LONDONDERRY TOWNSHIP, PA (Dec. 18, 2009) - Significant progress has been made in the completion of Three Mile Island's refueling outage. In recent days, the two new steam generators have been installed, the temporary opening in containment has been sealed and hundreds of other maintenance projects have been completed.
Refurbishment the plant's two cooling towers and the overhaul of two back-up diesel generators has been completed. Thousands of workers continue to work on-site to complete the remaining projects and prepare the plant for a return to service in early 2010.
Data analysis being completed today from two of seven remote monitors near TMI appears to validate readings taken Nov. 21 near the opening of the TMI containment building and reported at that time. The slightly above background radiation readings amount to about a third of the level a person receives from wearing a luminous wristwatch.
In the analysis, one of the monitors located about a mile from the plant showed an increase of 0.02 millirem, an amount well below any immediate reporting limit. The second monitor showed a statistically insignificant change in reading. The samples were taken between Nov. 18 and Nov. 24 and required several weeks to analyze and validate.
As reported in a Nov. 21 Exelon news release, a monitor placed at the temporary opening in the TMI containment building wall to allow the new steam generators to be moved inside showed a trace increase at that time and then returned to normal.
"These are very sensitive monitors capable of detecting extremely low levels of radiation. In this case, the amount of radiation detected is equal to about 1/18,000 of a typical person's annual background exposure from natural sources," said Craig Nesbit, vice president of communications for Exelon Generation.
The monitor findings are well below immediate regulatory notification thresholds. Exelon made courtesy notifications to local, state and federal elected and regulatory officials.
"This amount is insignificant from any health or safety perspective, but we felt it was important to let people know what we found," Nesbit said.
A millirem is a measure of radiation exposure. A typical person receives about 360 millirem of radiation annually from natural sources, such as soil and rocks, cosmic rays, food and consumer products. For example, a person living in a brick or stone house receives about seven millirem of exposure a year from radioactive elements in clay and rock. That's 350 times greater than the anomaly recorded at TMI.