高さ（OP）[m]Height OP[m]

Locating Fuel Debris inside the Unit 3 Reactor Using a Muon Measurement Technology

at Fukushima Daiichi Nuclear Power Station

September 28, 2017

Tokyo Electric Power Company Holdings, Inc.

The contents of this document is what TEPCO carries out as

a part of the project developed by the International Research

Institute for Nuclear Decommissioning (IRID)

Installation of muon measuring device (small-sized unit, approx.1m×1m×1.3m(height)) Installation location of

Overview

N

 As the step of gathering information about fuel debris distribution toward a removal of fuel debris, muon measurement using a transmission method that obtains

quantitative distribution in the Reactor Pressure Vessel (RPV) from transmittance of muon particles which have passed through the reactor have been carried out in Unit 1 and 2.

 Unit 1︓No massive fuel in the core area (Feb.-May., May.-Sept., 2015)

 Unit 2︓High-density materials that is considered fuel debris at the lower area of RPV (Mar.-July., 2016)

 Unit 3 muon measurement has been carried out from May to September, 2017. The result is reported. (Measurement was completed on September 8.)

Measuring device (1 ^st floor of turbine bldg.) Reactor bldg.

N

 Muon is the secondary cosmic ray generated in the collision of cosmic ray from space with atmosphere. Muon has high energy and characteristics to pass through materials.

 By measuring muon particles which have passed through the reactor building, images of fuel debris distribution inside the RPV are captured like X-ray pictures from their transmittance.

(Higher density materials that less muon can pass through make darker shadow.)

Measurement principle of the muon transmission method

Measurement image of muon particles that pass through the reactor building

（East-west cross section）

Spent fuel

（SFP） pool

South North

Measuring device

X axis

Y axis

X axis muon

Y axis Panel① Panel②

Rough location of

the core

Reactor bldg.

Turbine bldg.

West East

Measurement principle of

the muon transmission method（image）

Two panels (plastic scintillators) inside the muon measurement device detects incoming cosmic rays muon and calculate their trace on where they have

pass through from the coordinates on the panels. Distance between the panels:

approx.50cm Measuring

device Measurement image of muon particles that pass through the reactor building

（North-south cross section）

North

South

Measuring device

West East

Result image using the muon transmission method

 By measuring muon particles which have passed through the reactor building, the reactor building is seen through.

Simulation

（without fuel）

Simulation

（with fuel）

Simulation conditions

・ Reactor core and lower area of RPV ： With fuel

・Inside SFP： Filled with water

Simulation conditions

・Reactor core and lower area of RPV： Without fuel

・Inside SFP： Filled with water

Projected image

Projected images by muon are simulated from structure map of the reactor building

 By projecting on the cross section though the reactor, images of fuel debris in the reactor core and the bottom of RPV are captured like X-ray pictures.

RPV Core area

RPV

Core area

高さ（

OP

[m]

Result of Unit 3 muon measurement (Quantitative distribution)

Quantitative distribution

（g/cc・m）

Spent fuel pool

Concrete wall surrounding PCV RPV

North South

Mountain side hill ^*

Height O P[m]

Horizontal distance[m]

 Quantitative distribution of unit 3 from measurement up to date is as the picture bellow. (The interpretation is shown on the following pages.)

Building wall （Main steam isolation valve）

Reactor Core area

（As of September 8, 2017）

Main structure in the reactor building (comparison with simulation)

Spent fuel pool

Concrete wall surrounding PCV RPV

North South

 By measuring muon particles which passed through the reactor building, main structures in the reactor building including the concrete wall surrounding PCV, the spent fuel pool and wall of building were recognized.

Quantitative distribution by simulation

（Case with fuel debris in core area and at lower

area of reactor） Quantitative distribution by muon measurement

Building wall（ Main steam isolation valve ）

Reactor core area

（As of September 8,2017）

North South

RPV

Reactor core area

Concrete wall surrounding PCV Spent fuel

pool

Building wall（ Main steam isolation valve ）

Mountain side hill

Reactor bldg.

North

Measuring device

 Quantitative distribution obtained from the muon measurement includes some effects of structures such as building wall, floor and the RPV itself.

 These effects should be taken out for the true quantitative distribution inside the RPV.

 Evaluate quantitative distribution of structures which exist front and behind of RPV by identifying design drawing and simulation in order to exclude it from

measurement result.

Evaluation of quantity inside the RPV

Reactor bldg.

Turbine bldg.

West East

Measuring device

Quantitative distribution of main constructions including building wall, floor and the RPV overlapping with the RPV relative to the measuring device is evaluated from the design drawing.

