Considering the non-linear behavior of structure and soil when evaluating a nuclear power plant's seismic safety under a beyond-design basis earthquake is essential. In order to obtain the nonlinear response of a nuclear power plant structure, a time-domain SSI analysis method that considers the nonlinearity of soil and structure and the nonlinear Soil-Structure Interaction (SSI) effect is necessary. The Boundary Reaction Method (BRM) is a time-domain SSI analysis method. The BRM can be applied effectively with a Perfectly Matched Layer (PML), which is an effective energy absorbing boundary condition. The BRM has a characteristic that the magnitude of the response in far-field soil increases as the boundary interface of the effective seismic load moves outward. In addition, the PML has poor absorption performance of low-frequency waves. For this reason, the accuracy of the low-frequency response may be degraded when analyzing the combination of the BRM and the PML. In this study, the accuracy of the analysis response was improved by adjusting the PML input parameters to improve this problem. The accuracy of the response was evaluated by using the analysis response using KIESSI-3D, a frequency domain SSI analysis program, as a reference solution. As a result of the analysis applying the optimal PML parameter, the average error rate of the acceleration response spectrum for 9 degrees of freedom of the structure was 3.40%, which was highly similar to the reference result. In addition, time-domain nonlinear SSI analysis was performed with the soil's nonlinearity to show this study's applicability. As a result of nonlinear SSI analysis, plastic deformation was concentrated in the soil around the foundation. The analysis results found that the analysis method combining BRM and PML can be effectively applied to the seismic response analysis of nuclear power plant structures.

1. 서 론
2. 비선형 SSI 해석 방법
    2.1 경계반력법
    2.2 Perfectly Matched Layer
3. BRM과 PML을 결합한 SSI 해석
    3.1 해석 모델
    3.2 해석모델의 고유진동수
    3.3 PML 계수의 최적화
4. 비선형 SSI 해석 사례
    4.1 비선형 SSI 해석 모델의 검증
    4.2 설계초과지진 시 비선형 SSI 해석
5. 결 론
감사의 글
REFERENCES

• 이혁주(전남대학교 건축토목공학과 박사과정) | Lee Hyeok Ju (Ph.D. Student, Department of Architecture and Civil Engineering, Chonnam National University)
• 임재성(전남대학교 건축토목공학과 박사과정) | Lim Jae Sung (Ph.D. Student, Department of Architecture and Civil Engineering, Chonnam National University)
• 문일환(한국전력기술 주임연구원) | Moon Il Hwan (Supervisory Researcher, KEPCO E&C)
• 김재민(전남대학교 토목공학과 교수) | Kim Jae Min (Professor, Department of Civil Engineering, Chonnam National University) Corresponding author