Japan's Kansai Electric Power Company said an accident this week at its nuclear plant that killed four workers occurred in an area that was soon to be inspected for the first time in 28 years, and months after a warning of potential problems, according to Reuters.

Four workers were killed in Japan's deadliest nuclear industry accident when super-heated steam escaped from a ruptured pipe in a building housing turbines for a reactor at the Mihama nuclear power plant, 200 miles west of Tokyo.

There was no radiation leak, but the accident raised further concerns about Japan's nuclear safety record.

"The pipe was to have been checked at an upcoming regular inspection," said a Kansai Electric official.

He said the pipe had not been checked since 1976 because it was not on an inspection list — something Kansai Electric was notified of in November by a maintenance subcontractor.