An official with Xcel Energy says a faulty pipe that allowed water containing a radioactive isotope of hydrogen to leak at a Minnesota nuclear power plant has been repaired and that the plant will return to service in the next week.

Meanwhile, a state agency says a fish kill in the Mississippi River near the Monticello Nuclear Generating Plant was caused by a water temperature change resulting from the shutdown of the plant, not by of any tritium leaking into the river.

Tritium occurs naturally in the environment and is a common by-product of nuclear plant operations. It emits a weak form of beta radiation that does not travel far and cannot penetrate human skin.