１. Unit 3 internal investigation (using underwater ROV)
STEP 1. Removal of monitoring instrument
STEP 3. Reinstallation of monitoring instrument
STEP 2. Investigation by underwater ROV
Separation valve
Underwater ROV Long shot camera Guide pipe for
investigation Pressured nitrogen
Monitoring instrument PCV
X-53penetration
1 Completed on July 11.
＜Reference＞
July 13, 2017 Tokyo Electric Power Company Holdings, Inc
２. Investigation plan
2
It is estimated that melted fuel had partially fallen inside the pedestal according to the analysis result. Therefore, there is a possibility of damage inside the pedestal including dropped grating and cut TIP guide pipe.
Investigation will be carried out across multiple days. First, conditions inside the
pedestal is to be checked, and review the necessity of modifying the priority order of investigation. After that, investigation restarts based on the review.
Scheduled date Contents
19 1st day of investigation: Conditions inside the pedestal are shot.
20 Necessity of modifying the plan is reviewed based on the shot image*
21 2nd day of investigation:
Investigation is conducted based on the review.
＊︓Underwater ROV is mooring around X-53 penetration during the review.
3
3. Installation method of guide pipe
The below figure shows that the double O-rings shielding gas and pressured
nitrogen forming the boundary will prevent the gas inside PCV from leaking and impacting ambient environment.
The dust concentration will be monitored during the investigation to confirm that there is no leaked gas and no impact on ambient environment.
︓Boundary
Pressured nitrogen Cable winding
drum
Cable feeding chamber
Valve O ring Separation valve (open)
Underwater Long shot ROV
camera
Guide pipe O ring
Front seal
【Plan】: ① Pedestal basement where fuel debris may exist in is to be investigated.
② Information (conditions of X-6 and CRD rail) is to be gathered to feed back into design and development of next investigation.
4 Control rod drive (CRD)
replacement rail Pedestal opening
Platform
Control rod drive (CRD) housing
Opening (slot) PCV penetration pipe
（X-6 penetration）
Basement PCV penetration pipe
used for investigation
（X-53 penetration）
Underwater ROV
Outline view of investigation
Access entrance for workers
︓investigation area
