Preliminary findings and lessons learned from the 16 July 2007 earthquake at Kashiwazaki-Kariwa NPP - 'The Niigataken Chuetsu-Oki earthquake', Kashiwazaki-Kariwa NPP and Tokyo, Japan, 6-10 August 2007. Mission report. V. 2

Upon request from the Government of Japan an IAEA expert mission was conducted at the Kashiwazaki-Kariwa NPP following a strong earthquake that affected the plant on 16 July 2007. Thus, the mission complemented the ongoing safety evaluations of the incident as they are currently being performed by Japan's Nuclear and Industrial Safety Agency, Japan's Nuclear Safety Commission and the plant operator, the Tokyo Electric Power Company. The scope of the mission was limited to three subject areas: Area 1: Seismic design basis - design basis ground motions Preliminary investigations of the actual earthquake and its ground motions and comparison with the design basis ground motions for the plant seismic design. Area 2: Plant behaviour - structures, systems and components Observation of the damage that occurred as a consequence of the earthquake of 16 July 2007 to the seven units at Kashiwazaki-Kariwa nuclear power plant site on the basis of the information gathered and made available by TEPCO and by performing limited but representative plant walkdowns. Area 3: Operational safety management Preliminary investigations of the operational safety management response and releases of radioactive material during and after the earthquake, on the basis of the examination of documents and of discussions with TEPCO. The mission report is composed of two volumes, Volume I and Volume II. This Volume II contains all supporting documentation and information collected during the mission and provided by the counterpart to the IAEA Expert Team. It is arranged in a way that it will be relatively easy for the reader to find the necessary information. There is a significant amount of information contained in Volume II that has come from different sources and that has been gathered for different purposes. The information has been compiled under headings that indicate its origin and purpose as well as their relationship to the observations and topics discussed in Volume I. First, a few photographs are presented that give the impression of the way the mission was conducted and showing the atmosphere of the mission, such as the meetings and encounters with the media. The preparatory meeting held at the hotel in Nagaoke, upon arrival on Sunday, is portrayed in the first photograph. The arrival at Kashiwazaki-Kariwa NPP on Monday and the encounter with the media and the technical meetings at the plant are shown in the next three photographs. The interest of the media to this event is also shown in the next two photographs taken at the exit of the meetings in the plant and in Tokyo. In the last photograph the IAEA expert team is shown at the hotel after delivery of the draft mission report to Japanese authorities. Subsequently, Volume II is organized in the following way: 1. Part I: BACKGROUND. First of all, there is a significant amount of information provided by NISA, JNES and TEPCO as general background. This information mainly relates to Japanese regulations and general data about the Kashiwazaki-Kariwa NPP and does not pertain specifically to the 16 July 2007 event. All this information is presented under the title of 'Background' and it is not necessarily referenced to any particular discussion area of the mission. 2. Part II: INFORMATION SPECIFIC TO THE THREE AREAS COVERED BY THE MISSION AS SUPPLIED BY THE JAPANESE COUNTERPART. Secondly, there is information supplied by the Japanese counterpart as information specifically relevant to the purpose of the mission, that is, the 16 July 2007 Niigataken Chuetsu-oki earthquake and in general the plant response to this event. This information includes the presentations made by counterpart specialists at the beginning of the mission and also their response to the queries raised by the IAEA team members during the course of the mission. These presentations and the responses are presented under the three discussion areas A1, A2 and A3. If a presentation or response pertains to more than one area this is also indicated. 3. Part III: INFORMATION SPECIFIC TO THE THREE AREAS COVERED BY THE MISSION AS COMPILE D BY THE IAEA EXPERTS TEAM. Finally, there is the third category of information which was compiled by the IAEA team members during the mission. These are photographs that have been taken either by team members themselves (with the explicit permission of the Japanese counterpart organizations NISA and TEPCO) or by TEPCO engineers following the request of the IAEA expert team. Some have been taken to illustrate a technical point during walkdowns and these are linked again to the three areas of discussion A1, A2 and A3