unit 1 primary containment vessel internal investigation · 2017-07-27 · legend：measurement...

Unit 1 Primary Containment Vessel Internal Investigation〜 Analysis of image data and dose data 〜

Tokyo Electric Power Company Holdings, Inc

July 27, 2017

1

１．Outline of analysis

Measurement points Purpose of measurementD0①〜③ Diffusion of fuel debris from the drain sumpBG Background levels against D0〜D3 measurementD1①②，D2①〜③ Diffusion of fuel debris from pedestal opening

D3 Possibility of fuel debris reaching to the PCV shell

Primary Containment Vessel (PCV)

Cross section of 1st floor PCV

Pedestal opening

CRD railPedestal

BG

D3D2

D1

X-100Bpenetration

We sharpened the images took in March, 2017 and re-analyzed, while examined the possibility of debris diffusion from the pedestal opening using dose data gathered in the investigation.

Positions of image and dose data are as follows:

Drain sump

D0

Extended figure

Extended figure

Legend：measurement date（MM/DD）

Pedestal

Pedestal Drain sump

X-100Bpenetration

Opening

2

Image data of the measurement points were sharpened. Sharpened image of the point D0② shows no extensive deformity and damage of existing structures

including valves, pipes and steels. The checker plate of drain sump was not found due to deposits.original

Valve

SteelPipe elbow

valvevalve

SteelSteel

Near point D0② before disaster

Pipe elbowPipe elbow

Checker plate of drain sump

２．Analysis result of image data（1/2）

sharpened

Position and direction of D0②Drain sump pump

Pedestal side

Pedestal side

Pedestal side

3

Point D0③ Point D1② Point D2③

Obtained

images

Sharpenedim

ages

Fallen object

２．Analysis result of image data（2/2） Image data other than D0② were sharpened too. Fallen object was found at the point D2③. No new information at the points D0 and D1.

4

３．Analysis result of dose data3.1 Estimation of possibility of fuel debris diffusion（1/2）

【Before investigation】 In the case that fuel debris exist at the PCV bottom※ and there are deposits of less than 0.1

m (assuming concrete as deposit in analysis) on the debris, we found it possible to estimate the possibility of fuel debris under deposits.

Distance from floor of the basement [m]

Deposit (approx.0.1m）

Accumulated water

Fuel debrisDo

se r

ate

in w

ater

[Gy/

h]

Dose distribution image

Deposits of approx. 0.1m on the fuel debrisNo fuel debris, only deposit（No dose from deposit)

※ It is assumed that fuel melted the structures in thereactor at the accident and fused with Co-60 in thestructures.

PCV bottom

5

Possibility of fuel debris under deposits was estimated in the following steps:

Main dose source (nuclide) on the deposit surface at point BG where is less affected by fuel debris is determined.

Analysis result at BG and D0③ where are considered to be less affected with fuel debris assuming there is no fuel debris and there is Cs-137 on the deposit surface as main source is to be compared with the measured dose data.

Analysis result at D1 and D2 where there are possibly fuel debris assuming there are main source and fuel debris on the deposit surface is to be compared with the measured dose data, and the possibility of fuel debris diffusion is to be estimated.

Possibility of fuel debris diffusion is estimated.

３．Analysis result of dose data3.1 Estimation of possibility of fuel debris diffusion（2/2）

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【 Point BG 】

Distance from deposit surface [m]

正規

化し

た⽔

中線

量率

[―]

As dose rate measured from the deposit surface※1 is almost equal to Cs-137 decay curve in decay rate by distance, main dose source (nuclide) is considered to be Cs-137.

※1：Impacts of accumulated water and structures are subtracted from the measurement.※2：It is assumed that fuel debris fused with Co-60 in the melted structures in the reactor

at the accident. ※3：Dose rate is normalized by treating dose rate nearest the deposit surface as “1”.

