The Inspection Beat Goes on at Watts Bar Unit 2

William Jones
Director of the Division of Construction Projects
Region II

An NRC Construction Resident Inspector watches TVA staff install the reactor pressure vessel inside the containment building at Watts Bar Unit 2.
An NRC Construction Resident Inspector watches TVA staff perform construction activities at Watts Bar Unit 2.

The NRC has issued an operating license to the Watts Bar Unit 2 reactor in Tennessee, bringing the U.S. to 100 commercial reactors. The plant’s owner, the Tennessee Valley Authority, had restarted construction of the incomplete reactor in 2007 and updated its application for Unit 2’s license in 2009.

Since 2007, NRC inspectors have devoted more than 200,000 hours to supporting the agency’s decision that Unit 2 qualifies for a license. There’s more to do, however, before Unit 2 starts splitting atoms and generating electricity, and the NRC’s going to keep an eye on all of that.

The NRC’s two permanent Resident Inspectors at Watts Bar have another full-time resident inspector and additional regional inspectors on site during this period. The inspectors and NRC management follow a well-defined process to monitor a plant as it starts up for the first time.  One of the most obvious steps we’ll monitor is when TVA loads the uranium fuel into the Unit 2 reactor.

Once Unit 2 is ready for the initial reactor startup, the NRC staff will verify TVA has properly calibrated the instruments that monitor the chain reaction even at the lowest sustainable level. The plant operators must also show they can manually shut off the chain reaction. When all those steps are done, the NRC inspectors will watch the operators’ actions as they let Unit 2 start splitting a very small number of atoms.

The next step involves testing the reactor at very low power levels. The chain reaction is affected by changes in coolant water temperature and chemicals in the water. The NRC inspectors will examine the low-power tests to ensure the plant has properly measured changes in the reaction.

As each of these tests is passed, Unit 2 will increase power in small steps and examine the reactor’s response to abnormal events. For instance, if the plant’s turbine stops running the reactor’s heat has lost its normal outlet, so the reactor must shut down. The reactor must also respond properly to shutdown commands from alternate control stations and a simulated loss of power from the electric grid.

If TVA successfully completes all of these steps, Unit 2 will be ready to add about 1,100 megawatts to the electric grid in the Southeast. During this entire process, the NRC’s inspectors will also be gathering and analyzing the information needed to gauge Unit 2’s safety performance under the agency’s Reactor Oversight Process. This process will guide NRC actions at Unit 2 as long as the plant continues to operate.