Xcel Energy has found higher-than-natural levels of radioactive tritium in a monitoring well at its Monticello Nuclear Plant.
One sampling found a level of 21,300 picocuries per liter of tritium, which is slightly above the federal Environmental Protection Agency drinking water standard for tritium of 20,000 picocuries per liter.
Tritium is a radioactive form of hydrogen that occurs naturally and as a byproduct of electricity production at nuclear power plants.
Xcel recently drilled a new well near the reactor because workers detected a leak inside the building. Plant engineers believe the tritium came from a leaking valve that was repaired in May.
Workers are drawing water from near the reactor building into the well and putting it in containers. Xcel says the water will be reprocessed through normal plant systems, which do not come in contact with the environment.
Xcel says if someone consumed drinking water containing 21,300 picocuries of tritium for a year, he or she would receive an annual radiation dose of 0.97 millirem. According to the U.S. Department of Energy, dental and chest X-rays result in 25 millirems of radiation.
Xcel is applying to the Nuclear Regulatory Commission to expand production and waste storage at Monticello. The NRC recently decided a full Environmental Impact Statement is not needed, because the expansion would produce no significant environmental effects.