0.1

1

0 0.05 0.1 0.15 0.2

Dose rate measured from deposit surfaceCs-137Approximated curve for measurementFuel debris supposed in analysis※2

△

Norm

aliz

ed※

3 dos

e ra

te in

wat

er[―

]

３．Analysis result of dose data3.2 Analysis of dose distribution – BG: main source on the deposit surface

77

We analyzed BG and D0③ assuming Cs-137 is main source on the deposit surface. It is assumed that there is no fuel debris at BG and D0③, because these points have thin deposits

and enough distance from the pedestal opening. Analysis based on above assumption well-matches with measurement. Therefore, it is considered

that there is no fuel debris under deposits at BG and D0③ or very little even if exist.

堆積物滞留⽔

【 Point BG 】【 Point D0③ 】

0

5

10

15

20

25

0 0.5 1 1.5Do

se ra

te in

wat

er [

Gy/h

]Distance from floor of the basement [m]

測定結果測定結果(参考値)D0③解析値Analysis result

0

5

10

15

20

25

0 0.5 1 1.5

Dose

rate

in w

ater

[Gy

/h]

Distance from floor of the basement [m]

測定結果測定結果(参考値)BG解析値

堆積物 Accumulatedwater

Analysis result

Deposit

PCV bottomPCV bottom

３．Analysis result of dose data3.3 Analysis of dose distribution – Possibility of fuel debris in the deposits（1/2）

Note）◆Measurement：Measured by halting censor◇Measurement（Reference）：Measured by moving censor

(average dose rate)

Measurement (reference)

Measurement MeasurementMeasurement (reference)

Accumulatedwater

Deposit

We have analyzed dose rate in the case of fuel debris exist under deposits of about 0.9m height, in range of deposit height measured at D1 and D2.

Analysis result for point D2③ near pedestal opening is as the figure bellow. Existence of fuel debris cannot be examined in the case of thick deposits due to their shield. The cause examination cannot be done is considered to be that there is no fuel debris, or

that thick deposits and structures have profound shield effect. As the deposit thickness is currently unknown, we cannot determine it.

※ The structures might exist under the deposits.

D2③ Analysis condition( Height of deposits is 0.9m)① Deposit thickness：0.9m② Deposit thickness：0.3m③ Deposit thickness：0.1m

80 0.5 1 1.5

地下階床⾯からの距離 [m]

滞留⽔燃料デブリ

⽔中線量率

[Sv/

h]

0.9m

堆積物※

0

5

10

15

20

25

30

35

40

0

5

10

15

20

25

30

35

40

Deposit※

AccumulatedwaterFuel debris

◆ Measurement◇ Measurement (Reference)

Analysis①(deposits of 0.9m)Analysis②(deposits of 0.3m)Analysis③(deposits of 0.1m)


(average dose rate)

Dose

rate

in w

ater

[Gy/

h]

PCV bottom

３．Analysis result of dose data3.3 Analysis of dose distribution – Possibility of fuel debris in the deposits（2/2）

Distance from basement floor [m]

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４．Conclusion＜Analysis result of image data＞ Analysis of image data at the point D0 near the drain sump shows no extensive

damage and collapse of visible structures (steel, valve) near the drain sump (X-100B side).

＜Analysis result of dose data＞ Main source on the deposit surface is considered to be Cs-137 from analysis. As analysis result at the point BG and D0③ assuming that deposit thickness is

thin and there is Cs-137 on the deposit surface is almost equal to measured dose rate, it is considered that there is no fuel debris or very little even if exist.

Analysis of dose rate at the point D1 and D2 near the pedestal open did not lead any meaningful result about the possibility of fuel debris in the deposits due to high location of deposit surface.

＜Future policy＞ We will discuss the range and the method of the next investigation considering

this analysis result and the characteristics of deposits collected just bellow X-100 penetration.

Reference: Analysis of image dataEstimation of deposit surface height

※1 Height of the deposit surface is calculated from the distance between censor and deposit surfaceobtained by SFM(Structure from Motion) and the dropping length of censor.

