Mid-and-Long-Term Roadmap uses three basic categories for addressing these risk sources: (1) those with relatively high risk and high priority (water in buildings and fuel in pools), (2) those that are unlikely to pose an immediate risk but could increase the risk if addressed too quickly (fuel debris), and (3) those that are unlikely to pose a significant risk in the future but should be addressed appropriately in the decommissioning process (solid waste such as decontamination equipment sludge), and taking the most appropriate measures against such risk sources with priority.

The decommissioning of the Fukushima Daiichi Nuclear Power Plant is a project with a great deal of inherent uncertainty. To date, although it can be estimated the inside of the PCVs of Units 1,2 and 3 to some extent by simulating the accident progression process, estimating the location of fuel debris by muon measurement, deploying survey equipment inside the PCVs, and measuring radiation doses and taking visual images inside the buildings, there is still a large degree of uncertainty.

To resolve this uncertainty requires a great deal of resources, especially a great deal of time, but in order to achieve rapid risk reduction, it is necessary to proceed with decommissioning work in a flexible and prompt manner, even if some degree of uncertainty exists, by making use of past experience, knowledge, simulations by experiments and analyses, etc., with the highest priority on ensuring safety as well as by determining the direction.

In making such a comprehensive decision, the NDF has organized five basic concepts (safe, certain, rational, prompt, and site-oriented).