To prepare against the risk of internal intake of alpha- and beta-emitting nuclides, it is required to build a comprehensive internal exposure dose assessment system using bioassays and in vitro measurement (including lung monitoring). The current bioassays are time-consuming in analysis. Also, in decommissioning work, it is necessary to monitor many workers for a variety of nuclides. Therefore, Government-led R&D Program on Decommissioning and Contaminated Water Management "Development of Safety System (Technology Development of Analytical Methods for Assessing Exposure Doses)" is underway.

In accordance with the Mid- to Long-term Roadmap and TEPCO's Mid-and-Long-Term Decommissioning Action Plan, removal of interfering materials and dose reduction inside the reactor building are underway to improve the work environment in the work area and access routes.

As part of preparations for the test retrieval, on-site dose reduction work is underway and the dose in the corridor on the west side of the first floor of the Unit 2 reactor building and around the X-6 penetration in the northwest area has been reduced to approximately 5 mSv/h or less (average 2 to 3 mSv/h or so).

Regarding internal exposure protection, taking other measures on the facility such as controlling the dispersion of radioactive dust and preventing contamination spread, appropriate protection measures should be selected based on the target nuclide, airborne concentration, and surface density in the work area and efforts should be made to prevent inhalation intake and physical contamination leading to internal exposure. When an internal uptake event occurs, it is necessary to properly evaluate the deposited effective dose by in vitro measurement methods (lung monitors) and bioassay methods. Therefore, it is important to select significant alpha nuclides in the exposure assessment in advance and reflect them in the control of airborne concentrations, wearing standards for protection equipment, and equipment calibration control.

In addition, control of surface density in the work environment and the bodies of workers entering and exiting the area is important for early detection of the spread of contamination beyond the classified area and for preventing internal uptake by dust resuspended from free contaminants. Considering these, research and development started in FY2021 under Government-led R&D Program on Decommissioning, Contaminated Water and Treated Water Management for internal uptake protection and dose assessment at the time of uptake.

To reduce exposure in long-term decommissioning, it is important to accumulate experience and knowledge such as lessons learned at the on-site work and pass on know-how. In order to further expand the scale of retrieval, it is necessary to share information on handling techniques for alpha nuclides in the test retrieval and promptly provide feedback to the next work plan. Since May 2021, guidance from JAEA, which has relevant know-how, has started for the test retrieval because there are concerns about the risk of physical contamination and internal exposure in the work of handling alpha nuclides.