A man in his 40s who worked for a week in August at Tokyo Electric Power Co.'s radiation-leaking Fukushima No. 1 nuclear plant has died of acute leukemia, but it was not caused by exposure to fallout, Tepco said Tuesday.

The man, whose name Tepco withheld to protect his privacy, had external radiation exposure of 0.5 millisieverts and his internal exposure was zero, Tepco spokesman Taiichi Okazaki said. A doctor who diagnosed the man said the leukemia was not caused by radiation, Okazaki added.

The man's exposure dosage was smaller than 5 millisieverts or higher per year — the benchmark for recognizing a death as work-related — Tepco said, citing the Health, Labor and Welfare Ministry's criteria on work-related deaths.

The ministry's criteria also put the incubation period to develop symptoms of acute leukemia at one year.

The man's job was to open and close doors of a worker rest area in early August, Okazaki said.

His job was to make sure radiation did not enter the rest place, the spokesman added.

The man's employer, a subcontractor of Tepco, notified the utility on Aug. 16 that he complained of sickness after working at the plant, saw a doctor and died, Okazaki said.

A health check conducted before he worked at the plant found no problems with the man, he said.

Tepco does not know the man's career history, but an official at the utility said there is no need for further investigation.

Information from Kyodo added