measures against earthquakes and tsunamis in view … documents/action 01... · i. impact of the...

Yoshinori MoriyamaDeputy Director-General for Nuclear Accident Measur es

Nuclear and Industrial Safety Agency (NISA)

Measures against Earthquakes and Tsunamis in View of the Accident at

Fukushima Daiichi Nuclear Power Station

Nuclear and Industrial Safety Agency

Ministry of Economy, Trade and

Industry

IEM 3: International Expert’s Meeting (Earthquakes /

Tsunamis)4-7 September, 2012

Vienna

I. Impact of the Earthquake / Tsunami on Fukushima D aiichi Nuclear Power Station

II. Situation of Seismic Safety Assessment Activity in Japan before the Great East Japan Earthquake

III. Re-investigation of Earthquakes / Tsunamis Asse ssment based on Findings and Lessons from the Earthquake / Tsunami

IV. Approaches and Implementation of Safety Counterm easures related to Earthquakes/ Tsunamis

V. Conclusion

Contents

1

I. Impact of the Earthquake / Tsunami on Fukushima Daiichi Nuclear Power Station

2

3

I.(1) Outline of the Accident at Fukushima Daiichi Nuclear Power Station

Fukushima Dai-ichi NPS

Occurrence: 14:46 March 11, 2011

Mw (moment magnitude): 9.0

Epicenter: approximately 130km off the coast of Sanriku (at 38.10 degrees north latitude, 142.86 degrees east longitude and 23.7km deep)

Table. Generation Facilities at Fukushima Dai-ichi NPS

Unit 1

Unit 2

Unit 3

Unit 4

Unit 5

Unit 6

Electric output (MWe) 460 784 784 784 784 1100

Commercial operation 1971/3

1974/7

1976/3

1978/10

1978/4

1979/10

Reactor model BWR3

BWR4 BWR5

PCV model Mark-1 Mark-2

Number of fuel assemblies in the core

400 548 548 548 548 764

Max. Acceleration Values Observed in Reactor Buildings of each Unit

Loc. of seismometer(bottom floor of

reactor bld.)

Record Max. response acceleration to the design basis ground

motion Ss (Gal)Max. acceleration (Gal)

NS EW UD NS EW UD

FukushimaDaiichi

Unit 1 460*１ 447*１ 258*１ 487 489 412Unit 2 348*１ 550*１ 302*１ 441 438 420Unit 3 322*１ 507*１ 231*１ 449 441 429Unit 4 281*１ 319*１ 200*１ 447 445 422Unit 5 311*１ 548*１ 256*１ 452 452 427Unit 6 298*１ 444*１ 244 445 448 415

4

*1：Each recording was interrupted at around 130-150(s) from recording start time*2：1Gal=0.01m/s2 , 981Gal=1G


0.02 0.05 0.1 0.2 0.5 1 2 5

0

1000

2000

3000

周期(秒)

加

速

度

(cm/s )

2

(h=0.05)

Unit2 EWResponse Spectrum

LegendObservedDBGM Ss-1DBGM Ss-2DBGM Ss-3

Acc

eler

atio

n (g

al)

Period (s)

Text added by NISA to published materials from Niigata Prefectural Technology Committee and Google

Flooding

Counterflow

5

Assumed Height and Actual Height of Tsunami in Fukushima Dai-ichi NPS

Fukushima Daiichi


修正中

〔Fukushima Daiichi NPS〕

10m

Destructive flood

Sea water pumps were flooded. Damage to the buildings was slight.

D/G in the basement submerged.

The inundation heightapproximately 15m

Onahama Port

5.7m

4m

Progress of the Accident (Outline Common to Units 1-3)

Automatic reactor shutdown due to earthquake, loss of off-site power supply

(Only one of emergency air cooling DGs in Unit 6 maintained its function)

� Emergency diesel generator started up and power supply was secured.

� Reactor was cooled by core cooling system.

Most of electric systems including emergency diesel generators and switchboards were unavailable due to tsunami.

Hydrogen explosions occurred in reactor buildings at Units 1, 3 and 4.

Soaking / depletion of battery, depletion of compressed air, etc.

Shutdown of core cooling system

Fuels were exposed and melt down while cooling was not conducted.

6


(On March 13, Unit 5 received power supply from Unit 6 on emergency basis. )

Station Blackout

7

ReactorPressure VesselControl Rods(Insertionality)

Core support structures

Main Steam System Piping

Reactor ContainmentVessel

RHRSPump

Residual HeatRemoval System Piping

I. (2) Impact of Earthquake on Facility

Estimated that facilities had remained in a state to maintain safety function at and immediately after earthquake.

