It is difficult to uniquely identify issues in fuel debris retrieval because it is necessary to proceed while constantly facing the unknown and flexibly reviewing the work, based on new knowledge obtained from various analyses and work experience, etc.

It is also necessary to clarify the criteria for comprehensively judging evaluation axes of different natures, such as safety level, field applicability, technical feasibility, business continuity, and throughput.

As for the utilization of the knowledge to be obtained through the test retrieval at Unit 2, it is necessary to reflect, for example, the status of existing structures and distribution of sediments, distribution of gamma radiation and neutron counts, the degree of impact on confinement caused by loading and unloading of equipment, and information on fuel debris to be collected during the retrieval in equipment design, retrieval procedures, safety assessment, etc.

In addition, it is necessary to investigate the retrieval method considering the results of the investigation of the method in the preceding Unit 3.

Although it has been evaluated that there is almost no fuel debris in the core from the survey and analysis using muons, it is not a direct , so a direct video survey is required in the future investigation.

Since not all of the fuel debris is planned to be retrieved by the side access method, it is necessary to investigate the method for further expansion of the scale of retrieval.

Considering the knowledge to be obtained through the test retrieval, it is necessary to proceed with the design, fabrication, and installation of fuel debris retrieval facilities, safety systems (confinement, fuel debris cooling, criticality control, etc.), maintenance facilities for fuel debris retrieval and storing facilities.

It is necessary to investigate the method, taking into account the possibility that some fuel may remain in the core.

Since the investigation outside the pedestal has not been conducted, a direct video survey is necessary in future investigation.

In order to increase the certainty of the selected method, it is necessary to investigate plans for surveys to understand the distribution of sediments outside the pedestal, as well as additional surveys in the pedestal and in the RPV, and to reflect the results of these surveys in the investigation and design of the method.

In investigating the method, it is necessary to investigate confinement facilities considering the damage status of the reactor building.

It is necessary to enhance the knowledge through internal investigations, etc., and to consider the events during the accident inferred from the discharge of high-temperature sediments (fuel debris) out of the pedestal. Taking these knowledges and considerations into account, it is necessary to investigate the method of retrieving sediments inside and outside the pedestal, the possibility of sediments flowing into the S/C, etc., and to reflect the knowledge obtained from the internal investigation in the fuel debris retrieval method, including those of other Units.

Since the information obtained so far about the inside the PCV of each Unit is limited and there are many areas where direct visual information has not been obtained, investigations on further surveys such as internal investigation of the PCV and RPV of each Unit should be proceeded to collect more information at an early stage, including the damage situation at the bottom of the RPV and the existence and distribution of sediments outside the pedestal.

Maintenance of remote equipment and restoration in case of failure also need to be considered. It is necessary to investigate a method considering the entire work sequence from preparation to retrieval and the throughput, and it is necessary to select a method that can be used for retrieval even if the entire site situation cannot be identified, and a method that is not affected by external events such as earthquakes (robust method).

After retrieving the fuel debris, it is necessary to investigate the criteria for shifting to building dismantling. In other words, it is important to determine to what extent fuel debris retrieval can be said to be complete and how to confirm this.