About 150 employees working inside the shut-down Three Mile Island Unit 1 containment building were sent home about 4:00 p.m. EST Saturday after an airborne radiological contamination alarm inside the reactor building sounded.
The unit has been shut down since Oct. 26 for refueling, maintenance and steam generator replacement.
No contamination was found outside of the containment building. Radiological surveys showed that the contamination was confined to surfaces inside the containment building.
The event posed no threat to public health and safety.
A monitor at the temporary opening cut into the containment building wall to allow the new steam generators to be moved inside showed a slight increase in a reading and then returned to normal. Two other monitors displayed normal readings.
"Workers were sent home because work couldn't continue until we clean the area," Exelon Vice President Bill Noll, the senior executive at TMI, said. "We hope to be able to resume activities tomorrow."
Exelon technicians Saturday night were checking employees who had been working in the building at the time for possible unusual radiation exposure. One worker was found to have received 16 millirem of exposure, and other workers have received contamination of lower levels. The annual occupational dose limit for nuclear workers at Exelon Nuclear plants is 2,000 millirem. No Nuclear Regulatory Commission limits were exceeded for personnel contamination.
Numerous work activities were going on in the building at the time the alarm sounded, and Exelon engineers are working to determine the cause the incident. The NRC, Pennsylvania Department of Environmental Protection and local elected officials were notified of the event.
Exelon Corporation is one of the nation's largest electric utilities with approximately $19 billion in annual revenues. The company has one of the industry's largest portfolios of electricity generation capacity, with a nationwide reach and strong positions in the Midwest and Mid-Atlantic. Exelon distributes electricity to approximately 5.4 million customers in northern Illinois and southeastern Pennsylvania and natural gas to approximately 485,000 customers in the Philadelphia area. Exelon is headquartered in Chicago and trades on the NYSE under the ticker EXC.