World Conference on Earthquake Engineering (15WCEE), Lisbon, 24 September 2012
Special Session on “Great East Japan Earthquake 2011”

Accident of Fukushima Daiichi NPP
on March 11, 2011

Tsuyoshi Takada
The University of Tokyo
takada@load.arch.t.u-tokyo.ac.jp

Summary
1. Outline of accident of Fukushima Daiichi NPP
2. Ground motion
3. Great Tsunami
4. Behavior of Plants

5. Conclusion: Lessons learned from Accident

2

Fukushima Daiichi NPPs operated by TEPCO

Unit 6
Unit 5

Unit 1
Unit 2
Unit 3

Unit 4

Source: TEPCO33

NPPs in Eastern Coast of JapanOnagawa(Tohoku)

Fukushima
Daiichi *(TEPCO)

FukushimaDaini(TEPCO)

Tokai-2(JAPCO)* Fukushima Daiichi locates approximately
230 km north of Tokyo4

Nuclear Power Plants in Japan
1F : Fukushima Daiichi
2F : Fukushima Daini

1600

Electrical Output (MWe)1400

BWR : 30 units
PWR : 24 units
CGR, ATR

1200

2F1 2F3
2F2 2F4
1F6

1000
800
600

1F2 1F3 1F4
1F5
1F1

400
20001965

1970

30年
1975
1980

20年
1985
1990

Start of Operation

10年
1995
2000

現在
2005
2010
5

Overview of Mark-I Type BWR (Units 1 to 5)

Reactor Building(R/B)
Spent Fuel Pool (SFP)
Primary Containment
Vessel (PCV)

Reactor Pressure Vessel(RPV)

Dry Well(D/W)

Suppression Chamber (S/C)
66

2. Earthquake Ground Motion

7

Great East Japan
Earthquake

Scope & duration of the ground acceleration@2:46pm local time, March 11th, 2011 hypocenter depth
24Km M9Broad Scope
500km

High Acceleration
more than 500gal
Phase 1

Durationover 2 min.
Phase 2114gal

316galMaximum Ground Acceleration
Distribution Map

Phase 1
prominent

229gal570gal570gal300km region
was shaken by200gal

Bothphases
prominent

411gal

317gal568galPhase 2prominent

296galThere are 2 striking phases (Phase1, Phase2) in theaccelerograms in the new stratum vicinity, whichindicate at least 2 major slips.
In the northern region, the first phase is prominent
whereas, in the southern region, the first phase ishardly visible; only the second phase is visible.
The two phases correspond to the slips in thenorthern and the southern region.
Response to the real-time seismic intensity vary bylocation; however, the slips correspond tomaximum seismic intensity.
There are points where sharp phases are observed
between Phase 1 and Phase 2 (i.e., FK5013, FK5004,MYG017, MYG015)
There are many other visible phases, which
demonstrate the complex seismic source process.

References: Central Disaster Prevention Council reports, etc.

304galPhase 1
hardlyobserved

329gal

212galRecorded Intensity of Ground Motion
and Design Earthquake Ground Motion
Observed Maximum Response
Acceleration *(Gal)Fukushima
Daiichi

Fukushima
Daini

Max Response Acceleration against
Basic Earthquake Ground Motion(Gal), Ss

Horizontal (NS)Horizontal(E-W)

VerticalHorizontal (N-S)

Horizontal(E-W)

Vertical

Unit 1460447258487489

412

Unit 2348

550302

441

438

420

Unit 3

322

507

231

449

441

429

Unit 4

281

319

200

447445422

Unit 5

311

548

256

452

452

427

Unit 6

298

444

244

445

448

415

Unit 1254

230

305

434

434

512

Unit 2243

196232

428

429

504

Unit 3277216208428430504

Unit 4210

205

288415415504* At the lowest basement of reactor building

91011

Aftershocks of March 11 Earthquake

Location of Aftershocks

Occurrence History of Aftershocks (1 year)

123. Tsunami

13Tsunami triggered by the Great East Japan Earthquake
Damage Scenario & Observed Tsunami Run-up Height
A comparison of the Tsunami Run-up Heights of Past 3 Major Earthquakes in the Tohoku Region&3.11 Great East Japan Earthquake
Sendai

Tokai Plant

Matsushima
Bay

Mangoku
Bay

Fukushima Plant

Higashi-dori Plant
RikuzenTakataHachinohe

Onagawa Plant

Why did no one simulate the occurrenceof a Tsunami in the region?