Assessed by seismic response analysis using observation record.

Conducted field validation for #5, which was not affected by hydrogen explosion or radiation.

“Cooling”� Residual Heat Removal System Pump� Residual Heat Removal System Piping

“Containing”� Reactor Pressure Vessel� Main Steam System Piping� Reactor Containment Vessel

“Stopping”� Control rods

(Insertionality)� Core support structures

Major 7 facilitiesOn-site check ( In PCV unit 5 )

8


Investigate whether temperature and / or pressure in pressure vessel or containment vessel varies in the case of slight leakage caused by damage to piping, etc.

No significant difference in Reactor Pressure and Water Level in case of leak area less than 0.3cm 2

RPV

ＩＣＩＣＩＣＩＣ

SR/VSR/VSR/VSR/V

RPV

ＩＣＩＣＩＣＩＣ

SR/VSR/VSR/VSR/VAssumed Leak Point （（（（））））

Analysis of Leakage from PLR-B line （（（（0.1～～～～0.3cm2）））） Fukushima Daiichi Unit-1

Sensitivity Analysis

Comparison with actualplant behavior

PLR-A PLR-B

Reactor Pressure and Water Level（（（（RELAP5））））

TIME TIME

RP

V P

ress

ure

[MP

a,g]

Leve

l abo

ve T

AF

[m

m]

-6000-6000-6000-6000

-4000-4000-4000-4000

-2000-2000-2000-2000

0000

2000200020002000

4000400040004000

6000600060006000

8000800080008000

3/11 14:453/11 14:453/11 14:453/11 14:45 3/11 15:003/11 15:003/11 15:003/11 15:00 3/11 15:153/11 15:153/11 15:153/11 15:15 3/11 15:303/11 15:303/11 15:303/11 15:30 3/11 15:453/11 15:453/11 15:453/11 15:45 3/11 16:003/11 16:003/11 16:003/11 16:00

Plant data (NR)Plant data (NR)Plant data (NR)Plant data (NR)

Zero LEAK (Analysis)Zero LEAK (Analysis)Zero LEAK (Analysis)Zero LEAK (Analysis)

0.1cm2 (Analysis)0.1cm2 (Analysis)0.1cm2 (Analysis)0.1cm2 (Analysis)


Reactor Water Level

0.00.00.00.0

1.01.01.01.0

2.02.02.02.0

3.03.03.03.0

4.04.04.04.0

5.05.05.05.0

6.06.06.06.0

7.07.07.07.0

8.08.08.08.0

3/11 14:453/11 14:453/11 14:453/11 14:45 3/11 15:003/11 15:003/11 15:003/11 15:00 3/11 15:153/11 15:153/11 15:153/11 15:15 3/11 15:303/11 15:303/11 15:303/11 15:30 3/11 15:453/11 15:453/11 15:453/11 15:45 3/11 16:003/11 16:003/11 16:003/11 16:00

Plant dataPlant dataPlant dataPlant data

Zero LEAK (Analysis)Zero LEAK (Analysis)Zero LEAK (Analysis)Zero LEAK (Analysis)



EarthquakeEarthquakeEarthquakeEarthquake

SCRAMSCRAMSCRAMSCRAM

IC StartIC StartIC StartIC Start

IC manually StopIC manually StopIC manually StopIC manually Stop

IC manually Start/StopIC manually Start/StopIC manually Start/StopIC manually Start/Stop

（3 times）（3 times）（3 times）（3 times）

Recording Stop due to TsunamiRecording Stop due to TsunamiRecording Stop due to TsunamiRecording Stop due to Tsunami

Reactor Pressure

Changes of plant parameters in case of micro leakage (0.1 - 0.3cm2) after earthquake

9

Conclusion of assessment at this moment


- It is estimated that major facilities with functions important for safety remained in a state to maintain required safety functions at and immediately after the earthquake.

- It remains, however, uncertain at this moment whether such damage that caused slight leakage to major facilities with functions important for safety occurred due to impact of this earthquake.

It is necessary to continue investigation on the impact of the earthquake.

II. Situation of Seismic Safety Assessment Activity in Japan before the Great East Japan Earthquake

10

� Consider active fault 50,000 years ago

� Expect “Earthquake occurring directly underneath” with a magnitude of 6.5.

