PSI - Issue 60

Rahul Mittal et al. / Procedia Structural Integrity 60 (2024) 535–540 Rahul Mittal/ StructuralIntegrity Procedia 00 (2019) 000 – 000

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Fig. 2. (a) 3D view of 700 MWe Main PHT system; (b) Typical Arrangement of Snubber on Nuclear Equipment. carried out at stipulated intervals during the service life of the plant . The first ISI interval is 5 year period from the start of operation and subsequent ISI interval is 10 years. The quantum of inspection is distributed evenly as far as practical . Snubber testing and inspection activity contributes to a considerable man-rem consumption during BSDs. Therefore, efforts have been made to reduce number of snubbers to the extent possible by optimizing the piping layout and piping/equipment supporting arrangement. Design provisions have been made for easy and fast removal of snubbers from field and re-installation back to the field. ISI of snubbers include visual examination and functional testing of snubbers. Visual examination of all snubbers is carried out for corrosion, erosion, mechanical damage/deformation, leakage on snubber and snubber supporting arrangement. This also includes visual and surface examination of all welds connecting snubber bracket to snubber support structure. The functional testing of snubbers include free operability check, drag force measurement and sensitivity test . Functional parameters are checked with respect to acceptable values in-line with ISI manual / supplier recommendation. Drag force of the snubbers shall be within 2% of rated capacity/OBE rating. For mechanical snubber, locking acceleration shall be less than 0.02g. For Hydraulic snubbers, locking velocity shall be within 2-6 mm/sec. If any abnormality/unacceptable behaviour observed during inspection, root cause analysis for the deviation from acceptable behaviour is carried out and suitable corrective actions are. Corrective action may be either replacement of faulty snubber with new healthy snubber or overhauling of snubber & re-installation back after successful demonstration of all functional testing. 4. Snubber Health Monitoring System in Indian PHWRs In newer PHWR units (700 MWe PHWRs) and in older PHWR units where mechanical snubbers are being replaced with hydraulic snubbers, an online snubber health monitoring system is being implemented to ensure proper snubber functioning during plant normal operation and to indicate possible malfunction of the snubbers. Snubber health monitoring system includes suitable instrumentation for monitoring snubber travel and oil leakage, which indicate proper operability of the snubbers in the control room and give prompt indication of malfunction of snubbers. Snubber health monitoring system is already commissioned for 700 MWe unit at KAPP-3&4 and operational at KAPP-3.