Officials at the Fukushima Dai-ichi nuclear plant said his body showed no signs of dangerous levels of radioactivity.
The man, who was in his 60s, worked in the area of the building that stores radioactive-contaminated water.
Kyodo News agency reported the man had no apparent injuries and a second worker nearby had no ill health effects.
Two Fukushima workers had died from the tsunami itself, when waves swept into the plant and heavily damaged buildings and equipment.
The quake and tsunami are believed to have killed more than 24,500 people. Police said Friday that 15,019 were dead and 9,506 were still listed as missing.
Meantime, another nuclear plant in central Japan has been shut down at the government's request.
Chubu Electric said it will build a large seawall and other safety structures at the Hamaoka nuclear plant in Shizuoka. Construction is expected to take a few years.
The Associated Press contributed to this story