Probabilistic Seismic Demand Model and Seismic Fragility Analysis of NPP Equipment Subjected to High- and Low-Frequency Earthquakes

Abstract

This study presents the Probabilistic Seismic Demand Model (PSDM) and explores optimal intensity measures (IMs) for nuclear power plant (NPP) equipment when subjected to ground motions having high-frequency (HF) and low-frequency (LF) contents. To this end, the PSDM is first constructed in terms of the IM and the corresponding engineering demand parameter, and its outcomes are utilized to select the optimum IMs based on the satisfaction of certain essential properties (i.e., efficiency, practicality, and proficiency). Regarding earthquake excitation, different IMs (i.e., structure-independent and structure-dependent IMs) are studied. The results show that the most appropriate IMs for the seismic performance of the cabinet are velocity spectrum intensity and spectral accelerations for the structure-independent IMs and the structure-dependent IMs, respectively.

Moreover, fragility analysis is performed to assess the vulnerability of NPP equipment. The outcomes indicate that the cabinet is highly vulnerable to HF earthquakes as a consequence of response amplification. In addition, the selection of the earthquake IM has an important influence on the collapse capacity of the cabinet, and the fragility curves obtained from structure-dependent IMs are more reliable in comparison to those of structure-independent IMs.

Keywords:

• Cabinet facility
• cloud analysis
• Probabilistic Seismic Demand Model
• structural demand measure
• optimal intensity measure

APPENDIX

Details of selected earthquakes are given in Tables A.I and A.II.

TABLE A.I High-Frequency Earthquakes

TABLE A.II Low-Frequency Earthquakes

Acronyms

ASI:	=	acceleration spectrum intensity
DM:	=	demand measure
DSI:	=	displacement spectrum intensity
EDP:	=	engineering demand parameter
FB:	=	front-to-back
FEM:	=	finite element model
HF:	=	high frequency
IM:	=	intensity measure
LF:	=	low frequency
LS:	=	limit state
NPP:	=	nuclear power plant
PGA:	=	peak ground acceleration
PGD:	=	peak ground displacement
PGV:	=	peak ground velocity
PSDM:	=	Probabilistic Seismic Demand Model
SS:	=	side-to-side
VSI:	=	velocity spectrum intensity

Nomenclature

$B$ =	=	practical factor
$e_i$ =	=	residual between the actual value and the predicted value
$f_{exp}$ =	=	natural frequencies from the experimental test
$f_{num}$ =	=	natural frequencies from the numerical model
$M$ =	=	magnitude
$N$ =	=	total number of samples
$R$ =	=	distance from the source to the site
$S_a\left(T_1\right)$ =	=	spectral acceleration at $T_1$
$S_d\left(T_1\right)$ =	=	spectral displacement at $T_1$
$S_v\left(T_1\right)$ =	=	spectral velocity at $T_1$
$S_a^{10}$ =	=	spectral acceleration at $T_{10}$
$S_d^{10}$ =	=	spectral displacement at $T_{10}$
$S_v^{10}$ =	=	spectral velocity at $T_{10}$
$S_a^{4-16}$ =	=	spectral acceleration at the frequency range (4 to 16 Hz)
$S_v^{4-16}$ =	=	spectral velocity at the frequency range (4 to 16 Hz)
$S_d^{4-16}$ =	=	spectral displacement at the frequency range (4 to 16 Hz)

Greek

${\beta }_{\mathrm{D}\mathrm{M}|\mathrm{I}\mathrm{M}}$ =	=	standard deviation/efficiency factor
$\zeta$ =	=	proficiency factor
$\mathrm{\Phi }\left(.\right)$ =	=	standard normal cumulative distribution function

Acknowledgments

This work was supported by the Korea Institute of Energy Technology Evaluation and Planning and the Ministry of Trade, Industry & Energy of Korea (number 20171510101960) and by Gwangju University (KR) [2021].