Reactor imaging technology for fuel debris detection bycosmic ray muon
Measurement status report in Unit-1
March 19, 2015

Tokyo Electric Power Company

本資料の内容においては、技術研究組合国際廃炉研究開発機構（IRID）の成果を活用しております。

1. Introduction
Fluoroscope technology development using cosmic ray muon
is under progress by IRID and HIGH ENERGY ACCELERATOR RESEARCHORGANIZATION (KEK) as part of subsidized project of Agency for Natural Resources andEnergy related to “FY2015 Decommissioning / Contaminated Water Management subsidy”
On 12 February, the data measurement began after detector installing process completed (suchas power reception and cable connection to the detector)
Since then, the data had been accumulated until 10 March (altogether 26 days ) and analyzed as
first evaluation.
 The information is released in this report since sufficient data was collected at reactor core area
located at the center of the observation view where huge amount of data was accumulated.
<Measurement Result>
Currently, large lumps of fuel (measuring more than 1m) have not been confirmed at thereactor core where the fuel used to be located. This result is basically consistent with TEPCO’spreviously announced estimation of the reactor and the containment vessel conditions.
The result measured this time will become very relevant information in order to grasp the debris
location to proceed with the decommissioning operation.
After the result which indicates that the melted fuel moved downward, the plan is to conduct
the investigation of the lower part of containment vessel, and identify the distribution status offuel debris remaining in the lower part of reactor by using robots. Those results obtained by theinvestigations above will be reflected in the debris removal plan.

12. Completion of Muon detector system installation
 The work began
N 9 February and

タービン建屋

Was completed 12 February. Detector-1 wasinstalled at north-west side and Detector-2 wasinstalled at north side of reactor building

設置予定位置Detector -2（North）
Reactor building
原子炉建屋

Detector -1（NW）

 A day after the measurement began, system

Coverbuilding
カバー建屋

confirmation was made on 13 February. Muon rays weremeasured stably by each detector.
 The effect of gamma rays to the data was almostnone. The value at the installation decreased by halfsince the beginning of the project (0.4=>0.2mSv/h)

Confirmation that the detector works without trouble
23. Density-length image from Detector-1 (Image created based on thereactor design drawing )Density-length image from Detector-1 based on design drawing
When the density of substances existing inside is higher, the more muon are absorbed. The Black part inside the reactor shows
reactor core location. (Assuming fuel is not damaged)
Density-length is the multiplying structure density and length along with incidence pathfrom the detector, which represents the extent of muon attenuation

34. Measurement result of the 26 days-data by detector-1 ,2Some structure and equipment edges weredistinguished, although the data shown were
not so detailed as that created by designdrawing

ター

N

Photo 1: Taken by detector-2 (North side)
Detector-2
設置予定位置（North side）

Detector-1（NW side）

Reactor Bldg.
原子炉建屋

Photo 2 : Taken by detector-1 (NW side)45. Interpretation of measured result by detector-1
Compare the measured result with actual structure and equipment layout of Unit 1

Isolation
Condenser tankDensity-length image
based on design drawing

Fuel Pool
North side
Wall of Reactor
Reactor pressure
vessel andshielding wall (RPV)
Primary containment vessel (PCV)

Photo : Measurement result taken by detector-1 and the interpretation
Structure edge can be identified clearly,
however high-density lump can not be distinguished inside RPV5

6. Qualitative estimation of debris existenceby comparing image with design drawing (detector-1)

66. Estimated position of debris by comparing design drawings withmeasured image (detector-1)
PCV boundary

RPV boundary

Reactor Coreboundary

Although the image of the measurement data is not
so clear, it shows that the PCV, the PRV and thecore are in positions where they should be.
In addition, the boundaries of the PCV and RPV on
the design drawings match those on themeasurement data.
However, the measurement data do not show theexistence of high-density substances (fuels) in theoriginal position of the reactor core.

77．Results of twenty-six day measurement with detectors 1 and 2
The results gained from the detector 1 (NorthWest side) do not identify fuel debris inside
the reactor, while those from the detector 2(North side) appear to show something exists
inside.

