PRELIMINARY SEISMIC FRAGILITY ANALYSIS OF SELECTED HEAVYCOMPONENTS IN LNNP UNIT 1 REACTOR BUILDING

摘要

The paper studies the fragility of heavy components in Leningrad Nuclear Power Plant unit 1 reactor building. Theanalyzed components are: (1) drum separators (4 pcs); (2) main coolant pumps (8 pcs); (3) suction headers (2 pcs); (4)pressure headers (2 pcs); (5) refuelling machine (1 pcs). The reactor stack was excluded from the analysis based on thestudy of structural drawings of reactor stack and supporting metal structures. It was judged that the multitude (1693 pcs)of channels in reactor core and adjacent small bore piping ( 50 mm and 70 mm) forms a structure, which inherently hasseismic capacity and damping. The fragility of a component is defined as the conditional probability of its failure givena value of the response parameter, such as stress, moment, and spectral acceleration, peak ground acceleration [1].Using the lognormal-distribution assumption, the fragility (I.e., the probability of failure, f') at any nonexceedenceprobability level Q can be derived as f'=Φ[(ln(a/(_A) +βUΦ-1 (Q))/βR] where Q = P(f < f'|a) is the probability that the conditional probability f is less than f' for a peak ground acceleration a.(_A) is the median ground acceleration capacity, βR is the logarithmic standard deviation representing the inherentrandomness about A, and βU is the logarithmic standard deviation representing the uncertainty in the median value. Thequantity Φ(.) is the standard Gaussian cumulative distribution function, and Φ-1(.) is its inverse. The stress resultantresponses for the investigated heavy component supports are evaluated for drum separator, main coolant pump, suctionheader, pressure header, and refueling machine. For the purpose of defining fragility curves, the possible failure modesmust be identified and evaluated. The results of the fragility analysis are the parameters A, βU, βR for selected heavycomponents.