KNOXVILLE, Tenn. – The Tennessee Valley Authority, faced with growing electricity demand and rising coal costs, asked regulators Wednesday to renew construction permits for two unfinished nuclear reactors it virtually abandoned 20 years ago.

Knoxville-based TVA, among the first to join a recent push to build new reactors around the country, hasn’t decided whether it will complete the Unit 1 and 2 reactors at the Bellefonte site near Scottsboro, Ala. But it has budgeted $10 million this year to study what would be involved.

The request is complicated by another project TVA is considering for the same site — two additional reactors for which TVA has applied for a combined construction and operating license with partner NuStart Energy Development LLC.

Nuclear Regulatory Commission spokesman Ken Clark said TVA’s environmental reviews for the new reactors assumed they would use cooling towers and other infrastructure built for the older unfinished reactors but didn’t account for the finishing of the older reactors.

Now, the NRC staff will have to decide if the old construction permits for Units 1 and 2 can be reactivated or if new permits will be required, Clark said.

TVA has made no final decision on whether to build any of the four reactors.

TVA Chief Operating Officer Bill McCollum said Wednesday the federal utility will need to add a major new power plant or reactor every five to seven years to meet growing demand. TVA supplies electricity to 8.8 million consumers in Tennessee, Mississippi, Alabama, Kentucky, Georgia, North Carolina and Virginia.

McCollum said TVA will be looking for the “best and most cost-effective methods.” TVA gets about 60 percent of its power from coal-fired power plants. Last week, TVA adopted a 20 percent rate increase — the largest in 34 years — due mainly to rising coal and natural gas prices.

“As we look for the best choice for new baseload generation we recognize that nuclear fuel costs are much more stable over the long term,” McCollum said in a statement.

Back in the 1960s and 1970s, TVA planned to build a 17-reactor system — one of the largest nuclear programs in the country. But most were scrapped because of nuclear safety concerns, rising construction costs and falling electricity demand.

In the past year, the federal utility and its partners at NuStart Energy Development LLC were among the first to apply to the NRC for a new fast-track license to build and to operate two proposed Westinghouse AP1000 pressurized-water reactors at Bellefonte. That application is pending.

Bellefonte Unit 1 was listed as 88 percent complete when work stopped in 1988, and Unit 2 was rated as 58 percent finished. But parts have been sold off, and it’s unclear how much can still be used.