The Tennessee Valley Authority activated the lowest of four emergency notifications Wednesday afternoon when high radiation levels were detected in a main steamline at the newest reactor at the Browns Ferry Nuclear Power Plant in Alabama.

TVA detected the high radiation condition around 3:35 p.m., central daylight time, on Wednesday. But the notice of an unusual event was cleared almost immediately. TVA spokesman Jim Hopson said the high radiation levels were quickly lowered to acceptable levels and there was no risk of radiation exposure or other safety problems to the public or plant workers.

TVA lowered the power in the Unit 3 reactor, which was reactivated after a fuel reloading two weeks ago, to about 92 percent power while workers checked for potential problems.

The notice of an unusual event is the lowest of the four emergency notices to the U.S. Nuclear Regulatory Commission, which regulates America's commercial nuclear power plants. TVA

"Browns Ferry Unit 3 reported that the high radiation conditions were due to resin intrusion from the condensate demineralizers into the reactor and hydrogen water chemistry was a potential contributor to the event," the NRC said in its report of the incident. "The cause is still under investigation."

The unit is one of three at Browns Ferry, TVA's biggest and oldest nuclear plant located near Athens, Ala. All three reactors are now operating at full power, Hopson said.