Japan Nuclear Technology Institute

　 Tokyo Electric Power Company has analyzed seismic observation data, obtained during the main shock of the recent earthquake.Upon completing the collection and summarization of all records, we compiled a report (Report 1) outlining the findings of the study thus far and submitted it to the Nuclear and Industrial Safety Agency on July 30, while also publicly releasing the information.This report (Report #5) summarizes and presents the trends identified thus far concerning seismic observation data.The “relative position of the power station against the epicenter of the main shock” and “relative positions of reactor units on the power station compound” are shown in Attachment 1 and Attachment 2 respectively.

Public release of seismic observation data recorded by TEPCO at its nuclear power station

On July 16, when the earthquake struck, the maximum acceleration (observation figures) recorded on the lowest floor (above the mat foundation) of the reactor buildings at Units 1, 5 and 6 as a bulletin report (interim figures), along with the design acceleration response defined for the same locations (design values).

After all units completed gathering and summarizing seismic observation records for the main shock of the earthquake, TEPCO released the observation figures recorded on the lowest floor (above the mat foundation) of the reactor buildings at all units, and design values for the same locations as listed below:

(Unit: Gal)

(Note 1)The figures for Units 1, 5 and 6 are the same as those released on July 16.

(Note 2)The up-down component figures in brackets are used in static design.

Instruction from the Nuclear and Industrial Safety Agency

　 The observation figures on the lowest floor of the reactor buildings at Units 1, 5 and 6 were above the design values based on the standard seismic motion defined.Based on the finding, the Agency instructed TEPCO to report on the following:

Analysis of seismic observation data obtained during the recent earthquake

Confirmation of seismic safety of important plant facilities in terms of safety in respect to the recent earthquake

<Report outlines>

The comparison between the “floor response spectrum based on observation records” observed on the lowest floor of the reactor buildings at Units 1 to 7 and “floor response spectrum calculated based on the Design Basis Earthquake Ground Motion in the seismic response analysis model used in the design stage”, are presented in Attachment 3.
These figures may be subject to change according to the future progress of analysis and study.

Analysis of seismic observation data

TEPCO will continue to gather and sort aftershock records to conduct assessment of seismic motions for confirming seismic safety of the power station in respect to the recent earthquake, and examine seismic motions on the hypothetical free surface of the base stratum on the station premises, with the influence of upper strata analytically removed.

Seismic safety confirmation of important facilities in terms of safety

Seismic motion data used for confirming anti-quake safety in respect to the recent earthquake will be used to assess seismic response analysis and anti-quake safety assessment on important plant facilities in terms of safety.

Future seismic safety assessment

Based on knowledge obtained from the recent earthquake, including findings from active fault probes in sea areas and analysis of seismic observation data, TEPCO will explore future anti-quake safety assessment and items to be reflected to earthquake resistance measures.

This table only shows design values based on dynamic analysis in principle (Design values for the up-down component are omitted as they are based on static design).The design response values (in brackets) for the first floor of the turbine building at Unit 1 are reference figures based on static design.

The Ministry of Economy, Trade and Industry has set up the Chuetsu-Oki Earthquake Investigation and Countermeasures Committee concerning Nuclear Power Facilities” to investigate facts regarding specific impact of the Chuetsu-Oki Earthquake on the Kashiwazaki-Kariwa Nuclear Power Station, and identify future tasks and responses the government and electric utilities must address in reflection of the said Earthquake.
On July 31, the Committee convened its first meeting, and agreed to set up Working Groups to examine specific issues listed below, and deliberate on their findings as the main Committee framework.

Seismic safety assessment based on the knowledge obtained from the Chuetsu-Oki Earthquake

The status of reactor operation management at the time of the Chuetsu-Oki Earthquake, integrity of plant facilities and future response

Information contained in this report will be updated as future detailed investigation by TEPCO makes new findings.

＜References＞　Tokyo Electric Power Company
　　　　　　　　　　 Nuclear and Industrial Safety Agency
　　　　　　　　　　 Nuclear Safety Commission of Japan