� Conduct survey of active faults by means of literature searching, aerial photo Interpretation, field survey, etc.

� Ground motion assessment by empirical formula based on earthquake scale and distance from epicenter (Response-spectra)

� In addition to attenuation relation, adopt extensively a fault model as ground motion assessment method.

� In addition to conventional investigation, conduct comprehensive active faults investigation using geomorphology.

� Extended to “120,000 -130,000 years ago”

� Establish more severe “Ground motion developed with non-identified seismic source ”.

Require development of design basis ground motion taking latest knowledge into consideration

Former guideline New Regulatory guide by 2006 amendment

II. (1) Revision of Seismic Design Regulatory Guide

Further, concept of “Residual Risk” is introduced.11

Phenomena accompanying earthquake

・ Tsunami, Surrounding slope stability

September 19, 2006Nuclear Safety Commission amended seismic design re view guide

July 16, 2007Chuetsu - Oki Earthquake occurred in Niigata Prefect ure.

II. (2) Outline of Seismic Back Check

12

September 20,2006

NISA required the nuclear operators to re- evaluate seismic design of all existing NPPs according to revised guide. (Back Check)・Geological survey・Re-evaluation of

Design basis ground motion (Ss) →Seismic safety of NPP facilityGround stabilityPhenomena accompanied with earthquake (Tsunami, Slope stability)

Nuclear operators started re-evaluation.

II.(3) Post- Chuetsu - Oki Earthquake Response

Date and time of occurrence: July 16, 2007Around 10:13 a.m.

Epicenter：Offshore Chuetsu, Niigata PrefectureScale of earthquake: moment magnitude 6.6Depth of epicenter：17 kmEpicentral distance : Kashiwazaki-Kariwa NPS –Epicenter approximately 16 km

Outline of Chuetsu - Oki Earthquake

Observed Value

SN Direction EW DirectionUp-and-Down

Direction

#1 Unit 311(274) 680(273) 408(235)

#2 Unit 304(167) 606(167) 282(235)

#3 Unit 308(192) 384(193) 311(235)

#4 Unit 310(193) 492(194) 337(235)

#5 Unit 277(249) 442(254) 205(235)

#6 Unit 271(263) 322(263) 488(235)

#7 Unit 267(263) 356(263) 355(235)

( ) indicates acceleration expected at design (Unit：Gal)

Maximum acceleration observed on the reactor building base mat at Kashiwazaki-Kariwa NPS

10km

30km

Epicenter

KK site

10km

30km

Epicenter

Power Station

0.01 0.02 0.05 0.1 0.2 0.5 1 2 5 10

0.5

1

2

5

10

20

50

100

200

500

1000

5

0

1

0

0

2

0

0

5

0

0

1

0

0

0

2

0

0

0

(c

m

/

s )

2

0

.0

1

0

.1

1

1

0

(c

m

)

周期(秒)

(h=0.05)

Velocity（cm

/s）

Response spectrum derived

from general attenuation

equation

６ times

Average of observed record

Period (Sec)

Comparison between response spectrum derived

from general attenuation equation from the scale

of Chuetsu-oki Earthquake ( Black line) and that

observed ( Blue line)

Unit 1 (EW)Unit 2 (EW)Unit 3 (EW)Unit 4 (EW)

“1 Unit Observed record ：680 GalExpected response at design：273 Gal Approx. 2.5 times

(Observed example)Observed response significantly beyond expectation at design

13

II. (2) Outline of Seismic Back Check

14

September 19, 2006Nuclear Safety Commission amended seismic design review guide

September 20, 2006NISA directed operators to conduct safety assessment of existing nuclear facilities

March 2008Operators submitted interim reports of back check, etc.

July 16, 2007 Chuetsu - Oki Earthquake occurred in Niigata Prefect ure.

NISA compiled knowledge and findings from Chuetsu-oki Earthquake and directed the nuclear operators to follow ( December 2007).

March 11, 2011The Great East Japan Earthquake occurred .

III. Re-investigation of Earthquakes / Tsunamis bas ed on Findings and Lessons from the Earthquake / Tsunami

15

16

III. (1) Characteristics of the Earthquake / Tsunami

It is estimated that the epicenter of the earthquake was in the area offshore of Miyagi Prefecture, the depth of the epicenter was 24 km, the earthquake scale was a moment magnitude of 9.0, the source area was 400 km or more and the width of the fault was 200 km.

