The Tokyo Electric Power Company, Inc. (TEPCO) has collected and sorted
the seismic observation data recorded during the Niigata-Chuetsu-Oki
Earthquake (magnitude: 6.8, distance from the seismic epicenter: 16km,
distance from seismic center: 23km) that hit the Kashiwazaki-Kariwa NPS
on July 16th, 2007 in order to conduct seismic observation data analyses
and impact evaluation on seismic safety.
We announce the results of the seismic data collected for all seven units
at the Kashiwazaki-Kariwa NPS, including those for units 1, 5 and 6, which
had been previously announced.
At the Kashiwazaki-Kariwa NPS, in addition to the existing seismographs
that were installed in the buildings of units 1, 5, and 6 and on the site
ground (67 in total), new seismographs (30 in total) have been installed
in all seven units and have been functional since April of 2007.
During the course of data collection following the earthquake, we confirmed
that among the seismic data collected from the 63 existing seismographs,
seismic wave profile data had disappeared.
However, we believe sufficient analyses will be possible based on maximum
acceleration data found in the existing seismographs for the main quake;
all data for the main quake is available from the newly installed seismographs
for all units, and subsequent data for the aftershocks are available from
both existing and newly installed seismographs.
The data disappeared due to the fact of that the seismic record for the main
quake had been overwritten by that of the aftershocks. The data was overwritten
because data could not be transmitted to the server located in Tokyo due to
congestion on the communication channel coupled with the consecutive occurrence
of numerous aftershocks.
Similar problems occurred during the Noto Peninsula earthquake that hit the Shika
NPS of Hokuriku Electric, and TEPCO was planning to replace seismographs, including
those of KK (for unit 1 in 2007 and for units 5 and 6 in 2008.)
In light of this incident, we will immediately replace all seismographs in addition
to registering this incident on the NUCIA (NUClear Information Archives) database
for the purpose of informing other utilities.
We will continue collecting seismic data of the aftershocks as well as analyzing
the seismic records, and confirm the seismic safety of facilities that are of
high safety importance.
Appendices
Reference1:The observed seismic acceleraion at the Kashiwazaki-Kariwa Nuclear
Power Plant during the Niigata Earthquake
Reference2:Layout of seismograph installations
Reference3:Image of seismic observation system
|