Quantitative distribution of

structures locating back and forth

of the RPV should be taken off for

the distribution inside RPV.

Inside the RPV

Inside the RPV

Quantitative distribution inside the RPV（①Core area）

 Quantity of structures such as building wall, floor and the RPV was taken off from the measurement result based on simulation.

 Status of fuel is evaluated by comparing the true distribution with simulation result for the case that the RPV is filled with a hypothetical material with uniform density.

Core area

（upper side）

Core area

（Lower side）

Analysis using Muon measurement Simulation（3g/cm ³ )

Simulation（0g/cm ³ )

・ Simulation（1g/cm ³ )

00000000- 3- 7- 5- 1 0- 1 2- 8- 1 2- 3- 50000 0000

000000- 40- 2- 7- 12- 5- 3- 3- 51- 2300 0000

00000- 1- 4- 4- 5- 7- 5- 2- 10- 1- 5- 1 00- 710 0000

0000050- 351 4- 40- 1- 11 011- 4650 0000

000038- 76- 2- 2- 151- 14- 17- 3- 2- 95 0000

000- 2- 9- 4- 1- 4- 3- 4- 10- 2- 6- 12- 8- 5- 6- 2- 3 0000

00074- 2- 4- 43- 4- 2- 51- 3303- 2- 3- 3- 7- 1 000

006- 8- 104- 310321- 3- 384- 5843- 2- 500

00- 8- 2- 3022025- 60- 50- 6121- 4- 4- 3 100

00- 1- 4- 4- 5- 70- 2- 1- 43- 2- 1162- 6- 440 4- 100

05- 4- 45- 3- 401- 48360- 224- 1103- 6 0- 40

0830550241 331 03931 24675- 1 5600

017- 2- 4340- 1 1408324585444- 7 200

05- 2- 51 86352- 1- 351 10- 3424520 4630

0- 5- 7- 4- 154- 1872241- 2404733 1320

0- 424- 553533583581 61 03721 5- 1 3- 40

0- 217- 71- 600341 11571 3- 3585- 2 0- 1- 40

0- 1- 3- 315- 24573- 1214231 1544 10- 90

071- 890376251 2- 434668560- 1 3- 30

0- 8- 6- 6- 120- 2- 44132- 32865- 121- 1- 3- 40

032- 351 3147- 251 227- 14481 355 3100

0- 1- 44431 179841 2581 04- 18165 5310

0- 4- 8- 3213355- 13- 124506171 2- 350

07- 5- 3- 23941 694522266- 6061 2- 440

01- 2- 423066515520240521- 2 460

00- 30086133604- 11204- 3- 2- 4 2100

01- 6- 2- 30576000- 254302- 51- 3 21- 10

06- 2- 3- 354533- 310- 3- 2- 201100- 4- 220

03- 4- 4056456423212- 11311- 2 040

040- 1145257643332- 10121- 2- 270

0- 3- 315763414050- 244- 1101- 3- 320

0- 10- 14271 21 00644244- 14431 1 2130

00- 5- 22664544073- 2- 112- 214 00- 40

03- 5- 261 538985965541747- 2 11- 20

01- 4- 1124422- 123- 2- 233- 2- 300- 3- 2- 40

0- 32122552263305033233 0- 1- 50

0- 2- 4- 34285443243231- 130- 1- 4- 5- 50

0- 10- 1- 701- 11- 14133- 2- 2- 1- 5- 16- 1- 7- 6- 30

0- 4- 401361- 20- 3- 1- 3- 2- 31- 3- 4- 31- 3- 5- 9- 50

03245853308- 20331- 12011- 3 0- 10

0- 21- 224- 140151- 14221312- 4- 4 - 3- 10

