Press Release
Compilation of Data concerning Faults and Other Geological Features around the Hamaoka Nuclear Power Station(Report based on Directive from the Nuclear and Industrial Safety Agency of the Ministry of Economy, Trade and Industry)
May 31, 2011
Chubu Electric Power Co.,Inc.
In view of the fact that significant crustal changes have been observed as a result of the Great East Japan Earthquake, based on a directive received from the Nuclear and Industrial Safety Agency (NISA) of the Ministry of Economy, Trade and Industry,*1 in proceeding with an evaluation of the seismic safety of the Hamaoka Nuclear Power Station with reference to NISA's new Seismic Regulatory Guide, Chubu Electric Power Co., Inc. has compiled data concerning faults and other geological features around the station, and has today presented NISA with a report concerning this data.
1 Content of Nuclear and Industrial Safety Agency directive
In view of the fact that significant crustal changes have been observed as a result of the Great East Japan Earthquake, compilation of data concerning faults, geomorphological displacement,*2 lineaments,*3 etc. extracted from geological surveys previously conducted by the operators of nuclear reactors, etc. and literature reviews, and presentation of data essential to the examination of the possibility that faults must be taken into consideration in the seismic design of nuclear power stations.
2 Report content
In assessing the seismic safety of the Hamaoka Nuclear Power Station, Chubu Electric Power Co., Inc. conducted a survey of faults and other geological features around the facility, and evaluated their effect on it. Judgments were made on this basis as to whether it was necessary to consider individual faults, etc. from the perspective of seismic design. This report compiles the essential information drawn from our report concerning the evaluation of the seismic safety of Hamaoka Nuclear Power Station with reference to the new Seismic Regulatory Guide and materials that have been deliberated on by government working groups up to the present.
(1)Data was compiled concerning faults and other geological features (faults, geomorphological displacement, lineaments, etc.) around the Hamaoka Nuclear Power Station that will not be taken into consideration in seismic design based on surveys conducted up to the present.
(2)Based on the relationship between these faults, etc. and the surrounding stress fields,*4 we do not judge them to be active, and, in addition, the effect of the crustal changes caused by the Great East Japan Earthquake on the stress fields around the Hamaoka Nuclear Power Station was small. We will work to compile data concerning this earthquake, and will appropriately reflect any new findings in future evaluations.
(3)An earthquake that occurred in the east of Shizuoka Prefecture on March 15, 2011 can be indicated as an earthquake occurring close to the Hamaoka Nuclear Power Station (within a radius of around 100 km) subsequent to the Great East Japan Earthquake. We will also work to compile data concerning this earthquake, and will appropriately reflect any new findings in future evaluations.
*1 Nuclear and Industrial Safety Agency (Ministry of Economy, Trade and Industry) Directive: "Regarding the response to the addition of opinions upon considered by NISA in relation to the report of the evaluation results on seismic safety of existing nuclear power reactor facilities etc. in light of the new Seismic Regulatory Guide for based on the 2011 Tohoku District -Off the Pacific Ocean Earthquake (April 28, 2011, NISA No.4)," issued by the Nuclear and Industrial Safety Agency of the Ministry of Economy, Trade and Industry on April 28, 2011.
*2 Geomorphological displacement: Displacement of features on the earth's surface. The motion of faults can be considered as one cause of this displacement.
*3 Lineaments: When geomorphological features such as abrupt inclines in cliffs or mountain ridges or curves in valleys or mountain ridges are aligned following straight lines or are close to straight lines, this linear feature is termed a lineament. Aerial photographs are studied in order to make out lineaments.
*4 Stress fields: Stress fields express what types of forces are acting on geological strata. With the horizontal direction as the reference, if the force is pushing, the stress field is called a compressive stress field, and if the force is pulling, the stress field is called a tensile stress field. Changes in stress fields are related to the movement of plates, and factors such as the direction and angle of subduction of an undersea plate can be considered as causing changes in stress fields.