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Earthquake struck Kashiwazaki-Kariwa Nuclear Power Station (The 2nd news)
At 10:13 a.m. on July 16, 2007, a strong earthquake measuring 6.8 on the Richterscale struck Chuetsu area in Japan, resulting in automatic shut down of unit 2, 3, 4
and 7 at Kashiwazaki-Kariwa NPS as designed, which is located approximately 16
km from the epicenter.Unit 1, 5 and 6 were not in operation for annual outage whenthe earthquake occurred.Although Tokyo Electric Power (TEPCO) is still conducting
investigations, there is no environmental impact.
The maximum acceleration observed at the station was 680 gal.The designed
acceleration at the observation point is 273 gal.Although the earthquake was anexceeding assumption, the reactors in the operating mode were shut down undercontrol, and the units are currently in a stable cold shutdown condition.Since theoccurrence of the earthquake, TEPCO has examined the facilities of all seven
units.The nuclear power plant safety of the station is basically ensuredA detailed
investigation on seismic safety including seismic data analysis will be carriedout.According to TEPCO, seismic wave profile data had disappeared among theseismic data collected from the 63 existing seismographs.(There are total 97
seismographs in the station.)However, the company believes sufficient analyses will
be possible based on all data for the main quake is available for all units.
The Nuclear Safety Commission (NSC) of Japan had a meeting on July 19, andcommissioners reported the result of in-site investigation conducted in themorning.Nuclear and Industrial Safety Agency reported the impact on the station due
to the earthquake in the meeting.TEPCO reported the situation of a fire broken out at
the house transformer of unit 3.
Dr. Suzuki, Chairman of the NSC, stated as follows;
The nuclear power plant safety of the station is basically ensured, the impacts on thestation are not insignificant, including the fire at its transformer facility.Although nosnap decisions should be made in view of further possible fresh and corrected inputs,
the information disclosed so far does not foretell any serious safety impacts on
nuclear reactors concerned.The reactors in the operating mode were shut down undercontrol.The most significant safety measures functioned, as intended in the design, ofprotecting high radiations in the reactors in the multiple-defense and multi-layered
manners.Consequently the nuclear plant safety is maintained and this indicates thebasic appropriateness of seismic regulation concepts including the relevant
regulatory guides. It is not the time to contend the necessity of revising again theseismic regulatory guide.Seismic safety is of highest concern of the nation.The NSC
considers it of particular importance to conduct soonest the necessary safety
checks.Earliest, as practical, evaluations are what the NSC requests to the operator(s)and the regulatory body.
There is new information related to the incidents due to the earthquake as follows;
Resulting from the earthquake, the fire broke out at the house transformer of unit 3,
which was extinguished in about two hours at 0:10 p.m.According to the result of insite investigation conducted by the NSC, the transformer has a fire prevention wall,and it was confirmed that there was no hazard for spreading fire.
Water in the spent fuel pool of unit 6 sloshed around.Some leaked into non radiation
controlled area on the third floor and mezzanine, and was discharged to the sea via adischarge channel.The amount of water discharged to the sea was estimated about
1.2 m3 containing 9 x 104 Bq radioactivity in total.Because the water was diluted to
one-several hundred millionth the legal limit of the activity concentration for
discharge water from the station, which is required by law, it was estimated that there
was no impact on the environment.It is presumed that water spilled over from thespent fuel pool to the reactor building refueling floor (controlled area) subsequently
dripped down to the uncontrolled area via cable and conduit of the refuelingmachine.The discharge had stopped on July 16.

In addition, iodine and particle radioactive materials (chromium 51 and cobalt 60)
were detected at the filter of stack at unit 7 during the weekly survey on July 17.The
amount of radioactivity released from the stack to date is about 4 x 108Bq(equivalent to an exposure of about approximately 2 x 10-7 mSv). Regulatory limitof annual exposure for an ordinary person is 1 mSv, and it was estimated that there
was no impact on the environment.It is presumed that iodine and particle radioactive
materials in the main condensers released via the stack due to the delayedmanipulation for stopping the turbine gland steam exhauster during shut down of theunit.
As of July 19, approximately 70 damages on equipment in the station were identified
and further investigation has been proceeding.
Above information is as of July 19 and will be updated as the further investigation byTEPCO will be carried forward.
Reference:
Nuclear Safety Commission of JapanURL ;http://www.nsc.go.jp/english/english.htm
Tokyo Electric Power Co.URL ; http://www.tepco.co.jp/en/index-e.html

Japan Nuclear Technology InstituteRev. 0
July 20, 2007

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