quality of the bracket.

The channel fasteners, which perform an essential function in the fuel assembly, were installed on Atrium 10XM fuel assemblies at Framatome’s nuclear fuel manufacturing facility in Richland, Washington.

The channel fasteners secure the fuel channel to the BWR fuel assembly. The fuel channel wraps around the assembly and guides coolant flow up through the fuel rods. Channel fasteners have traditionally been fabricated from expensive castings and required precision machining. Additive manufacturing is a more efficient way to achieve the tight specifications of these components, Framatome explained.

“Being the first to use these additively manufactured components supports an innovative manufacturing approach that could pave the path for use across the existing nuclear fleet and in advanced reactors and small modular reactors,” said Dan Stout, TVA’s director of nuclear technology innovation.

The brackets will remain in the reactor for six years with Inspections planned during outages and after removal.