BROWNVILLE, Neb. (AP) – Utility crews extinguished a fire at a nuclear power plant in southeast Nebraska over the weekend.  The Nebraska Public Power District says the fire was discovered in the basement of the facility around 9 a.m. Saturday while crews were investigating a hazardous gas.  It was extinguished before 10 a.m.  The utility says the fire never threatened public safety.  NPPD and the Nuclear Regulatory Commission will investigate what started the fire and evaluate the utility’s response.  The Cooper nuclear plant continued operating throughout the incident on Saturday.  Cooper sits along the Missouri River in southeast Nebraska near Brownville about 80 miles south of Omaha and across the river from Iowa.