PSI - Issue 60

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

537 3

220 MWe 0 10 20 30 40 50 60 70 Snubber Quantity per Unit Summary of PHT System Snubbers in Indian PHWRs 540 MWe 700 MWe 60 29 8 32

Hydraulic Mechanical

0

8

32

60

29

0

Fig. 1. Summary of PHT System Snubbers in Indian PHWRs.

with feeder pipes connecting coolant channel assemblies to the reactor headers. Summary of snubbers provided in Indian PHWRs is shown in Fig. 1. Continuous efforts have been made to optimize the number of snubbers from older PHWR units i.e. 220 MWe to latest 700MWe PHWR units. Numbers of snubbers have been significantly reduced in latest 700MWe PHWR design. Snubbers have been eliminated/reduced at location which are difficult to access or having harsh environment ex. headers located inside insulation cabinet. At some locations, snubbers have been replaced with rigid supports, guides or limit stops based on detailed analysis to achieve improved layout and decongestion. Optimization of Snubbers on major nuclear equipment viz., SGs, PCPs, S/D HXs and pumps has been carried out. Snubbers in nuclear piping have also been reduced considerably (by about 50%) by optimization of plant layout for 700MWe PHWRs. Reduction in numbers of snubbers helps in reduction in quantum of periodic testing of snubbers and hence, man-rem consumption involved during removal of snubbers from field and re-installation back to the field etc. The PHT system is a high energy system with maximum pressure more than 100 kg/cm2 and maximum temperature above 300°C. It is required to be qualified for all the applicable loads including seismic loads under design condition & various service levels as per the requirements of ASME B&PVC Div-1, section III subsection NB. Mathematical idealisation of integrated nuclear piping along with major nuclear equipment was carried out to predict the operating and dynamic behaviour of the system. Location and required capacity of snubbers was finalized based on the analysis results. The use of snubbers ensures relatively lower operating stresses in connected piping, relatively lower nozzle loads on the connecting equipment, load transfer to civil structure etc. Typical layout of PHT system of 700MWe PHWR is shown in Fig . 2 (a) . Typical arrangement of snubber attached to nuclear equipment is shown in Fig . 2(b) . 3. In-Service Inspection of Snubbers Snubbers installed on main PHT system are safety-related dynamic restraints and hence, require periodic inspection to ensure their proper functioning during normal operation and during dynamic events (e.g. during a seismic event). Periodic functional testing of snubbers is performed in Indian PHWR during plant Bi-annual Shutdown (BSD) as per the ISI schedule of the snubbers. Inspection of Structures, Systems and Components (SSCs) in Indian PHWR units is