Decommissioning Process Fuel Debris Retrieval
Investigation Subject Strategy and risk
Issue Establishing and operating comprehensive risk management policy
① Conducting comprehensive risk management
Desired state and reasons for it
To ensure safe fuel debris retrieval, it is desirable to systematically formulate a basic risk management concept in decommissioning of the damaged reactors.
It is desirable to systematically organize the potential risks in decommissioning of the damaged reactors.
It is desirable to introduce an efficient and effective risk management method, based on the above.
Current state against ideal
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).
Issues to be resolved
Risks involving a series of decommissioning work, including fuel debris retrieval, should be identified and organized without omission. This is important to comprehensively address the risks of combustion/explosion, degradation, exposure, and dissipation/migration in the handling of fuel debris and other materials. These risks need to include both those from carrying out the work those from not carrying out the work.
It should be noted that the risk level may increase over time due to deterioration of facilities or risk sources. In addition, the risk level may temporarily increase when risk reduction measures are implemented. It is necessary to take measures to ensure that the risk level does not reach an unacceptable level by making careful preparations, by establishing a thorough management system, and by continuously advancing the system, based on an integrated evaluation of these measures.
Please note that this English text is a provisional translation of the Japanese original.