A 30-year-old worker died Wednesday from the severe injuries he sustained in a nuclear power plant accident in Fukui Prefecture on Aug. 9, local police said.

The death of Masaru Kameiwa, who suffered burns to about 80 percent of his body from superheated steam, brings the accident-related death toll to five.

Kameiwa had been in critical condition at Fukui University Hospital.

Another worker remains in serious condition.

The accident at Kansai Electric Power Co.'s Mihama Nuclear Power Plant saw superheated steam burst from a ruptured coolant water pipe at the plant's No. 3 reactor. Four people died soon afterward and seven others were injured, including Kameiwa.

All of the workers in question were employees of Kiuchi Keisoku, a company that specializes in services for power and petrochemical plants.

The 11 workers were doing preparation work for regular reactor checks.

Kameiwa, who was to disassemble the valve of the pipe, was carrying materials to the site when the accident took place.

No radioactivity leakage was recorded as a result of the accident.

The accident occurred because the damaged pipe had been corroded by coolant water to a thickness of just 0.6 millimeter, compared with its original thickness of 10 mm.

Kepco, Japan's second-largest utility, had neglected to inspect the corroded pipe since the reactor went into operation in 1976.