NHK surveyed 10 electric power companies to study the impact of suspended operations at their reactors following the 2011 Fukushima Daiichi nuclear accident.
The survey shows that an average of 22 percent of the reactor operators were inexperienced, as of the end of August.
The ratio of such workers was the highest, at about 40 percent, at the Sendai plant in Kagoshima Prefecture, southwestern Japan. One of the plant's reactors was restarted last month.
This is followed by 37 percent at the Shimane plant, 33 percent at the Ikata plant, and 30 percent at the Genkai plant, all in the country's west.
The power companies attributed the lack of experienced workers to the increasing number of workers hired after they suspended operations at their reactors.
It is said to take 10 years to become a full-fledged operator, as comprehensive knowledge and experience are needed in such fields as nuclear fuel, radiation, electricity, mechanics and chemistry.
At nuclear plants, teams of about 10 workers operate a reactor in shifts. The survey shows that 2 of these people are inexperienced.
The power companies say they are training newly hired operators at facilities simulating reactor control rooms or at their thermal power plants.
But the companies are facing difficulties educating their operators. Some officials say one reason is that they cannot use actual machines for training.