Tokyo Electric Power Co. underestimated internal radiation doses of 142 individuals who worked at its Fukushima No. 1 nuclear power plant immediately after the triple meltdown three years ago, according to the health ministry.

Also on March 25, the ministry said it instructed TEPCO to strictly monitor the health of workers according to established procedure.

The ministry said it revised the workers’ radiation exposure records upward by an average of 5.86 millisieverts.

In one exceptional case, the radiation dose was amended by an additional 89.83 millisieverts, from 90.27 millisieverts to 180.10 millisieverts, exceeding the government-set limit of 100 millisieverts over five years.

The TEPCO employee continued to work at nuclear facilities because the utility believed the person’s radiation dose was well under the limit, according to ministry officials.

The health ministry also said an additional two individuals exceeded the legal annual limit of 50 millisieverts due to the new findings.

Twenty-four of the 142 individuals whose records were revised upward were TEPCO employees. The other 118 were contractors from 18 partner firms.

The government has examined the records of 1,536 of the 7,529 employees and contractors who worked at the plant between March and April in 2011. It did so after discovering in late January that TEPCO had used inadequate methods to estimate some workers’ radiation doses while rechecking TEPCO’s health management of workers.

The utility, for example, underestimated internal doses of those who had taken iodine tablets to protect their thyroid glands from radiation exposure. It remains unclear whether and how much the agent had reduced exposure levels.