BROWNVILLE, Neb. (AP) — Federal regulators will inspect Cooper nuclear power plant next week to determine why a key heat-removal system and its backup were both offline at the same time last month.

The Nuclear Regulatory Commission says it will conduct a special inspection at the plant owned by the Nebraska Public Power District to determine what led to the error.

Regulators say that on Feb. 5 workers discovered a problem with a system that would help remove heat from the plant during an accident. That system may have been offline for months.

During the time that system was disabled, workers did maintenance work on a back-up heat-removal system, and it was offline for about 72 hours.

Cooper sits along the Missouri River in southeast Nebraska near Brownville about 80 miles south of Omaha.