Reducing Risk at Fukushima Dai-ichi NPS

Toyoshi Fuketa
Nuclear Regulation Authority

Workshop on Decommissioning of Nuclear Power Plants
Hotel Grand Hill Ichigaya Tokyo, JapanApril 8, 2015

1NRAIntroduction
According to the amended Nuclear Regulation Act, theNRA designated the Fukushima Dai-ichi Nuclear Power
Station as “Disaster-experienced Nuclear Power Plant” onNovember 7, 2012, which needs special measures toprevent further disaster and to ensure nuclear security.
The NRA requested TEPCO to prepare an implementation
plan regarding decommissioning processes for Units 1
thru 4, maintaining shut-down status for Units 5 and 6,
monitoring plant status for Units 1 thru 6, physicalprotection, and others.
In order to address risk concerns plainly, the NRA
produced “Measures for Mid-term Risk Reduction” on
February, 2015.

18 February, 2015

Measures for Mid-term Risk Reduction at TEPCO’s Fukushima Daiichi NPS (as of February 2015)
Issue

waste
d Contaminated water

2015

Removing highradioactive
contaminated waterfrom the sea-side pipe
trenches (Units 2-4)
(Mar. 2015; Unit 2)・Completing removalof tanks lacking
concrete foundations
and/or dikes (Apr.
2015)
・Removing
contaminated waterfrom bolt-joint tanks

Preventing the outflow ofcontaminated groundwater into
the sea by completing the seaside underground impermeable
wall including sub-drain control
systems

Earthquake /TsunamiWork environment

Preventing
scattering ofradioactive waste
duringdecommissioning
processes

Managing off-site
effective dose
duringdecommissioning
processes

Removing fuelfrom Spent Fuel
Pools (SFPs)

Site andenvironmental
protection from
Earthquake /TsunamiEnabling asustainable work
environment fordecommissioning

Starting operation ofincineration plants for
miscellaneousradioactive waste e.g.
protective clothing(Oct. 2015)

Accurately controlling
the levels ofgroundwater andstagnant contaminatedwater in R/Bs and T/Bs

Managing theadditional effective
dose to 1mSv/year*
or less (Mar. 2016)

Managing the increase of the total capacity ofwater in tanks by restraining the inflow ofgroundwater into Reactor Buildings(R/Bs) andTurbine Buildings (T/Bs)

2017
Reducing the volume of contaminated waterin tanks by discharging the water afternecessary treatment to the sea inaccordance with the regulatory
requirements, etc.

2019(year)

Managing theadditional effective
dose to 2mSv/year* or
less by continuousradiation monitoring
and by treating highradioactive
contaminated water etc.
(Mar. 2015)

Completing fuelremoval operation
at Unit 4 SFP (Dec.
2014)

Starting operation ofincineration plants forfelled trees
Extending the capacity ofstorage and volume
reduction plants for
rubbles, etc.
Managing secondary wastefrom treatment ofcontaminated water e.g.
sledges in the High Integrity *Estimated value
Container(HIC)s, etc.

Completing constructionof Unit 3 R/B cover andcompleting fuel removalfacility
Completing fuelremoval operation atUnit 3 SFP

Completing constructionof Unit 1 R/B cover andcompleting fuel removal
facilityCompleting fuelremoval operation at
Unit 1 SFP

Implementing the site protection
measures following the established plan

2016

Treating highradioactive
contaminated water intanks (May. 2015)

Spent fuelPreventing the outflow of stagnant
contaminated water anticipating therecurrence of the 2011 Tsunami

Avoiding leakage of contaminatedwater from tanks etc.

Effective dose at
the site boundary(estimated value)

Scientifically providing the greater
earthquake/tsunami model, and establishing
the basic protection plan that corresponds
to this model

Objective

Radioactive
waste

Building thelarge resting
facility(Mar. 2015)

Understanding
the internalsituation of thedamagedfacilities

Building thefood-service
center(Mar. 2015)

Managing a work
environment
not requiring fullface mask
respirators
excluding thevicinity of R/Bs
etc. (May. 2015)

Completing on-site
decontamination excluding thevicinity of R/Bs etc. (Mar. 2016)[Note]
Completed measures:
Measures in progressor in preparation:
Measures (Timing TBD):

Examining theinside of the
facilities

Examining theprocess ofaccumulation ofcontaminatedwater in R/Bs, etc.

Characterizing nuclides
in water passingthrough the reactors

Facilitating administration of
the workers by completingthe new main office building(Aug. 2016)
Analyzing thecontamination of theinside of R/Bs, etc.

