TVA Sees Yellow for Flood Prevention

Wednesday, March 20, 2013 @ 05:03 PM gHale


Tennessee Valley Authority (TVA) faces six violations for failing to adequately protect Sequoyah and Watts Bar nuclear plants from the potential for failure of earthen dams upstream and flooding that would ensue.

The regulators call the flooding probable maximum flood — an event that would surpass any known local weather occurrence.

RELATED STORIES
WI Nuke Signing Off May 7
Reactor Metal Shock Could Shut Nuke
Feds Step Up PA Nuke Inspections
FitzPatrick Nuke Repairs Underway

The Nuclear Regulatory Commission (NRC) said its inspectors cited the TVA with six violations and placed Sequoyah and Watts Bar under “yellow” safety flags, indicating what NRC calls “substantial safety significance.”

NRC ranks safety findings as white, yellow and red, in increasing order of significance. If a plant is completely safe, it gets a green rating.

TVA officials said there is no immediate safety concern because the utility has implemented interim measures to protect the plants against dam failure and will continue to work with the NRC.

“The safety of our day-to-day nuclear operations has not been brought into question,” said TVA spokesman Mike Bradley. “TVA takes its regulatory compliance seriously and has already responded to the extreme flooding issues identified by the Nuclear Regulatory Commission.”

TVA discovered the potential for flooding several years ago when preparing to seek new construction licensing for the mothballed Bellefonte Nuclear Plant.

TVA officials realized the assumptions they used to model potential flood problems three and four decades ago were erroneous in their original calculations and outdated.

Weather patterns have since changed, and TVA also has since changed the way it manages river levels. When utility engineers applied correct figures and new technology to their calculations, they realized a catastrophic — and unlikely — probable maximum flood would raise water much higher than they thought.

Late last year in documents TVA filed with the NRC, engineers said new calculations show flooding would rise more than 4 feet higher than Watts Bar was licensed and designed to handle and nearly two and a half feet higher at Sequoyah than that plant was designed and licensed to handle.

NRC began publicly questioning TVA about its precautions in 2012, and in December NRC scheduled meetings with TVA officials for discussions of how the plants would fare during a probable maximum flood.

TVA assured the NRC it had the capability to monitor weather and implement a “27-hour-margin” plan to close any gaps in the sand and crushed stone baskets erected alongside the flanks of the dams several years ago at Fort Loudon, Tellico, Cherokee and Watts Bar dams to prepare for such a flood. All of those dams are upstream of Sequoyah Nuclear Plant and Chattanooga.

The large baskets — all in place as temporary fixes until more permanent options come along — have gaps if a road passes over the earthen flank.

NRC told TVA to test its margin plan. The utility did, twice.

The first test failed and TVA’s effort took several hours longer. In the second test, TVA beat the deadline by a couple of hours, Bradley said.

TVA also tested plant doors and seals at Sequoyah and Watts Bar, and found some wanting — a report NRC also heard in December. Some seals failed, meaning critical cooling equipment would have failed had there been a real monster flood.

On Monday, NRC spokesman Roger Hannah said TVA now will tell NRC how they will respond to the notices and there will be a hearing scheduled.

“Our inspectors found that their [TVA’s] strategies were not adequate,” Hannah said.



Leave a Reply

You must be logged in to post a comment.