・Value in yellow box is estimated height of deposit surface calculated from image analysis.・Value in () is lowest height of hanged censor.・Deposit thickness bellow the deposit surface is unknown.

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D2①

D2②③

D1②

D1①

約1.5m

1.0m(1.0m)

0.9m(0.9m※)

0.9m(0.9m)

0.8m(0.9m)

約3.3m

D0③

0.3m(0.3m)

0.2m(0.3m)

Estimation of deposit surface height from image※1

1st floor grating

Water surface

Approx. 3.3m

PRL pipe

PRL pipe

Pedestal opening

A-A cross section B-B cross section

Basement floor

Approx. 1.5m

※ Height measured by closing censor

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Analysis for various thickness of fuel debris and deposits were carried out.

Reference: Analysis of dose dataDose distribution analysis – possibility of fuel debris in deposit

■Point D1①Analysis condition (Deposit height is 0.8m)① Deposit thickness：0.8m② Deposit thickness：0.3m

■Point D1②Analysis condition (Deposit height is 0.9m）① Deposit thickness：0.9m② Deposit thickness：0.3m

0.8m

堆積物燃料デブリ滞留⽔

0.9m


0

5

10

15

20

25

0 0.5 1 1.5

Dos

e ra

te in

wat

er[G

y/h]


測定結果測定結果(参考値)解析結果①(燃料デブリ無し)解析結果②(燃料デブリ0.5m)

0

5

10

15

20

25

0 0.5 1 1.5

Dos

e ra

te in

wat

er[G

y/h]



注）◆測定結果：センサを⽌めて測定した値◇測定結果（参考値）：センサ吊下げ動作中の線量率の平均値

Analysis ①(0.8m thick deposit)Analysis ②(0.3m thick deposit)



Accumulatedwater

AccumulatedwaterFuel debris

Fuel debrisDeposit Deposit

MeasurementMeasurement (reference)



(average dose rate)

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Analysis for various thickness of fuel debris and deposits were carried out.

■Point D2①Analysis condition (deposit height is 1.0m）① Deposit thickness：1.0m② Deposit thickness：0.3m

■Point D2②Analysis condition (deposit height is 0.9m）① Deposit thickness：0.9m② Deposit thickness：0.3m

1.0m


0.9m


0

5

10

15

20

25

0 0.5 1 1.5

Dos

e ra

te in

wat

er[G

y/h]



0

5

10

15

20

25

0 0.5 1 1.5

Dos

e ra

te in

wat

er[G

y/h]






Reference: Analysis of dose dataDose distribution analysis – possibility of fuel debris in deposit


(average dose rate)

DepositDeposit

Accumulatedwater

AccumulatedwaterFuel debris Fuel debris



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【 Point D2③ 】

正規

化し

た⽔

中線

量率

[―]

0.01

0.1

1

0 0.1 0.2 0.3 0.4

堆積物表⾯からの線量率測定結果Cs-137測定値近似曲線燃料デブリ※1

△

解析で想定した燃料デブリ※1

【 Point D0③ 】

正規

化し

た⽔

中線

量率

[―]

堆積物表⾯からの線量率測定結果Cs-137測定値近似曲線燃料デブリ※2

△

0.01

0.1

1

0 0.1 0.2 0.3 0.4

正規

化し

た⽔

中線

量率

[―]

解析で想定した燃料デブリ※1

Reference: Analysis of dose dataMain source on the deposit surface－D0③,D2③

Distance from deposit surface [m] Distance from deposit surface [m]

Dose rate measurementCs-137Approximated for measurementAssumed fuel debris ※1No

rmal

ized

dos

e ra

te in

wat

er[―

]

Norm

aliz

ed d

ose

rate

in w

ater

[―]

Dose rate measurementCs-137Approximated for measurementAssumed fuel debris ※1

※1 It is assumed that fuel melted the structures in thereactor at the accident and fused with Co-60 in thestructures.

unit 1 primary containment vessel internal investigation · 2017-07-27 · legend：measurement...

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