Directly observing
inside of PrimaryContainment
Vessels(PCVs) andReactor Pressure
Vessels(RPVs)

3
NRA

This presentation covers;
Most significant concerns are;Water removal and stabilization in undergroundtrenches connected to the reactor turbine buildingson the seaward side,
Fuel removal from spent fuel pool of Units 1 thru 4,
Water decontamination and management ofprocessed water, andWater levels management in order to reduce inflow
of ground water into reactor and turbine buildings.
Another several issues regarding the decommissioning.

4NRA

1 Underground Trenches
The NRA considers that a risk of water leakage fromunderground trenches connected to the reactor turbine
buildings on the seaward side is most significant.
e.g., ~1015 Bq of Cs-137 in Unit 2 trenches(estimated in July 2013)

Trench for
SW pipes

T/B
Reactor No.4

Trench for
SW pipes

T/B
Reactor No.2

VST/B
Reactor No.3

1/4

5NRA

①立坑からの閉塞材料投入により，トンネルの閉塞開始。
②トンネルを閉塞後に、③立坑の閉塞を実施④立坑Ｂ下部の砕石層を閉塞し、閉塞完了

Ｎ
立坑Ｂ

立坑Ｂ

２号機海水配管トレンチ

Ｃネル
トン

トンネルＡ

※ポンプで汚染水が抜き取りきれず、残水する可能性が想定され、各立坑に抜き取り口が必要

立坑Ｄ
立坑Ａ
開削ダクト

２号機タービン建屋

汚染水抜
き取り口

【平面図】
【鳥瞰図（概略）】

閉塞材料
充填口
砕石・水中コンクリート等で上部を閉塞

閉塞材料
充填口

閉塞材料
汚染水抜
充填口
き取り口

閉塞材料
充填口汚染水抜
立坑B

立坑A

立坑Ｃ

トンネルＢ

立坑D
開削ダクト

立坑C

き取り口

汚染水抜
き取り口
開削ダクト

③ P

③③
②66m
トンネルA
1/30
0①

④77m
6１m

56m

トンネルB

PP
1/30
0①P

トンネルC

1/300※施工ステップで色分けをしているが同一材料により打設

2/4

6NRA

Material-3

Vertical Shaft to beclosed out

Material-3
Material-2

Material-1
Material-3

VS to beclosed out

Material-2
Material-1

Closed out tunnel

Material-3
Material-2

Vertical crosssection of vertical
shaft

Closed out tunnel
Image of the work closing out
with each material

3/4

7

Work Progress

NRA

Trench for
SW pipes

T/B
Reactor No.4

Trench for
SW pipes

T/B
Reactor No.2

VST/B
Reactor No.3

as of Feb 6th
Unit 2

Unit 3

Unit 4

Residual water~1,890 m3~3,480 m3~440 m3

Cemented~2,610 m3~2,320 m3~460 m3
4/4

82 Spent Fuel Pool

NRAFuel removal from spent fuel pool of Unit 4 was completed
on December, 2014. This corresponds to ~49% reduction ofspent fuel assemblies in spent fuel pools of Units 1 thru 4.

Unit

1234Capacity
SFA
FFA
Total

900
292
100
392

1240
587
28
615

1220
514
52
566

1590
1331
202
1533

1/5

Fuel-handing machine and crane for Unit 3 SFP
NRACover for fuelremoval work

Fuel-handlingmachine

9Tensile truss Trolley

Tensile truss
Auxiliary hoist
Grabbing equipment

Fuel Handling Machine

Conceptual drawing

CraneCrane
Operating Floor

CoverGirderBase of cover forfuel removal work

Frames for supporting
fuel handling facility

Base of cover forfuel removal work

2/5

Fuel-handing machine and crane for Unit 3 SFP

10NRA２１

DomeGirder
４３

Fuel-handling machineＮ

3/5

11NRA

Fuel removal from Unit 3 SFP
To be made with remote-control fuel-handing machine and craneSetting up rail and girder requires manned operation, so precedentarrangements, debris removal, decontamination and additionalshielding, are needed.

SFP

Relatively high dose rate

4/5

12NRAUnit 3 SFP Gate

G2 gateSFPReactor
wellView
G1gate
FHM

View

5/5

13NRA

3 Water decontamination

Contaminated water in R/Bs & T/Bs is treated and injected back to RPVs.
App. 400m3/day of groundwater is intruding into R/Bs & T/Bs and it forces thecapacity of tanks increase.
Reactor cooling injection: App.300m3/day
Equipment forprocessing R/Oconcentrated
waterSr
Removalequipment

