TMI RESPONDS TO MONITORING WELL SAMPLE

(The following is a reformatted version of a press release issued by Exelon Corporation and received via electronic mail. The release was confirmed by the sender.)

TMI Responds to Monitoring Well Sample

Londonderry Twp., PA- (July 25, 2012) Chemistry technicians at Three Mile Island Nuclear Generating Station have found a slightly elevated level of tritium in one monitoring well on the site near the plant structure. This level is contained onsite, poses no health or safety risks, and is located in an area where groundwater is re-circulated back into the plant. The monitoring well is one of 55 on the island that samples groundwater. All groundwater in the area of the monitoring well is captured by industrial wells that pump the water back into the plant where it is used for non-potable purposes throughout the facility.

The slightly elevated level was identified in a monitoring well sample and confirmed by an independent laboratory. Subsequent samples show declining concentrations. Tritiated water at Three Mile Island is stored in tanks and carried by pipes. A team of technical and environmental experts is working to track down the source.

“TMI’s groundwater monitoring program is very comprehensive and it worked exactly as intended,” said Rick Libra, TMI Site Vice President. “We identified this one sample quickly and we’re working hard to find the source and keep our stakeholders informed.”

Three Mile Island has a comprehensive radiological monitoring program that includes 55 wells and five additional sampling stations. No unusual levels of tritium have been found in the other wells or stations.

Local and state officials and the NRC have been notified. Tritium occurs naturally in the environment, can be found at very low levels in nearly all water sources and is among the weakest of all radionuclides. It is produced in greater concentrations in commercial nuclear reactors and is monitored carefully under industrywide programs. Tritium eventually breaks down into helium, the same gas used to fill balloons.

Exelon Corporation (NYSE:EXC) is the nation’s leading competitive energy provider. Headquartered in Chicago, Exelon has operations and business activities in 47 states, the District of Columbia and Canada. Exelon is the largest competitive U.S. power generator, with approximately 35,000 megawatts of owned capacity comprising one of the nation’s cleanest and lowest-cost power generation fleets. The company’s Constellation business unit provides energy products and services to approximately 100,000 business and public sector customers and approximately 1 million residential customers. Exelon’s utilities deliver electricity and natural gas to approximately 6.6 million customers in central Maryland (BGE), northern Illinois (ComEd) and southeastern Pennsylvania (PECO). Learn more at: www.exeloncorp.com.

Contact: Ralph DeSantis Three Mile Island 717-580-0626 (mobile) 717-948-8930 (office) Ralph.DeSantis@exeloncorp.com

(bjh) NY

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