It is estimated that plate rupture commenced from the epicenter in the area offshore of Miyagi Prefecture and propagated to multiple epicenter areas, linking each other .

At this moment, the following appears to represent the characteristics of the earthquake / tsunami:

( JMA 5th report with modification by JNES)

M9.0

15:08,Mar. 111km, M7.5

15:25,Mar. 1134km, M7.4

15:15,Mar. 1128km, M7.3

14:46,Mar. 1124km, M9.0

Sou

rce

area

Distribution of aftershocks occurring in about 8 hours after the main shock

17

III. (1) Characteristics of the Earthquake / Tsunami (Cont.)

At this moment, the following appears to represent the characteristics of the earthquake / tsunami: (Cont.)

A wide-area earthquake occurred triggered by a rupture in an area offshore of Miyagi Prefecture because a boundary at a shallow plate along the Japan trench had been fixed and accumulated a long-year deformation, despite the traditional idea that no significant deformation should exist there due to gradual slippage.

Although this was an earthquake of super-large scale with a moment magnitude of 9 from the viewpoint of long-period seismic motion, it had the same characteristics as an earthquake of a moment magnitude class of 8 from the viewpoint of short-period seismic motion.

It is highly possible that the factor which affected the tsunami water level was a combined effect of large slippage (55 m – less than 70 m) in a shallow area along the Japan trench and tsunami water level caused by propagation with time delay during destruction linkage of multiple source areas.

Conduct re-assessment of earthquake / tsunami

18

III. (2) Revision of Regulatory Guide by Nuclear Safety Commission

Contents to be added regarding safety assessment ag ainst Tsunamis

� The design standard tsunami shall be formed considering tsunami of the maximum scale based on the generation mechanism of tsunami and examination of the effects of propagation of tsunami, and then, it should be assumed to have significant impact to facilities.

� Basic concept should be to prevent tsunami from flooding into the site, etc. (so-called “Dry Site ”). In this case, flooding from intake openings, discharge, etc. where preventing from seawater inundation is difficult shall be limited to the extent that safety function of facilities shall not be affected.

Contents to be added regarding seismic motion asses sment

� Consideration of uncertainty (dispersion) such as an source area and/or scale of an earthquake between plates and an earthquake in an ocean plate.

� Safety of facilities against ground structure deformation and fault displacement caused by an earthquake shall be validated.

19

III. (3) Initiative of NISA

(3)-1 Consideration of Guidelines for Safety against Tsunamis

Investigate more specific guideline on assessment of tsunami height, etc.

� Estimate tsunami height, considering;・Appropriate occurrence frequency ・Overlapping of waves with different frequency ・Tsunami sediments

� Consider ・Destructive wave force, water immersion height and water

immersion range, etc. for design of tide embankment, watertight doors, etc.

� From the viewpoint of defense-in-depth, recognizing the existence of risk due to tsunami hitting beyond the design base of facilities, countermeasures should be taken to prevent serious damage to core and fuel in fuel pool.

Tom

ari P

S

20

III. (3) Initiative of NISA

(3)-2 Investigation on Linkage of Active Faults

Detailed investigation was conducted on situation of tectonics, stress, etc. regarding faults of which possibility of linkage had been denied.

Tomari Power Station ：：：：

Assume linkage with an active fault in sea area in front of site (approximately 160 km).

Kashiwazaki-Kariwa NPS ：：：：

Assume linkage with Nagaoka Plains West Edge Fault Belt (Approximately 130 km).

91km

41km

132km

In addition, uncertainty ( stress drop 1.5 times etc.) to be assumed.

Kashiwazaki-Kariwa Nuclear Power Station

Kakuda Yahiko Fault

Kehinomiya Fault

Katagai Fault

Tookamachi Fault Belt western part

21

III. (3) Initiative of NISA(3) -3 Consideration of Uncertainty in Seismic Motion Assessment

Sufficient geographic, geological, geophysical investigation to establish basic source model.

Uncertainties still remain.

3 categories of uncertainties

- Epistemological uncertainty due to lack of data or knowledge.- Aleatory uncertainty due to natural phenomenon.- Uncertainty associated with modeling.

It is necessary to fully investigate what type of uncertainty exists regarding each parameter to establish a source model such as fault length, fault dip and stress drop.

Reflecting experts’ opinions.