1/7

14NRA

Water decontamination process
Contaminated water in reactor/turbine buildings
Cs137: ~107 Bq/L, Sr90:~107 Bq/L
dated SARRY/Kurion

current SARRY/Kurion

Salt treatment/condensation with RO membrane

Intermediate A (Cs reduced)
Cs137: ~104 Bq/L, Sr90:~108 Bq/L
Sr reduction
Multi-nuclides removalwith ALPS

Intermediate B (Cs & Sr reduced)
Cs137: ~103 Bq/L, Sr90:~106or7 Bq/L

Treated water
Cs137: ND, Sr90: ND, but Tritium: ~106 Bq/L

2/7

15NRA

Water decontamination system
ALPS

250m3/d x 3 units

Improved ALPS

250m3/d x 3 units

High-performance ALPS

500m3/d x 1 unit

R/O water treatment

500m3/dMobile Sr removal*

300m3/d x 2 units
480m3/d x 4 units

SARRY

600m3/d x 2 units

Kurion300m3/d x 3 units*Circulation processing

3/7

16Water storage

NRA1Mm3

Total tank capacity

Treated water +Int. A
0Spring 2014

4/7

Summer 2015

17NRA

5/7

18March 12, 2015

NRA

G4

G7

J1

Int. A
J6

H1Int. B
Treated

K1

K2

6/7

NRA

Achieving less than 1 mSv/y at border

19

G4

G7C

J1

Int. A
Int. B
H1

Treated

K1

K2

7/7

20NRA4 Reduction of groundwater inflow
The water level in reactor/turbine buildings must be always
lower than ambient groundwater level.
The difference between the two levels, however, should becontrolled at adequately small in order to reduce the inflow.

1/4

21NRA

Sub-drain and sea-side impermeable wall
Sub-drain

Groundwater bypass

Groundwaterdrain
Sea-sideimpermeable
wall

Groundwater level

Impermeable layer

in 314 days

Bq/dayCs-1373.8x1011

1.2x109

Sr-90

8.5x1011

2.7x109

Estimation for a period from 4/16/2014 to 2/23/2015

2/4

22

Land-side impermeable walls

NRA
Frozen wall

Frozen wall

Water supply

Water supply

Sub-drain

Sub-drain
Sea-sideimpermeable
wallImpermeable layer

Water
Transferpump

Groundwater
drain

3/4

23NRA

4/4

24
NRA+

Other issues

Protection against earthquake and tsunami
Drainage ditches
Work environment
Facility investigation

25
NRA

Earthquake and tsunami~270gal and 3.122m; DB at initially licensed in 1966
600gal and OP+14.13m; aseismic design back-checkin 2009 and re-evaluation in 2012 for outer-riseearthquake
900gal and OP+26.3m; under evaluation

NRA

26

Water in drainage ditches

Ditch “K”

in 314 days

Bq/dayCs-1371.5x1011

4.8x1081.5x1010

4.7x107

Estimation for a period
from 4/16/2014 to 2/23/2015 Sr-90

Work environment
NRAe.g., reduction of work area with full-face mask

27

Action to be made toward designating area colored with pink as an area in which wearing full-face mask is notnecessary(1) Series of dust monitor equipment will be installed at appropriate spots and data from these monitors will betransmitted to the anti-earthquake building so as to monitor dust level in the building. (February or March 2015)(2) Get permission from the government after confirming that dust level is low enough. (March or April 2015)(3) Certain area is controlled as an area in which wearing full-face mask is not necessary. (In operation in May 2015)

In tank area, risk of taking
concentrated salt water (highlycontaminated with Sr) should beconsidered in addition to the risk
regarding dust level.

Full-face mask unnecessary area
Future operation of Full-face mask
unnecessary area is considered●Equipment for monitoring dust level in an area in which wearing fullface mask is not necessary (5 spots)●Equipment for monitoring dust level at vicinity of reactors (3 spots)○Equipment to be installed additionally by Mach 2015 (2 spots)

Total of 10 areas are tobe moniteredExamining Inside of the Facilities

28NRA• Understanding the inside of R/Bs, Primary Containment Vessels (PCVs) and Reactor
Pressure Vessels (RPVs)• Investigation of the flow paths in R/Bs, etc.
• Analysis of water passing through the reactors• Analysis of the contamination of the inside of R/Bs, etc.
• Direct observation of the inside of PCVs and RPVs

Unit 1

Investigation ofwater leak locationfrom PCV done byTEPCO

SurfaceboatSource: TEPCO
handouts_131113_11-e.pdf

Leak flow

29
NRA

NRA’s challenge

In order to keep reducing the risk existing at the Fukushima
Dai-ichi, the NRA should regulate and promote thedecommissioning processes at the same time.
The important challenge is to maintain harmonization
between the implementation and acceleration of thedecommissioning and the protection of people and theenvironment during the processes.