I believe this large scale study has revealed the dose response effect of irradiation to carcinogenicity in human being. It means it is advisable to minimize the irradiation dose. It is known some people are genetically rather liable to cause cancer with low dose of irradiation. From that standpoint, we should also limit the irradiation dose as low as possible.
An former worker at the accident of the Fuskushima nuclear power plant is reported to occur leukemia recently. He has been authorized as a case of compensation insurance. He has been reported to have been irradiated up to 19mSv while working at the plant. Half of 20,000 workers are reported to have received mora than 5mSv a year. There could be more patients with malignancy from this group of workers in the future.
Nuclear power plants, either in normal shape or in accident, cause much irradiation to the workers there, which could result in their serious health problems. In addition to the used nuclear fuel problem, this fact tells us to give up nuclear power energy at present. It won't be "clean" energy at all.