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Figure 1. Measured image from the detector 2 (North side)

設置予定位置Detector 2 (north side)
Detector 1(north west side)

Reactor building
原子炉建屋

Figure 2. Measured image from the detector 1 (North west side)88. Reconstruction method for 3D images of high attenuation material position

CS系
CS

Feed water
給水系
systemIn principle, permeation method can only provide 2D images. The use of two detectors, however, makes thereconstruction to create 3D images possible by combining the data from the two different angles and finding
the intersections of the cosmic rays traveling to high attenuation materials .
The position of the black objects on the data measured by the detector 2 (north side)
will be estimated by three-dimentionally assessing them.
99.3D evaluation of position of high attenuation materials in cross sections
Intersection points by both detectors
Indication points by only one detector（No existence of high attenuation materials)

SFPDS pitReactor

Cross sectionof Operation floor

Figure 4. Evaluation of the cross sectionof the operating floor
No intersections (some noise detected)

SFP
Spent Fuel
Cross section
Of SFP floor

Cross sectionof coreCS
CS系

Figure 3. Evaluation of the crosssection of the SFP floor
Some intersections （South side ofBldg, Corresponding to SFP）

Feed water

給水系
systemFigure 2. Evaluation of the cross sectionof the core
No intersections
Figure 1. Reactor Building layout (above: the operation floor on 5th floor, below: cross sections

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10．Summary
 Estimation results based on 26-day measurement data with the use of the detectors 1 and 2
High attenuation materials except fuel debris, such as the PCV wall, the R/B wall and the Reactor
Core Isolation Cooling Condenser, have been identified.
On the other hand, current data shows no large fuel debris of more than 1m in the original coreposition.
There is a strong possibility that there is no water accumulated in the core area of RPV.
(Reference: it was assumed through the water level gage calibration in May of 2011 that there was
no water accumulated in the core area.)Through the 3D evaluation, it has been estimated that there is fuel debris in the SFP. (How big they
are will be calculated later.) These results agree with the TEPCO’s estimation of the current core and PCV status.
 TEPCO will continue the measurement until it gains enough data to conduct the statistical analysis. To
make it happen, it will ask for continued support from its cooperative third parties as well as the site.
 The estimation results this time are important to locate where fuel debris inside the PCV is. Knowing
the location is essential for the steady decommissioning work.
 Given that the data gained from the measurement this time implied that a lot of debris have melted andfallen, TEPCO will start investigating the lower parts of the PCV to map the debris byemploying robots. Taking into consideration the results of various investigations into the inside of thePCV, TEPCO will work out plans to remove the debris.
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Ref: Investigation of the interior of reactor containment vessel in unit 1【Investigation area】: Underground floor pedestal (Outside)【Investigation and equipment development steps】
Proceed with the investigation from B1→B2→B3 in turn from outside pedestal(1)Investigation from reachable distance X-100B(Φ100mm)① Planned investigation on grating at ground floor outside pedestal (to determine whether CRD rail can be used ) ：B1（Plannedfor around April, 2015.4）② Specific investigation of screen image obtained at underground floor outside pedestal and operator entrance：B2（Planned for FY
2015-16）(2) Investigation from X-6①Install debris formation measuring apparatus for further recognition.：B3 (Planned for FY 2016-2017)
B1．Investigation on the surface of grating on the firstfloor except for the area of the pedestal （Around April
2015 planned to start) ：use of X-100B pipe

B2．Investigation on the condition of the underground floor and theentrance/exit for workers except for the area of the pedestal（During FY2015-FY2016 planned to start）： X-100B pipe

X-100B pipe
Opening of gratingon the1st floor

B3. Investigation on the condition of theunderground floor and the entrance/exit forworkers except for the area of the pedestal（During FY2016-FY2017 planned to start） ：use of X-6 pipe (debris detection devices installed)

X-6 pipe

Photo of the exterior ofB1 device
The process of the operations and the way of theinvestigation may change depending on the site
environment and the progress status of thedevelopment of the equipment.

The decision on whether the B3
investigation will be carried out depends
on the results of B2 investigation.

Entrance/exit for workers

Planning the investigation into the inside of thepedestal after the one into Unit 212