03- 1397831756138- 206410- 2 - 340

0- 4- 3002214413- 1- 12- 2- 20- 3- 5- 6- 7 - 320

03- 1- 13381554257070- 32- 4- 6 0110

01- 6- 1- 10655241- 130102- 1- 5- 3- 2 - 2- 10

0- 2- 31- 1651 05823553013- 1- 5- 5- 2 - 220

00304261 0663451334- 41- 3- 2- 1 - 100

01- 6- 205252856552363- 7- 30 4010

0- 2- 2- 113275564343311- 2- 10 00- 10

002- 5- 22354786553715- 316- 1 1- 20

03- 2534899632123533121 3310

01- 378451 0457544291 06184 4- 330

00425124847150523- 1101- 1 - 300

0- 6- 11- 3431 1691 15306431229 1200

0- 13632563456030210- 324- 1 - 150

025- 1- 2151461 055105- 10- 172 4120

02203- 2257630200320- 122- 1 240

0- 6- 1 2- 22- 60- 1721- 1- 34- 10- 3111- 1- 1 6- 10

0- 4- 1- 2- 1- 5- 3- 1- 4- 1- 40- 3- 3- 3- 5- 2- 4- 5- 4- 6 1- 5- 10

0- 7- 675045501423124- 1- 2- 31 0- 1- 10

0- 2- 403- 4351- 3- 10- 5- 4- 4- 20- 1- 4- 7- 4- 2 - 6- 20

0- 5 66324616351- 122352- 25 0- 580

001- 5- 1644010- 5- 4- 1- 125- 310- 4- 3 0- 20

0- 2 - 1013533750723- 13551- 2- 5- 440

05674234463531305440- 3- 5 060

06- 351 3331 01 39674- 11 275830- 9- 2 120

0226252465237764675- 4- 4- 2- 250

0- 1 1 48730- 23156- 1475646- 2- 4 2050

041033- 1181212201511- 1- 3 1050

03- 12858461364221 06630- 1- 1 370

071583453461305569310- 3 040

0101 255352500370- 3270- 5- 7- 4- 1 020

002280- 45652626426621- 4- 8 360

03- 84- 37- 3223327- 510- 11- 21- 6- 1 0- 150

001 0411- 124456322788557- 2 280

0342- 2- 21 31 31375581 161 57- 22- 2 041 00

01541- 56- 17631 001841 39- 501 6060

0- 1- 1563563- 17661 21 3- 11 073- 4- 2 0220

00- 1533- 11 1184543084811- 1- 3- 200

0- 3- 1202- 7572436- 110767- 71- 2 170

03- 314- 6057346596177413- 2- 1 040

00- 647081 6731 31 2831 01 01 383- 82- 2- 350

0- 50- 522- 1321 11 066881 01435- 5- 8- 9- 90

00- 31 0- 15571 51 2222673- 4- 403- 4 1- 400

0074- 1691 21 61 61 41 271 8600- 100- 2 2500

0093- 5- 331 71 11 71 21 21 064- 5220- 10- 5- 200

000921 141 21 1771 21 378- 6- 1- 8- 4- 13 2000

000051221 8- 51 31 100- 1 27- 414- 1 10 0000

000001 4895- 789- 761- 2- 1 1- 23- 90 0000

0000001 9993- 614- 6- 21- 27500 0000

00000001 3- 21 27- 210- 41- 65000 0000

0000000000- 21278000000 0000

Quantitative distribution inside the RPV

（inside of the inner wall）

South North small ← Quantity → large

-20 - 1 8 - 1 6 - 1 4 - 1 2 - 1 0 - 8 - 6 - 4 - 2 0 2 4 6 8 1 0 1 2 1 4 1 6 1 8 2 0

Average density of healthy core (w/o water)

is approx.3g/cm ³

 Quantity in core area is distributed in average density lower than 1g/cm ³ . Quantity greatly decreased.

