HARRISBURG - Radiation monitors sounded last night and again this morning inside Three Mile Island's Unit 1 containment building - the site of a small contamination incident just days earlier - but Exelon officials said they were false alarms.

Although tests showed that no abnormal radiation levels existed, Gov. Rendell today again blasted Exelon Corp. for failing to immediately inform state emergency management officials.

Rendell said the company didn't notify the Pennsylvania Emergency Management Agency until about 9:30 a.m. today - nearly 13 hours after the first alarm.

"What Exelon folks, at least the Exelon folks at TMI are not understanding is that the people of Central Pennsylvania, even though this is 30 years old, understandably are very apprehensive and jumpy about all this and there is no appropriate reason for us not to be notified about this," Rendell told reporters referring to the partial meltdown that occurred in 1979 at the plant's Unit 2.

Rendell said that all TMI officials had to do was pick up a phone, call PEMA and say "hey this is a false alarm . . . and we will get back to you as soon as we know that."

About 150 people stationed at Unit 1's containment building were sent home Saturday afternoon after monitors detected radiation contamination. Yesterday, the company said all the workers had returned to work and things at Unit 1 had retuned to normal.

No radiation had escaped from the building and the public was not endangered, according to the company and federal inspectors.

The unit has been shut down since late last month for refueling and to install new generators. Company officials said yesterday that the ventilation system had caused radiation to be blown into the containment building and that the system has since been modified.

More than five hours had passed before state officials were made aware of the Saturday incident. Rendell yesterday sent a strongly worded letter to John Rowe, Exelon's CEO, critical of the delay.

The first monitor sounded at 8:45 p.m. last night and another one on a different floor went off at 5:04 this morning, the company said.

In both cases, workers were told to leave the area as crews took air samples. Those tests indicated there was no abnormal radiation present, said Beth Archer, an Exelon spokeswoman.

She said the false alarms likely were produced by fluctuations in naturally occurring radon levels in the building.

"We value the governor's view on this issue and that's why we are committed to sitting down with [state] and local officials to review lessons learned and to ensure we have open lines of communication," said Archer.

The U.S. Nuclear Regulatory Commission said today that it is reviewing the cause of the alarms.

"It is not uncommon for radiation alarms to sound when work is being conducted in high-radiation areas of nuclear power plants," said Neil Sheehan, an NRC spokesman.

Contact staff writer Mario F. Cattabiani at 717-787-5990 or mcattabiani@phillynews.com.