Katsumi Ebisawa

Failure Probability of Degraded Pipes Based on Probabilistic Fracture Mechanics for Seismic Safety Margin Assessment on NPP

The Niigata-ken Chuetsu-oki Earthquake happened in July 2007. Although the observed seismic ground motions of Kashiwazaki-Kariwa nuclear power plants greatly exceeded their design values, the important functions of the plants such as “shutdown”, “cooling”, and “confinement” were successfully ensured. Therefore, assessment of the seismic safety margin of nuclear power plants, both their systems and their components, becomes a very important issue. In this paper, failure probability of cracked pipes in existing nuclear power plants is analyzed by employing an improved probabilistic fracture mechanical analysis code and considering stress corrosion cracking and fatigue. Based on the analysis results of the failure probability and the definitions of the seismic safety margin, the seismic safety margin of degraded pipes in existing nuclear power plants is investigated.Copyright

Seismic Safety Margin Assessment for Thin-Wall Cylindrical Tanks Utilizing Ultimate Strength Test

In Japan, the Seismic Design Guideline for Nuclear Power Plants revised in 2006 requires that residual risk for earthquakes beyond design base be considered. Moreover, in the Niigata-ken Chuetsu-oki earthquake (NCOE:2007), the earthquake motion exceeded the seismic design condition of the Kashiwazaki-Kariwa nuclear power plants (KK NPPs). In response to these issues, there is a growing demand for quantitative clarification of seismic safety margin. The Japan Nuclear Energy Safety Organization (JNES) started a study on the seismic safety margin. JNES defined the term “seismic safety margin” in this study. The seismic safety margin is based on the probability distribution of seismic response and seismic capacity of equipment. Regarding the seismic capacity, JNES has carried out seismic capacity tests on various types of equipment whose malfunction would significantly affect core damage frequency in terms of seismic probabilistic safety assessment (seismic PSA). Our seismic safety margin is effective to understand the quantitative margin related to the failure of equipment. JNES applied the concept of seismic safety margin to thin wall cylindrical tanks utilizing ultimate strength test results, and compared it with the design margin. This paper reports examples of the seismic margin evaluation of cylindrical tank.© 2010 ASME

Seismic Safety Margin Assessment for Electrical Components Utilizing Full-Scale Test

In Japan, the Regulatory Guide for Reviewing Seismic Design of Nuclear Power Reactor Facilities (2006) requires that residual risk for earthquakes beyond design base be considered. Moreover, in the Niigata-ken Chuetsu-oki earthquake (NCOE:2007), the earthquake motion exceeded the seismic design condition of the Kashiwazaki-Kariwa nuclear power plants (K-K NPPs). In response to these issues, there is a growing demand for quantitative clarification of seismic safety margin. The Japan Nuclear Energy Safety Organization (JNES) started a study on the seismic safety margin. JNES defined the term “seismic safety margin” in this study. The seismic safety margin is based on the probability distribution of seismic response and seismic capacity of equipment. Regarding the seismic capacity, JNES has carried out seismic capacity tests on various types of equipment whose malfunction would significantly affect core damage frequency in terms of seismic probabilistic safety assessment (seismic PSA). Our seismic safety margin is effective to understand the quantitative margin related to the failure of equipment. This paper presents examples of seismic safety margin evaluation. Specifically, JNES has applied the evaluation concept of the seismic safety margin to a metal-clad switchgear and a reactor protection rack utilizing full scale model test results.© 2010 ASME