Status of Preparations for the Unit 2 Primary Containment Vessel Internal Investigation

December 27, 2018

Tokyo Electric Power Company Holdings, Inc.

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1 Results of PCV internal investigation implemented in January, 2018

Image source and rendering: International Research Institute for Nuclear Decommissioning (IRID)

During the PCV internal investigation implemented in January 2018, the investigation unit was lowered from the area above the missing grating to examine the bottom of the pedestal. It was found that the existing structures show no major deformity or damage and that pebble and clay-like deposits cover the entire bottom of the pedestal.

When viewing the area left of center of the pedestal from the location where the camera was lowered, fallen objects, such as parts of a fuel assembly (top tie plate), could be seen in the vicinity and the height of deposits in this area was higher than that in the surrounding area. Therefore, it is possible that the area directly above this location marks one of the paths by which fuel debris fell.

Piece of fallen grating①（Seen during January 2017 investigation）

CRDreplacer elevator

Puddle

Puddle

Side of cable tray Worker access opening

Resting place of fallen pipe-like object

Resting position of fallen spring-like objects

Resting place of fallen rod-like object

Area where deposits are relatively high (Directly below fallen platform grating ①）

Resting position of fallen top tie plate（Near pedestal inner wall)Camera direction

Telescopic investigation device

Investigation unit

Pedestal

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２ Overview of the PCV Internal Investigation to be implemented

Scope of the PCV internal investigation to be implemented this time

ＲＰＶ

Containment vessel penetration pipe to be used (X-6 penetration)

Primary Containment Vessel(PCV)

Control Rod Drive (CRD) replacement rail

Pedestal opening

Pedestal

Platform

Control Rod Drive mechanism (CRD) housing

Scope of this investigation

Worker access opening

Approx. 7.2m

Subfloor

Point where investigation unit will be lowered

Since the nature (hardness, frailty, etc.) of the deposits observed at the bottom of the Unit 2 pedestal is unknown, it is important to ascertain in advance whether or not these deposits can be removed by grasping them.

During this investigation the investigation unit will be lowered from the same location it was lowered to the bottom of the pedestal during the January 2018 investigation to touch the deposits at the bottom of the pedestal and observe its behavior.

Image source and rendering: International Research Institute for Nuclear Decommissioning (IRID)

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３ Investigation method（1/2）

Concept diagram of Unit 2 PCV internal investigation using the guide pipe

Platform

Isolation valve Pedestal

Control Rod Drive

PCV penetration pipe

(X-6 penetration)

Extendable concentriccylinders with differentdiameters (extendable pipe)

Tip bend control unit Guide pipe

（Φ110mm）

PCV

Cable

Alternative shield

Investigation unit to be used this time

Investigation unit used in January, 2018

Modified

Cable drum

After the investigation device reaches the area above the missing grating, the investigation unit will be lowered to touch deposits under the platform and observe its behavior. Photographs, videos and dose data will be taken before touching the deposits and saved as information used to examine the accident.

The investigation unit used in January, 2018 will be modified so that a finger-like mechanism can be actuated to subject the deposits to mechanical force and observe the behavior of the deposits.

As with prior PCV internal investigations, the concentration of radioactive substances in dust will be monitored during the investigation using dust monitors to confirm that gasses from inside the PCV are not leaking out and impacting the external environment.

Image source and rendering: International Research Institute for Nuclear Decommissioning (IRID)

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３ Investigation method（2/2）

As with the PCV internal investigation conducted in January～February, 2017, a boundary will be formed as shown below by sealing the sliding part of the guide pipe with double O-rings and pressurizing the pipe with nitrogen to prevent gas inside PCV from leaking outside and affecting the surrounding environment during the investigation. A similar boundary will be formed for the sliding part of the cable as well.

Platform

Isolation valve Pedestal

Control Rod Drive

Tip bend control unit Guide pipe

（Φ110mm）

PCV

Cable drum

Sliding part of guide pipe is sealed with O-rings

Isolation valve (open)

Boundary

Pressured nitrogen

Inside of PCV

Pre

ssure

d

nitro

gen

Overview of sealing the cable sliding part

Sliding part of cable is sealed with O-rings

Cable

Investigation unit

Shield

Clamp

Alternative shield

Alternative shield

PCV penetration pipe

(X-6 penetration)

Extendable concentriccylinders with differentdiameters (extendable pipe)

Investigation unit to be used this time

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４ Modification of the investigation unit

The cameras and lights on the end of the investigation unit have been modified, and the unit has been equipped with a finger-like mechanism.

After the finger mechanism is allowed to come in contact with the deposits, the fingers will be actuated to subject the deposits to mechanical force and observe the behavior of the deposits.

Investigation unit used in January, 2018

Modified

Appearance of the investigation unit

CameraLight

Dosimeter, Temperature gauge

Skirt to prevent foreign material intrusion/snagging

Camera

Light Light

Finger

Skirt to prevent foreign material intrusion/snagging Dosimeter,

Temperature gauge

Direction alteredby spinning

Opens/closes after coming in contact with deposits

※The scope of the area that can be accessed is shown in the video shot in January, 2018 and may be changed depending upon actual conditions. 6

Bottom of pedestal

垂直断面図

Extendable pipe

CRD housing

Fallen grating

CRD rail

Investigation location

CRD replacement mechanism

Platform

５ PCV internal investigation location

Pedestal center

Planned investigation location※

Investigation location (taken in January, 2018)

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Work item

2019

January February March

Preparation

PCV internal investigation

PCV internal investigation

６ Planned schedule

Training

Investigation device brought in and installed

Training will begin in January, 2019. After that the investigation device will be brought onsite and installed.

The PCV internal investigation will be conducted from the middle to the end of February, 2019. The investigation is scheduled to take one day, and the date will be determined based on work progress at the site.

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CRD rail

Area A

Area B

Area A：Inaccessible because the extendable pipe touches the pedestal wall

Area B：Inaccessible due to the shape of the opening left by the fallen grating

Part A

Part B

Pedestal center

Scope of access at the bottom of the pedestal during this investigation

(reflected in the video shot in January, 2018)

Result of investigation in area B (taken in January, 2017)

Pedestal center

Investigation location

Reference: Results from deliberating the scope of access

Area B

Positional relationship of CRD rail and fallen grating