Implementation Standard Concerning the Tsunami Probabilistic Risk Assessment of Nuclear Power Plants: 2011（AESJ-SC-RK004E：2011）

内容紹介

Remarks

This publication is translated from the original Japanese-language version. Should any misunderstandings or misinterpretations arise here from, the original Japanese version alone is valid.

Forwards

A standard for Procedure of Tsunami Probabilistic Risk Assessment (PRA) for nuclear power plants 2011 has been established and issued by the Atomic Energy Society of Japan (AESJ) through the discussion at the Tsunami PRA Subcommittee under the Risk Technical Committee of the Standards Committee. The standard specifies the requirement which should have the PRA regarding incidents resulting from tsunamis as the initiating events at nuclear power plants during power operation, and the concrete method of filling it as an enforcement standard based on the PRA procedure. The mission of the Standards Committee (SC) and the Risk Technical Committee (RKTC) is the establishment and publication of criteria/guidelines with regard to probabilistic assessment of the risk caused by incidents. In this respect, March 11 of 2011 is the day that should be engraved in the heart of the committee members. The 2011 earthquake off the Pacific coast of Tohoku occurred at 14:46:18 Japan Standard Time on March 11. Approximately in 40minutes, the first tsunami struck the Fukushima Dai-ichi Nuclear Power Station (NPS). Consecutively, other tsunamis rushed one after another, which resulted in the station black out and loss of ultimate heat sink in the units 1-4 of the Fukushima Dai-ichi NPS. Without recovery of the AC power, the reactor cores were seriously damaged and the nuclear fuel melted which lead to the radioactive material release to environment. To make the matter worse, the hydrogen detonation in the reactor building took place which provoked the continuous loss of cooling capability and controllability in the reactor core as well as the spent fuel pool. The SC and the RKTC of the AESJ has announced the press release in light of the serious accident to establish the Tsunami PRA Subcommittee and to develop a standard for Tsunami PRA procedures. It indicates the understanding of the SC and the RKTC that the tsunami risk should be emphasized and developed with the highest priority. Japanese nuclear facilities are subject to external hazard risk, particularly, earthquakes and associated incidents with the earthquakes. The necessity of a comprehensive risk assessment related to both the internal and external events has been recognized. The PRA for nuclear power plants evaluates the safety of a nuclear power plant in a comprehensive and quantitative manner using the probabilistic methodology. As mentioned above, the PRA for nuclear power plants can be roughly classified into two groups according to the characteristics of the initiating events; one for internal events, which result from equipment failure occurring inside of the power generation system and human errors, and the other for external events, which result from earthquakes and fires, etc. The PRA focuses on the events which lead to core damage or large amount of fuel failure, identifies the accident scenarios which result in failure and development of events following the failure, and estimates frequencies of each event and its effect. The PRA methodology has been recognized as the effective means which can support the decision making process in the fields of safety design, operation management and safety regulations. As Japan is one of the countries with frequent earthquakes, a great deal of efforts has been made in the field of seismic research since the early stage. By association, researches on the tsunami generation, propagation and induced damage have been published. The accumulation of seismic research results has been incorporated in the seismic design of nuclear power plants and analytical methods have been improved accordingly and the seismic PSA standard has been published in March 2007. The Regulatory Guide for Reviewing Seismic Design of Nuclear Power Reactor Facilities has been published by the Nuclear Safety Commission in September 2006 in which the residual risk quantification is strongly suggested. The Japan Society of Civil Engineers issued a report that sets up the reevaluation of design tsunami height of the nuclear power plants. To our regret, the PRA procedures guide for tsunami has not yet been developed although the importance is held in mind of the PRA community. Accordingly, we hereby institute a standard to specify the standardized procedure for tsunami PRA considering the results of investigation into the concept, the requirements which should have and the concrete fields methods regarding tsunami PRA referring the opinions of experts in the associated fields.