（Error bar shows only random error.）

Core

Quantitative distribution inside the RPV（②RPV bottom）

00000000- 3- 7- 5- 1 0- 1 2- 8- 1 2- 3- 500000000

000000- 40- 2- 7- 12- 5- 3- 3- 51- 23000000

00000- 1- 4- 4- 5- 7- 5- 2- 10- 1- 5- 1 00- 7100000

0000050- 3 51 4- 40- 1- 11 011- 46500000

000038- 76- 2- 2- 151- 14- 17- 3- 2- 950000

000- 2- 9- 4- 1- 4- 3- 4- 10- 2- 6- 12- 8- 5- 6- 2- 3 0000

00074- 2- 4- 4 3- 4- 2- 51- 3303- 2- 3- 3- 7 - 1000

006- 8- 104- 3 10321- 3- 384- 5843- 2- 500

00- 8- 2- 3022025- 60- 50- 6121- 4- 4 - 3100

00- 1- 4- 4- 5- 70- 2- 1- 43- 2- 1162- 6- 4404- 100

05- 4- 45- 3- 401- 48360- 224- 1103- 60- 40

0830550241 331 03931 24675- 1 5600

017- 2- 4340- 1 1408324585444- 7200

05- 2- 51 86352- 1- 351 10- 34245204630

0- 5- 7- 4- 154- 1 872241- 24047331320

0- 424- 553533583581 61 03721 5 - 13- 40

0- 217- 71- 600341 11571 3- 3585- 2 0- 1- 40

0- 1- 3- 315- 24573- 1 214231 154410- 90

071- 890376251 2- 434668560- 13- 30

0- 8- 6- 6- 120- 2 - 4413 2- 32865- 121- 1- 3- 40

032- 351 3147- 251 2 27- 14481 3553100

0- 1- 44431 179841 2 581 04- 181655310

0- 4- 8- 3213355- 13- 1245061712- 350

07- 5- 3- 23941 6945 22266- 60612- 440

01- 2- 423066515 520240521- 2460

00- 3008613360 4- 11204- 3- 2- 4 2100

01- 6- 2- 30576000- 254302- 51- 3 21- 10

06- 2- 3- 354533- 31 0- 3- 2- 201100- 4- 220

03- 4- 405645642 3212- 11311- 2040

040- 114525764 3332- 10121- 2- 270

0- 3- 3157634140 50- 244- 1101- 3- 320

0- 10- 14271 2 1 0064 4244- 14431 1 2130

00- 5- 226645440 73- 2- 112- 21400- 40

03- 5- 261 5389859 65541747- 2 11- 20

01- 4- 1124422- 12 3- 2- 233- 2- 300- 3- 2- 40

0- 32122552263 3050332330- 1- 50

0- 2- 4- 342854432 43231- 130- 1 - 4- 5- 50

0- 10- 1- 701- 1 1- 141 33- 2- 2- 1- 5- 16- 1 - 7- 6- 30

0- 4- 401361- 20- 3- 1- 3- 2- 31- 3- 4- 31- 3 - 5- 9- 50

03245853308- 2 0331- 12011- 30- 10

0- 21- 224- 140151- 14221312- 4 - 4- 3- 10

03- 1397831756 138- 206410- 2- 340

0- 4- 3002214413- 1- 12- 2- 20- 3- 5- 6 - 7- 320

03- 1- 133815542 57070- 32- 4- 6 0110

01- 6- 1- 10655241- 130102- 1- 5- 3 - 2- 2- 10

0- 2- 31- 1651 0 5823 553013- 1- 5- 5 - 2- 220

00304261 0 6634 51334- 41- 3- 2 - 1- 100

01- 6- 205252856 552363- 7- 304010

0- 2- 2- 113275564 343311- 2- 1000- 10

002- 5- 22354786 5537 15- 316- 11- 20

03- 2534899632 1235 331213310

01- 378451 0 4575 44291 061844- 330

004251248471 5052 3- 1101- 1- 300

0- 6- 11- 3431 1 691 15 3064 312291200

0- 13632563456 0302 10- 324- 1- 150

025- 1- 2151461 05 5105- 10- 1724120

02203- 2257630 2003 20- 122- 1240

0- 6- 1 2- 22- 60- 1 721- 1- 34- 10- 3111- 1 - 16- 10

0- 4- 1- 2- 1- 5- 3- 1 - 4- 1- 40- 3- 3- 3- 5- 2- 4- 5- 4- 6 1- 5- 10

0- 7- 6750455014 2312 4- 1- 2- 310- 1- 10

0- 2- 403- 4351- 3- 10- 5- 4- 4- 2 0- 1- 4- 7- 4 - 2- 6- 20

0- 566324616351- 122352- 250- 580

001- 5- 1644010- 5- 4- 1- 125- 310- 4 - 30- 20

0- 2- 1013533750723- 13551- 2 - 5- 440

05674234463531305440- 3 - 5060

06- 351 3331 01 39674- 11 275830- 9 - 2120

0226252465237764675- 4- 4 - 2- 250

0- 11 48730- 2 3156- 1475646- 2- 4 2050

041033- 1181212201511- 1- 3 1050

03- 12858461364221 06630- 1 - 1370

071583453461305569310- 3040

0101 255352500370- 3270- 5- 7 - 4- 1 020

002280- 45652626426621- 4 - 8360

03- 84- 37- 3223327- 510- 11- 21- 6- 1 0 - 150

001 0411- 124456322788557- 2280

0342- 2- 21 31 3 1375581 161 57- 22- 2 041 00

01541- 56- 1 7631 001841 39- 5016060

0- 1- 1563563- 17661 21 3- 11 073- 4- 2 0220

00- 1533- 11 1 184543084811- 1 - 3- 200

0- 3- 1202- 7572436- 110767- 71- 2170

03- 314- 6057346596177413- 2- 1 040

00- 647081 6 731 31 2831 01 01 383- 82- 2- 350

0- 50- 522- 1321 11 066881 01435- 5 - 8- 9- 90

00- 31 0- 15571 51 2222673- 4- 403- 4 1- 400

0074- 1691 21 61 61 41 271 8600- 100- 2 2500

0093- 5- 331 7 1 11 71 21 21 064- 5220- 10- 5- 200

000921 141 2 1 1771 21 378- 6- 1- 8- 4- 132000

000051221 8- 51 31 100- 1 27- 414- 1 100000

000001 4895- 789- 761- 2- 1 1- 23- 900000

0000001 9993- 614- 6- 21- 275000000

00000001 3 - 21 27- 210- 41- 650000000

0000000000- 212780000000000

Quantitative distribution inside the RPV