Ibaragi
Pref

Fukushima
Pref

Miyagi
PrefMiyako

Past Tsunamis

Iwate
Pref20m

Matsushima Bay

Mangoku
BayReferences:
Tsunami run-up heights of the scenario 3 major earthquakes: research conducted by the Special Committee on the Countermeasures against Earthquake Disaster in Relation toSubduction Zone Earthquake Around Japan Trench and Chishima Trench.
The Great East Japan Earthquake inundation height & run-up height: research conducted by the Coastal Engineering Committee, Japan Society of Civil Engineers
Other References: Central Disaster Prevention Council reports, etc.

Scenario : 3 Major Earthquakes/Tsunami-Sanriku-oki-Miyagi-ken-oki-Meiji Sanriku Earthquake (1896)
3.11, 2011
● Tohoku-oki inundation height▲ Tohoku-oki run-up height 14Tsunami, March 11, 2011
15:42:40

15:42:46

15:43:26

15:43:36

15:43:54

15:44:18

15:44:44

15:44:58

15:46:10

15.5 m from thesea level

Tsunami height in Fukushima Daiichi
was about 15 m.

Source: TEPCO

15

Comparison of Tsunami Height between Daiichi and Daini
Fukushima Daiichi
Designhighest
tsunami level+5.7m*

Safety measures has
Ocean-side
taken against
5.7m
area
Tsunami height

Inundation height
Turbine+14-15m

Reactor
Building

Building

+4m
Water
Pump

Base level
O.P. 0m+10m

breakwater
Water intake* Site level on Units 5 and 6 is O.P. +13m

* Based on 2002 guidelines for NPPs issued by
the Nuclear Civil Engineering Committee of JSCE

Fukushima Daini
Ocean-sidearea

Main building area

Inundation height apx. O.P. +6.5-7m
Assumed highest
tsunami water level Safety measures has taken against
5.7m Tsunami height
O.P.+5.2m *Site level
Heat exchanger building+4m

Reactor
Building

TurbineBuilding

Water
Pump

Base level
O.P.0m+12m

breakwater
Water intake
O.P.：Onahama bay construction base level16

4. Behavior of Plant17Basic Safety Requirements of NPPPCCVStop

RPVSteamwaterConfine
Reactor pump

Reactor pumpcontrol rods

Suppression chamber

Residual Heat Removal
Pump

Cooldown

Three Fundamental Principles to Prevent Accident

18Differences among Units 1-4 of Fukushima Dai-ichi
 Fukushima Daiichi Units 5 & 6• Elevation of the ground is 13 m. (Units 1 - 4 : 10m)
• One air cooled EDG of Unit 6 which is located on the ground level
was survived.
• Metal Clad Switchgears were not lost.
• Temporary sea water pump installed after the earthquake wasoperable, making use of power from survived EDG.

 Fukushima Daini NPPs
• External power was not lost.
• RHR function of Unit 3 was survived.
• Motors of sea water pumps for Unit 1,2 and 4 were replaced byMarch 14, followed by re-activation of core cooling function.
 Onagawa NPPs
• Elevation of the plants was 14.8m which is higher than Tsunami
height.
 Tokai-2• Although off-site power was lost until May 13, 2 out of 3 EDGs werenot lost thanks to the recently installed barrage to one of 2 seawater
19pump area to protect pumps from tsunami.

5. Conclusion
Lessons learned from Accident

20Lessons learned from Accident
1

Need of appropriate DB scenario for Anti-tsunami design method
based on risk concept

Design basis tsunami height 5.7m against 15m of actual tsunami
height2

Severe Accident Management
Need of robustness and diversity in responding to beyond DBAs suchas station black-out for long-duration, loss of ultimate heat sink-Appropriate design philosophy to sustain safety function against
common cause failures brought by natural hazards-Appropriate AM measures for both prevention and mitigation of SAs

3

Implementation of Seismic PRA and Tsunami PRA
Including their interaction assessment
Response and Preparedness based on residual risk
Effective measure to the unforseen events

4

Total Risk Management (Robustness)
Covering total system behavior and on-site and off-site facilities

21

END
Thank you for your attention.

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