IV. Approaches and Implementation of Safety Countermeasures related to Earthquakes / Tsunamis

22

Immediate safety measuresStress testInvestigation of countermeasures against earthquakes / tsunami based on this accident.Countermeasures against severe accidents (external events)Back-fitting system

23

IV. (1) Outline of Immediate Safety Measures

Goals (Desired Level/Extent)

Examples of Specific Measures (Short Term Measures)

Preventing fuel damage and spent fuel damage even if AC power supplies, seawater cooling functions and spent-fuel storage pool cooling functions are all lost.

Securing Equipment

� Deploying power generator vehicles� Deploying fire engines� Deploying fire hoses

Preparing procedural manuals for emergency responses utilizing the above-mentioned equipment

Implementing training for emergency responses based on the procedural manuals

Primary assessmentEvaluate safety margins of safety systems, structures and components to endure the events beyond design basis, for nuclear power plants under periodic inspection and ready for start-up.

Secondary assessmentConduct comprehensive safety assessment to identify potential weak points for all nuclear power plants, as done in European Stress Test.

24

IV. (2) Stress Test in Japan

In order to improve the safety of nuclear power plants and to secure the assurance and trust of the general public and local residents in particular, NISA implements safety assessments in reference to the stress tests implemented in European countries.

Objectives

Summary

25

IV. (3) Consideration of Countermeasures against Earthquakes / Tsunamis based on This Accident

Examples of countermeasures against Earthquakes / Tsunamis to be taken in the future in line with occurrence and sequence of the accident.

Countermeasures concerning offsite power

� From the viewpoint to lower risk of severe accidents;・ Enhance seismic and against-tsunami reliability of offsite power systems

and substation facilitiesOuter power grid : tower, foundationOffsite power station: switch gear, transformer, their baseSwitchyard: switch gear, transformer, their base, tie-line between units

Power facilities and cooling facilities inside pow er station

� For common cause failure;Dispersed facility arrangement ;

Different location (elevation)In different building

� For resistance against flooding; Water tightness of buildings and electric power panelsWater resistant power line

� For emergency cooling;Portable alternative residual heat removal system which is not affected by earthquakes or tsunamis.

26

Natural hazard Aircraft crash Terrorism

IV. (4) Countermeasures against Severe Accidents (External Hazards)

Basic idea of response to external hazards

Intensity

Early detectionShutdown・power down

Durability (actual)

Tolerance

Specific safety equipment

•Seismic isolation,•Dispersion•Watertight structure,•Diversification (Water-cooled + Air cooled)

•Recovery•Alternative equipments (mobile)

Maintenance of safety function

Margin

(1)

(2)

(3)

(4)

All SSCswith safety

function

Frequency of accidents

•Robustness•Dispersion

(Not-considered)

(* unit: reactor･year)

Detection

Delay

Management

Detection

Protection, Isolation

Security order

Intentional

(Commonalities?)

(to external events)

Isolation, Dispersion

(from external events)

Safety function

Recovery, Alternatives

（≦10－７

）* （＞10－７

）*

SpecialSafety Facility(Temporaryname)

27

IV. (5) Back-Fit System

There is now no legal system in Japan that requires back-fit for items related to basic designs such as design ground motion.

Back fit system is to be introduced in line with the legal system revisions based on the Fukushima Daiichi nuclear accident；

・Requiring as legal obligation・Implementing by setting deadline

Important to promptly apply new scientific knowledge to safety measures.

V. Conclusion

28

A lot of factors that affected Fukushima Daiichi nuclear power station due to the earthquake and tsunami have been identified.

However, it is not yet sufficient because of the difficulties in accessing the plant site, and continuous examination should be pursued.

Effort will be made;

- To accumulate scientific knowledge of earthquakes and tsunamis

- To incorporate this knowledge into the safety measures for nuclear power stations.

- To share results investigated in Japan to the international community through IAEA ISSC program, etc.

- To contribute to incorporating this knowledge to IAEA safety guides, etc.

V. Conclusion (Cont.)

29

Recognizing the existence of uncertainties, implementation of safety measures to compensate for uncertainties are required.

It is important to take a comprehensive approach for the improvement of nuclear power safety as a total system.

- Hazard evaluations of earthquakes and tsunamis- Safety measures such as accident management- Emergency preparedness and disaster mitigation- Risk communication with residents, etc.

It is important to address efforts through cooperation among the specialists of different fields and by sharing knowledge and information.We hope discussion in this IEM 3 will improve the knowledge summarized at 1st Kashiwazaki International symposium on Seismic Safety in 2010.

Thank you for your attention

30

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