Leaked tritium--a radioactive by-product of nuclear reaction that can cause cancer and birth defects--was found Saturday during routine tests at the Grundy County plant, according to the U.S. Nuclear Regulatory Commission.
But the company hasn't found the cause or source of the leak, which was discovered in a monitoring well and storm sewers at the 37-year-old plant, the oldest privately-financed nuclear reactor in the United States and not far from the Kankakee and Des Plaines Rivers.
Workers Tuesday were digging in the "general area" where a waste pipe is believed to have failed and are testing other wells at the plant, Exelon spokeswoman Krista Lopykinski said.
"There's no danger to public or staff safety," she said.
Records show Exelon officials took steps to hide radioactive tritium spills which escaped its Braidwood Generation Station in Will County between 1996 and 2003. It agreed to pay $11.5 million toward a new water supply for the neighboring village of Godley and is now required to inform state and federal officials of tritium spills as soon as they are discovered.
Nuclear Regulatory Commission spokeswoman Viktoria Mitlyng said the latest Dresden leak was "completely different" from the Braidwood leaks because it is limited to the plant site. Federal and state monitors are overseeing Exelon's clean-up effort and the firm is not expected to be fined, Mitlyng said.
But Paul Gunther, of anti-nuclear campaign group Beyond Nuclear, said Exelon has a history of "trivializing uncontrolled and unmonitored" tritium leaks.
"Where is that contaminated water going to be 10 years from now?," Gunther said. "Groundwater can move and its movement is hard to predict."
With a radioactive half-life of 12 years, the leak will pose a toxic hazard for 120 years, increasing the cost of decommissioning the site when the plant eventually closes, Gunther added.
Campaigners say Exelon should be more proactive in replacing aging underground pipes at Dresden, and rely less on monitoring wells to detect leaks after they've happened.
The level of leaked tritium detected in the monitoring well Saturday was 3.2 million picocuries per liter of water, more than three times what the Nuclear Regulatory Commission defines as safe for drinking water.
(The Chicago Tribune contributed to this story)
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