Updated

The head of the utility behind Japan's nuclear crisis acknowledged Monday that hundreds of workers at the contaminated Fukushima Dai-ichi plant were mobilized through a murky hiring system.

Tokyo Electric Power Co. President Naomi Hirose attributed the hiring problem to high worker turnover at the highly contaminated worksite, adding that the problem became prevalent as the company desperately tried to recruit workers willing to take jobs with high risks of radiation exposure.

The March 11, 2011, earthquake and tsunami destroyed power and crucial cooling systems at the Fukushima plant, causing multiple meltdowns and contaminating the plant's surroundings. The plant has substantially stabilized since then, but full decommissioning is expected to take decades.

Hirose said TEPCO is working to fix the hiring problem, which he attributed to an industry-wide hierarchical contract system. But he said that the deep-rooted industry practice cannot be changed overnight, and that a full overhaul will be difficult.

"Ideally, it would be best if we reform the contract hiring system and start from there, but it will be extremely time-consuming," Hirose said. "It's a difficult task we cannot do on our own. It will take heavy-duty work. It involves history and business ties, and could even hurt the industry."

In a recent TEPCO survey of some 2,400 contract workers, dozens said they were instructed to falsify affiliations, while some complained they never received a written contract.

In the survey, taken in September and October, about half said they were being paid by different companies than the ones that hired them — an indication of illegal labor contracts. Nearly 90 percent said their employers were ranked from second to fourth in the hierarchy of subcontractors. About one-quarter said their employers never notified them of their radiation exposure details.

The hiring problem has intensified since last year's disaster, and some workers have come forward and complained that their salaries have been siphoned off or allowances not given.

Hirose said securing a workforce that can last through decades-long post-disaster operations would be critical to cleanup efforts.

"Decommissioning is a lengthy process of 30 to 40 years, which is long enough for a fresh employee to reach retirement age," he said. "Our staffing is sufficient in the short term, but we may face a difficulty in the long run."

Hirose said TEPCO hopes to invite experts from the United States, Britain and France in coming years to seek technology expertise and support to decommission Fukushima's reactors.