Unit 2

Status of Progress Points

(*1) Penetration: Through-hole of the PCV
(*2) SFP (Spent Fuel Pool)
(*3) RPV (Reactor Pressure Vessel)
(*4) PCV (Primary Containment Vessel)

(1) Replacement of the RPV thermometer

As the thermometer installed at the Unit 2 RPV bottom after the earthquake had broken in February 2014, it was excluded from the monitoring thermometers.
On April 17, 2014, removal of the broken thermometer failed and was suspended. Rust-stripping chemicals were injected and the broken thermometer was removed on January 2015.
A new thermometer was reinstalled on March. The thermometer has been used as a part of permanent supervisory instrumentation since April.

(2) Reinstallation of the PCV thermometer and water-level gauge

Some of the permanent supervisory instrumentation for PCV could not be installed in the planned locations due to interference with existing grating (August 2013).
The instrumentation was removed on May 2014 and new instruments were reinstalled on June 2014. The trend of added instrumentation will be monitored for approx. one month to evaluate its validity.
The measurement during the installation confirmed that the water level inside the PCV was approx. 300mm from the bottom.

Image of the torus room east-side cross-sectional investigation

The torus room walls were investigated (on the north side of the east-side walls) using equipment specially developed for that purpose (a swimming robot and a floor traveling robot).
At the east-side wall pipe penetrations (five points), “the status” and “existence of flow” were checked.
A demonstration using the above two types of underwater wall investigative equipment showed how the equipment could check the status of penetration.
Regarding Penetrations 1 - 5, the results of checking the sprayed tracer^(*5)by camera showed no flow around the penetrations. (investigation by the swimming robot)
Regarding Penetration 3, a sonar check showed no flow around the penetrations. (investigation by the floor traveling robot)

(*5) Tracer: Material used to trace the fluid flow. Clay particles

Prior to fuel debris removal, an investigation inside the PCV will be conducted to inspect the status there including the location of fuel debris.

[Investigative outline]

A robot, injected from Unit 2 X-6 penetration(*1), will access the inside of the pedestal using the CRD rail.

[Progress status Status]

As manufacturing of shields necessary for dose reduction around X-6 penetration was completed, a hole was made in December 2016 at the PCV penetration from which a robot will be injected.
On January 26 and 30, 2017, a camera was inserted from the PCV penetration to inspect the status of the CRD replacement rail on which the robot will travel. On February 9, deposit on the access route of the selfpropelled investigation device was removed and on February 16, the inside of the PCV was investigated using the device.
The results of this series of investigations confirmed fallen and deformed gratings and a quantity of deposit inside the pedestal. The evaluation results of the collected information will be utilized in considering the policy for fuel debris removal.

(*1) Penetration: Through-hole of the PCV