Takayuki Ueno searches for missing people inside the exclusion zone in Okuma, near Tokyo Electric Power Co's (TEPCO) tsunami-crippled Fukushima Daiichi nuclear power plant, Fukushima Prefecture, Japan, Feb 14, 2016. [Photo/Agencies]

Takayuki Ueno did not hesitate one moment to expose himself to high radiation five years ago while searching for family members swept away by the tsunami that triggered meltdowns at the Fukushima nuclear plant.

The bodies of his mother and daughter Erika were found. But Ueno braves radiation and bitter cold on beaches near the crippled plant to look for the remains of his father and son Kotaro, then three years old, to bring closure to his loss.

"My highest duty as a parent was to protect my children, which I failed to fulfill. That makes me the worst parent, and I have to apologise to them," Ueno, 43, said.