ANALYSIS OF SNUBBER REDUCTION OF SECONDARY HOT LEG IN FAST FLUX TEST FACILITY

摘要

This paper describes analyses to qualify the structural integrity of the secondary hot leg (SHL) dump heat exchanger(DHX) piping system of the Fast Flux Test Facility (FFTF) under seismic loading after a number of seismic snubbers were deleted. A baseline geometric model was developed using ADLPIPE computer code, Version 2E1A, 1984. Several seismic analyses were performed with the number of snubbers reduced to determine a support configuration with acceptable anchor and support loads, as well as acceptable piping stresses. A thermal analysis was performed at an operating temperature of 965 ℉ (518°C) to qualify the piping system after replacing some seismic snubbers with rigid supports. A series of displacements from flow- or pump-induced vibration was measured. These vibrations, on the order of tens of seconds or minutes apart, were not continuous and steady, but were a series of forced displacements that rapidly damped out to zero. A scoping evaluation of the effect of the vibration found that the calculated stress is within limits. Results of the stress analysis of the piping with snubber reduction are qualified in accordance with ASME, Section III, Class 1, requirements. Nearly 67 percent of the snubbers in Loop 1 of the SHL piping system can be eliminated or replaced with rigid struts at the same location and orientation. The effects of inelastic strain accumulation, creep-fatigue damage and interaction, and elastic follow-up are evaluated by comparing these results to those of inelastic analysis. Revised anchor and hanger loads were evaluated by comparing these results to those from the original seismic analysis.