Inside buildings, there are some areas with high radiation levels where workers can be easily contaminated, but people can work safely if proper measures are taken.

Is it done by Vietnamese worker?

https://asia.nikkei.com/Economy/Vietnamese-man-surprised-to-be-driven-to-Fukushima-to-do-cleanup-work

This is like saying, people can work safely in Gaza or Afghanistan for as long as proper measures are taken.

And when they start getting various cancers a few years down the road there will be a different president of the plant saying he is not responsible for what his predecessor said or did, and that anyway there's no proof the cancers are caused by exposure at the plant. If both excuses fail, which they won't, they can just say, "Well, the person/people obvious won't working responsibly!"

The original 'nuclear gypsies' who used to do clean up work at Japan's nuclear power plants were employed through up to 8 layers of personnel dispatch companies, and when they developed cancers, were told that there were no records of them working at the plants, hence no evidence, and that as they were not directly employed by the utilities, they had no responsibility towards them.

Asians and other nationals were employed to change the reactor vessel innards many years ago, as they were allowed to receive higher cumulative doses of radiation than Japanese workers, and despite numerous accounts and evidence of them working there, their employer at the time (H) to this day denies it ever occurred.

TEPCO has done a good job cleaning up the nuclear disaster site reducing the radiation levels with workers able to wear less restrictive clothing. However, there are many areas near the reactor buildings with very high levels of prohibitive radiation.

Previously the "nuclear gypsies" at nuclear power plants did not replace nuclear fuels or work on the reactors. That work was always done by nuclear engineers.

Workers at the plant should always have radiation concerns and yearly health checks.