Study Concerning Linkage between Active Faults in Vicinity of Hamaoka Nuclear Power Station (Report Following Directive from Ministry of Economy, Trade and Industry's Nuclear and Industrial Safety Agency)
February 29, 2012
Chubu Electric Power Co.,Inc.
As Chubu Electric Power proceeds with the seismic safety evaluation of the Hamaoka Nuclear Power Station as guided by the new seismic durability guidelines that the Nuclear and Industrial Safety Agency (NISA) is currently implementing, we have been studying the possibility that active faults, etc. are linked. This is to announce that today Chubu Electric Power submitted its report on this matter to NISA in accordance with the NISA directive (Note).
1. Content of NISA directive
NISA requires that utilities operating nuclear power plants study and report the possibility of linkage between inland crust active faults, etc. where those faults are physically separated by approximately 5 km or more and of which it has previously been concluded that no linkage exists. The new study on the possibility of linkage should consider the topography and geological structure formation process (tectonics), state of stress, and so on. If the utilities conclude that there is no linkage between active faults, do not use fault length as estimated from the largest earthquake historically in the region as the major grounds for that conclusion. NISA also requires that, if additional study is needed, the utilities should write and submit a study action plan and report the results of their study as based on this plan as soon as it is concluded.
2. Report content
The active fault evaluation that Chubu Electric Power previously conducted in its seismic safety evaluation already considered geological structures, tectonics, etc., and in those cases where faults were judged to be simultaneously active, they were treated as a single earthquake source fault for the sake of evaluation.
We have now redone the study on active fault linkage, taking geological structures, tectonics, etc. into account, regardless of distance between faults (i.e., whether or not they are approximately 5 km or more apart), with the results showing that there are no combinations of active faults that would newly require consideration of whether they are linked.
Chubu Electric Power will continue to gather information on active fault linkage, and any new knowledge will be properly reflected in future evaluations.
(Note) NISA directive: "Regarding Items to Be Reflected in Seismic Safety Evaluations of Nuclear Power Stations, etc., in Light of Knowledge Learned about Seismic Motion from the 2011 Tohoku-Pacific Ocean Earthquake (Intermediate Summary) (Directive)," (Jan. 26, 2012 NISA Number 1)