Niigata-Chuetsu-Oki Earthquake in Japan
Kashiwazaki-Kariwa Nuclear Power Station

The Earthquake at the Kashiwazaki-Kariwa Nuclear Power Station*Kashiwazaki-Kariwa NPS (K-K NPS) is located north side from Tokyo, about 200km.
*K-K NPS of Tokyo Electric Power Co., INC (TEPCO) is the largest NPS in the world,which has 7 Units of BWR bigger than 1,000 MWe.

Units Status at the time of the earthquake
Operating: Unit 3, 4, 7
Starting Up: Unit 2
Outage: Unit 1, 5, 6
Acceleration recorded by seismometers exceeded designed value.

Unit No.
Electric Power (MWe)Commercial Operation
Reactor Type

11,100
1985

2
1,100
1990

Mk. II3
4
1,100 1,1001993
1994
BWR
Mk. II Mod.

51,100
1990

6
1,356
1996

71,356
1997

A-BWRTotal
8,212-

K-K NPS

Acceleration of Earthquake (Unit: gal
1G=980gal)
Records of the reactor building lowest floor
Design values for the same location
North-south
East-west
Up-down
North-south
East-west
Up-down

Unit
No.
1311
680
408
2304
606
282
3308
384
311
4310
492
337
5277
442
205
6271
322
488
7267
356355* The up-down values in brackets are used in static design only.

274
167
192
193
249
263
263

273
167
193
194
254
263
263

(235)*(235)*(235)*(235)*(235)*(235)*(235)*

Safety of K-K NPS★
●PacificOceanTokyo

Overview of the Kashiwazaki-Kariwa NPS

K-K NPS is about 200 Km north of Tokyo(1)Actions during and after the earthquake
a. Operating/Starting up Units were Scrammed automatically by earthquake signal
according to design plan (scram value=120 gal).
b. Emergency DG had not started, since offsite power was maintained.
c. All units were cooled down in a safe manner and maintaining stable condition.
d. No radioactive abnormal indication was revealed (except for the negligible release ofradioactivity)

Photo: Courtesy of The Tokyo Electric Power Company, Inc

Niigata-Chuetsu-Oki Earthquake*Data:
10:13 am on July 16*Magnitude:
Richter Scale 6.8*Epicenter:
16 Km north of K-K NPS*Source Depth: 17Km

Offsite Power had not failed

Fuels were cooled
SFP Water
was released (Unit 6)

Picture: Courtesy of The Tokyo
Electric Power Company, IncSome Old Wooden Houses were destroyed

No damageon SSCs

House Transformer
was fired (Unit 3)Fire Protection Water
flowed into the bldg.
(Unit 1)
Radioactive Gas
was released (Unit 7)
Suppression Chamber

BWR System

Railway was bent

Few Concrete Building were damaged

CR inserted(2)Major Incidents
Damage was not observed on safety-related structures, systems, and components(SSCs). Some incidents of non-safety grade SSCs were as follows.
a. The House Transformer of Unit3 was on fire, and the fire was extinguished 2 hours later.
b. Negligible radioactive materials were released from Unit 6 and 7, but now are stopped.
c. Internal flooding of Unit 1 building by water for fire protection was occurred.
d. Bolts for the foundation of some big water tanks and transformers were cut off.

Niigata-Chuetsu-Oki Earthquake in Japan- Incidents at Kashiwazaki-Kariwa Nuclear Power Station(I) A Fire on the House Transformer of Unit 3

Internal Flooding of Unit 1*The House-Transformer (H-Tr.) of Unit 3 which supplies only non-safety-related SSCs
with electricity was on fire after the earthquake.
*TEPCO's fire brigade hurried to the scene of the fire, but could not extinguish the fire
because of the damage of fire protection piping.
*The fire was extinguished by the municipality fire brigade with fire engines 2 hours
after it began.
*No damage appears in the Main-Transformer and the turbine building around the H-Tr.
by fire walls and interspaces.

*The fire protection (FP) piping near the building of Unit 1 was damaged, and the FP
water flowed into the Reactor Combination Building of Unit 1.
*Approximately 2,000m3 FP water accumulated at the bottom floor.
*Many of equipment for the waste disposal are installed on the bottom floor of theReactor Combination Building. However, it seemed that the flood didn't submerge thesafety-related equipments such as Emergency Core Cooling System (ECCS) of theReactor Building.

