Exelon Corp., owner of the largest number of U.S nuclear reactors including the Oyster Creek nuclear facility 9 miles south of Toms River was sued Thursday by Illinois Attorney General Lisa Madigan over the release of radioactive wastewater from the company's Braidwood nuclear reactor.

The suit, filed in Will County Circuit Court, alleges that tritium-laced water from the plant entered groundwater used by neighboring residents. It claims six of eight releases during the last decade resulted from inadequate maintenance and operations at the plant in Braceville, Ill., about 50 miles southwest of Chicago.

Tritium is a radioactive isotope of hydrogen that in high concentrations could cause cancer.

Operations at the plant "clearly placed their profit margin first with a callous disregard for the health, safety and welfare of the local residents," Madigan said.

Exelon said it was continuing inspections at all 11 of its reactors and was discussing remediation plans with the attorney general.

"We're going to check this out at all of our sites," John Young, chief financial officer of Chicago-based Exelon, said in New York. "We are taking it very seriously."

Exelon is in the process of applying for a license renewal for Oyster Creek, the oldest commercial reactor in the country, that would keep the Ocean County plant open until 2029.

Since last year, Exelon has also operated three nuclear plants in New Jersey that are owned by Public Service Enterprise Group as part of its proposed $16.2 billion purchase of PSEG.

The takeover remains subject to state regulatory approval.