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Exelon Byron Nuclear Generating Station
On-going Tritium Investigation

Fact Sheet 1
April 2006

Byron, Illinois

Site Location Map, Exelon - Braidwood Nuclear Facility

Exelon Corporation operates the Byron Nuclear Generating Station in Ogle County.  On February 13, 2006, the Illinois Emergency Management Agency (IEMA) – Division of Nuclear Safety notified the Illinois Environmental Protection Agency (Illinois EPA or Agency) that Exelon had inspected six vacuum breaker relief valves along the three-mile long blow-down line which runs west from the station to the Rock River.  The blow-down line carries process water and wastewater from the plant and occasionally tritium.   Five of the vaults had standing water in them.  The vacuum breaker vaults, which are part of the discharge system, have weep holes on the bottom that threatened the release to groundwater of the standing water in the vaults.  No discharges down the line occurred from late January to April 20, when releases down the discharge line resumed.  The station is installing leak detection devices at each vault along the line to give immediate notification should a leak occur.  In the interim, visual inspections will occur at each vacuum breaker location during each planned release to ensure no further leakage occurs. 

Concentrations of tritium in the standing water samples from inside the vaults ranged from less than 1,000 to 82,000 picocuries per litter (pCi/L). (A picocurie is one trillionth of a curie.)  The results are from an on-site laboratory where the detection limit for tritium is 1,000 pCi/L.  By comparison, 20,000 pCi/L is the maximum contaminant level that is allowed in public drinking water by federal regulations.  The standing water in the vaults was pumped into containers, brought back on-site, and processed through their normal system.

Two days later, the Illinois EPA began evaluation of the threat to potable water wells in the area.  Exelon collected water samples from nine private water wells near the blow-down line.  No water samples contained detectable levels of tritium above a 200 pCi/L detection level. During that time, private well water samples were also collected by the Nuclear Regulatory Commission (who has jurisdiction over the radioactive contaminant discharge to surface water).  Levels of tritium were independently confirmed by that agency.

Analytical results from the private water well sampling have been submitted to the Illinois Department of Public Health for their review and letters of explanation regarding any health risks associated with tritium will be sent to property owners. 

At this time, Exelon has installed 15 shallow monitoring wells around the vacuum breaker line, only two of those had water in them, and there were no detectable concentrations above 200 pCi/L. An additional eight deep monitoring wells near the vacuum breaker valves have been installed and sampled.  Two deep monitoring wells located near vaults 3 and 4 had detectable concentrations of tritium above background, at 459 pCi/L and 3572 pCi/L, respectively.  Five additional monitoring wells have been installed around the plant itself. None of these contained detectable concentrations of tritium.  In addition, a test well near the river that was previously dry has been re-drilled deeper, and a new deeper test well has been installed near vault 4.  Samples in these wells have not contained detectable concentrations of tritium.  All six vacuum breaker vaults are now being sealed by Exelon to prevent any further release of tritium from the blow-down line. 

Conestoga-Rovers and Associates, Exelon’s consultant, will continue their environmental investigation by doing additional water sampling of  monitoring wells and evaluation of the underground piping.  In addition, the consultant is working on a risk assessment. Exelon routinely updates the Agency regarding on-going investigations. The Illinois EPA is committed to protecting the groundwater of the state as a future drinking water source.  A violation notice was issued to the Exelon Byron Nuclear Generating Station on April 12, 2006.  This notice specifically identifies violations of state environmental regulations relating to impairment of resource groundwater.  Exelon is also being cited for discharging waste-containing contaminants from areas of the discharge system other than the outfall points allowed by its NPDES (National Pollutant Discharge Elimination System) water discharge permit, as well as violating other operational and reporting requirements of its NPDES discharge permit.

The alleged violators will have 45 days from receipt of the violation notice to respond and provide an enforceable plan for addressing each of the specified violations to prevent a re-occurrence.  During that time, they may document that the charges are not applicable, or demonstrate to the Illinois EPA how they will resolve the violation through a proposed compliance commitment agreement.  The Illinois EPA would have to concur with the plan.

Additional information will be added to this web page as the environmental investigation continues.

For more information:

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Steve Johnson
Environmental Toxicologist
Illinois Department of Public Health
Rockford Regional Office

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