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Unit 1

From April 10 to 20, 2015, a pre-investigation was conducted for the purpose of determining the locations and forms of melted fuel that has dripped down in the primary containment vessel (PCV), with robots used for the first time by being inserted into the PCV to ascertain the conditions. These robots represent the collective technology of Japan. This investigation provided us with vital information such as images, radiation doses, and temperature inside the PCV.
Inserting of robots into the PCV performed this time has been such an unprecedented challenge to the nuclear industry, and we believe that the fact that critical data was gained from the investigation demonstrates that we have made a massive leap forward, contributing greatly to our future decommissioning work. We are accumulating and aggregating the data we have obtained in this pre-investigation to use it for future decommissioning work.

* This investigation was conducted as a verification test of technology for investigating inside the Unit 1 PCV for the "Development of a technology to investigate inside the Reactor Primary Containment Vessel (PCV)" of the International Research Institute for Nuclear Decommissioning (IRID).

[Video] 2015.05.18 An unprecedented challenge Robots obtain crucial information on conditions inside the Fukushima Reactor (4:04)

Investigation Overview

Findings

Check for access routes for next investigation

No obstructions were found around the opening to access the bottom part of the PCV, which indicates that the opening can be used as an investigation route when searching for fuel debris in the future.

Ascertain temperatures and radiation doses

Data on temperature and radiation dose at each investigation point was obtained.
The level of the measured radiation dose indicated lower values compared to those originally assumed, resulting in the investigation taking longer than originally planned.

No significant damage to equipment inside PCV

It was found that there was no significant damage to the various equipment in the PCV.

Check of the grating (netting-type floor) of the 1st floor inside PCV

The inside of the PCV was checked for fallen objects and obstacles, and the condition of the grating was also checked.

Other information obtained

Both of the robots used were left inside the PCV.
It was also confirmed that the remaining cables extending out from the robots will not interfere with future investigations.

Images from the Investigation

Image from B3

Image from B4

Image from B7

Image from C2

Image from C7

Image from C10

Conditions of the grating of the 1st floor inside PCV

Data on temperature and radiation dose at each investigation point

Dose Rate(Sv/h) Temperature(°C)
B3 7.4 17.8
B4 7.5 19.2
B5 8.7 19.4
B7 7.4 19.5
B11 9.7 19.2
B14 7.0 20.2
C2 6.7 19.6
C5 8.3 19.5
C6 7.7 19.4
C9 4.7 20.8
C10 5.3 21.1
C11 6.2 20.7

Image of cables extending out from the robots remaining inside the PCV

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