 Seismic Safety Division |
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The Seismic Safety Division addresses the improvement of seismic safety of nuclear installations through the cross-check analysis of seismic adequacy and structural integrity, analysis of accidents and troubles, seismic risk evaluation, support for preparing safety standards, and the development of seismic safety analysis codes and earthquake-resistance tests. |
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| Comprehensive Evaluation and Confirmation of Seismic Safety |
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The Division conducts an extensive analysis and evaluation of events caused by an earthquake, including earthquakes/earthquake ground motion and tsunamis, soil stability, and the integrity of buildings/equipment/systems giving consideration to aging, so as to confirm the seismic safety of nuclear installations in the cross-check analysis or accident/trouble analysis. The Division conducts the seismic risk evaluation and also supports the government in the preparation of standards for seismic safety. Furthermore, it takes comprehensive measures for ensuring the seismic safety by linking the software to the hardware including the development/maintenance of analysis codes needed for conducting the analytical evaluation and implementation of earthquake resistance tests. (Figs. 1 and 2)
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Fig. 1. Missions of the Seismic Safety Division
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Fig. 2. Outline of the evaluation of seismic safety of a nuclear power plant
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| 1. Safety analysis including the cross-check analysis of seismic safety |
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Condition in which a tsunami is advancing through the Sea of Japan
Fig. 3. Tsunami analysis
(1983 Nihonkai Chubu Earthquake Tsunami)
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At the stage of the safety review of nuclear installations by the government, the Division conducts JNES's own analysis and evaluation of anticipated earthquakes to be used for evaluating the seismic safety, the strength of earthquake ground motion at the site, soil stability, and the earthquake-resistance strength of equipment to confirm the seismic safety of nuclear installations. Furthermore, it checks the adequacy of analysis results conducted by the licensees, and reports to the government about the results of the cross-checking. It also does the same kind of confirmation for tsunami. (Fig. 3)
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| 2. Investigation of causes for accidents/troubles due to earthquakes and development of measures against them |
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Fig. 4. Analysis of ground motions due to the Niigata-ken Chuetsu-oki Earthquake
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When an accident/trouble occurs in nuclear installations at the time of an earthquake or tsunami, the Division investigates the causes for the accident or trouble according to the latest scientific knowledge and analysis code, and confirms the effectiveness of measures to be taken for preventing its recurrence. Thus, it supports the government in the development of safety regulations. With regard to the Niigata-ken Chuetsu-oki Earthquake occurred in 2007, the Division analyzed the cause of strong ground motions observed at the Kashiwazaki-Kariwa Nuclear Power Station of the Tokyo Electric Power Company exceeding largely the design-basis ground motion, and reported the result to the NISA, National Government. (Fig. 4)
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| 3. Evaluation of seismic risks and measures for improving seismic safety |
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The Division evaluates the risk of nuclear installations against an earthquake or tsunami by means of the probabilistic method, and confirms the effectiveness of such a measure to be used for reducing the risk. Thus, it contributes to the improvement of the seismic safety.
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| 4. Support for preparing seismic safety related standards |
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The Division supports the government in the preparation of standards needed for developing safety regulations related to seismic safety and structural integrity.
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| 5. Development and maintenance of seismic analysis codes and earthquake-resistance tests |
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Fig. 5. Seismic fragility test of a large vertical pump
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The Division conducts tests and investigations, including earthquake-resistance tests, to understand the strength of earthquake-resistance in important safety-related facilities and installations used over a long period of time. (Fig. 5) It also utilizes test results to develop and maintain analysis codes in which the latest analysis techniques or knowledge is incorporated. Thus, it ensures an accurate evaluation of the seismic safety or structural integrity.
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