（inside of the inner wall）

South North small ← Quantity → large

-20 - 1 8 - 1 6 - 1 4 - 1 2 - 1 0 - 8 - 6 - 4 - 2 0 2 4 6 8 1 0 1 2 1 4 1 6 1 8 2 0

 There is more quantity at the RPV bottom (near bottom

head) than usual in some locations.

（Error bar shows only random error.）

Analysis using Muon measurement Simulation（5g/cm ³ )

Simulation（3g/cm ³ )

・ Simulation（1g/cm ³ )

Simulation（0g/cm ³ )

Inside the RPV RPV bottom

（upper side）

RPV bottom

（near bottom head）

Average density of healthy CR guide tube is approx. 0.3g/cm ³

Inside the RPV

Bottom

Quantitative evaluation inside the RPV

quantity [ton]

Error [ton] （Reference）quantity before the accident[ton]

Random

error Systematic error

(Reference)Upper side ^{Approx. 120 ±Approx. 6}

Dozens

Approx.80（structures）

① Core area ^{Approx. 30 ±Approx. 3} Approx.160（fuel assembly）

Approx.15（control rod）

Approx.35（constructions）

② Bottom of the RPV ^{Approx. 90 ±Approx. 5} Approx.35（constructions）

Without effect of water

＜Result＞ (As of September 8, 2017)

＜Evaluation of fuel debris distribution＞

① Quantity of the core area greatly decreased. It is considered that the bulk of fuel and structures moved to lower side. And it is considered there is no massive fuel.

② Quantity of the RPV bottom increased compared to quantity before the accident. There is a possibility that some of fuel debris remain.

＜Evaluation of systematic error＞

Systematic error is evaluated about ±15〜±25 ton considering a resolution limit of the detector to specify the location of targets.

However, there might be several times error more from the factors that simulation could not cover including reinforcing bar inside concrete and constructions installed after the accident.

②Bottom

①Core

（reference）

Upper side

Conclusion

 By measuring muon particles which passed through the reactor building, main structures such as the concrete wall surrounding the PCV, the spent fuel pool and wall of the reactor building

were recognized.

 Evaluation results for the fuel debris distribution inside the RPV by Unit 3 muon measurement are as follows:

 There is no massive fuel debris in the core area.

 There is a possibility that some fuel debris remain at the RPV bottom, though it is uncertain.

 These results and other knowledge obtained from PCV internal

investigation are leveraged towards fuel debris removal in the

future.

Unit 1 Unit ２ Unit ３

• Most of melted fuel fell into the PVC and there is little fuel in the reactor core.

• Part of melted fuel fell into the lower plenum of RPV and the PCV, and part of fuel remain in the reactor core.

• More fuel debris might fall into PCV in Unit 3 than Unit 2.

（Reference）Comparison between Unit 1-3 muon measurement results and estimation of fuel debris distribution

Fuel might be in the core area.

Part of fuel debris at the lower area of RPV

Part of fuel debris

fell into the PCV. Fuel might be in the core area.

Part of fuel debris at the lower are of RPV

Part of fuel debris fell into the PCV.

Most of fuel melted and fell into the PCV.

little fuel in the reactor core

Estimation of fuel debris distribution Estimation of fuel debris distribution Estimation of fuel debris distribution

*”Project of Decommissioning and Contaminated Water Management (Upgrading level of grasping state inside reactor)” (IRID, IAE)

Unit 1 Unit ２ Unit ３（flash report）

・No massive fuel in the core area.

(Lower area of the RPV is not measured.) ・High density materials that is considered fuel debris were found at the lower area of the RPV.

・Part of fuel possibly exists in the reactor core area.

・No massive fuel in the core area.

・There is a possibility that some of fuel debris might remain at the RPV bottom, though it is uncertain.

Results Current estimation of fuel debris d istribution （*）

Results of PCV internal investigation and Muon measurements will be reflected to estimation of fuel debris distribution

Reflect the result to estimation

of fuel debris distribution Reflect the result to estimation

of fuel debris distribution