Managers of an atomic power plant in Sweden used janitors to guard the facility when the alarm system was malfunctioning, according to a critical report Thursday from the country's nuclear watchdog.

In a statement on its Web site, the Swedish Radiation Safety Authority called the incident at the Oskarshamn plant serious because the workers had no training as security guards.

In early October, managers deployed 20-25 cleaning and maintenance staff to help guard parts of the plant's perimeter, the statement said.

The workers worked in shifts for about a week and were instructed to alert security if an outer fence was being breached, because motion sensors in parts of the newly installed alarm system were not working. The surveillance cameras and other security equipment still worked.

"OKG's decision to use non-security-educated personnel violates the company's internal routines. It is particularly serious since the routine deviation has been going on for a long time," the authority said in its report.

It also criticized the plant for not documenting the decision properly, and said the incident "could be a sign of inadequate safety culture regarding the attitude to physical protection."

In a separate statement, Oskarshamn said it had taken the criticism to heart, and said it had based the decision on the fact that the inner security fences had been intact, equipped with the necessary alarm and surveillance equipment.

The Oskarshamn plant is located 210 miles south of Stockholm. It has three reactors and provides around 10 percent of Sweden's electricity.