Fire Wall
Secondary Duct

Fire Wall
Unit 3 Bldg.

FP piping

H-Tr. of Unit 3Rupturedamaged fire protection piping

Overview of the fired transformer

The ground including the baseof Second Duct sank down, but
the bases of transformer andUnit 3 Bldg. on the bedrock
kept the same level.

FP water flowed into
the building throughthe damaged cable
penetration
Water puddle depth：App. 48cm
Amount:App. 2,000m3
After repair
Photo: Courtesy of the Tokyo Electric Power
Company, Inc

Slippage andoil leak

Guessed Structure of Transformer

Reactor Combination
Building

Reactor Building*Secondary Duct sankdown by 30cm and thebushings were broken.
*Arc strike assumed toinitiate the fire of leaked
oil from transformer.
Mud accumulated on the floor under the inflow hole

Fine sand covered over the floor after FP water flowed

Niigata-Chuetsu-Oki Earthquake in Japan- Incidents at Kashiwazaki-Kariwa Nuclear Power Station (II) Radioactive Material Release Water of Spent Fuel Pool released from Unit 6

Radioactive Gas in Low Pressure Turbine released from Unit 7*Water of Spent Fuel Pool sloshed by earthquake, and splashed on the operating floor.
*Splashed water was released through the cable penetration of the Refueling Platform
to the Sea.
*Exposure dose would be 2 x 10-9 mSv and substantially lower than 1 mSv, thelegally-defined limit of radiation dose to the public per annum.

*Turbine Gland Steam (TGS) which seals Turbine System is specially supplied from theAuxiliary Boiler (Aux. Boiler).
*Aux. Boiler stopped to supply TGS for the turbine system due to the earthquake, andradioactive gas in the turbine and condenser released into the atmosphere through the TGS
exhausted pipe.
*Exposure dose would be 2 x 10-7 mSv and substantially lower than 1 mSv, thelegally-defined limit of radiation dose to the public per annum.

Splashed waterby quake
TurbinePuddleLeakRoute

Cable Penetration(Leak Path)

Condenser*Earthquake splashed SFP water on the operation floor of thereactor combination building (radiological controlled area). Thewater then flowed into the cable junction box of the Refueling
Platform near SFP, and leaked into the path of the cable
penetration.
*The conduit tube under the operating floor, leads tonon-controlled areas of the building. Leaked water of theconduit tube dripped on the lower floor of the non-controlledarea.
*The puddles on the floor flowed into the non-radioactive
wastewater tank along the drain, and pumped out into the sea.

GlandPacking

GlandPacking

Fig 1.In Normal Operation

Fig 2. In This Incident

Turbine Isolation System*The cause of the leakage is believed delay of the stop of the TGS exhauster after automatic
reactor shutdown.
*The TGS exhauster normally exhausts supplied TGS (blue line of Fig 1). But in thisincident, TGS exhauster was continuously in operation, though TGS was stopped to supply.
*It is suspected that the iodine and radioactive gas in the turbine, were blown out by theTGS exhauster (red line of Fig 2), and released into the atmosphere through the stack.

Summary of the radioactive materials Release
Items
Release Cause
Cable Junction Box

AmountExposure dose
Current
Condition
Overview of Operating Floor
Photos and Pictures: Courtesy of the Tokyo Electric Power Company Inc.

Cable Penetration

Unit 6
Unit 7Degradation of cable penetration Delay of the stop of the TGS exhauster
which was the path of release
after automatic reactor shutdown.
Approx. 9E4 Bq (in the sea)
Approx. 4E8 Bq (in the atmosphere)
Approx. 2E-9 mSv
Approx. 2E-7 mSv
Substantially lower than 1 mSv, the legally-defined limit of radiation dose to
the public per annum*Splashedwateron
the *TGS exhauster of unit 7 was stopped
operation floor was wiped up.
and the release of radioactive*The release of radioactive
materials had stopped.
materials has stopped*The radiation monitors of all Units
don’t indicate unusual measurements