The
Indian Pressurized Heavy Water Reactor (PHWR) core consists of a number
of horizontal channels containing nuclear fuel bundles.Parallel coolant
channels are connected to Inlet and Outlet header through feeder pipes.
Coolant from Reactor Inlet Header is distributed to the coolant
channels and after removing heat combines at Reactor Outlet Header. Due
to space constraints the feeder pipes are joined to the channel with one
or two elbows close to the end fittings of the coolant channels. The
carbon steel feeder pipes carry high temperature fluid at higher
velocity and are liable to undergo Flow Accelerated Corrosion (FAC). In
the recent inspection it has been found that feeders having double elbow
are more susceptible to FAC on the intrados of second elbow. But it was
found that in some of the elbows maximum thinning due to FAC was
observed on the intrados of the first elbow. Hence to resolve this,
effect of first bend orientation with respect of upstream direction has
been studied. Two different approaches are used for predicting the FAC
rate from calculated value of wall shear stress by CFD. One method is
based on evaluating of wear rate using Colburn analogy and the other
using an empirical equation between wear rate and shear stress. In
Colburn analogy, mass transfer coeflcient is evaluated by knowing shear
stress and equilibrium concentration. For a case study, wall shear
stress obtained from k-E turbulence model was compared with k-w SST
turbulence model and no appreciable change in the wall shear stress has
been found. Hence for subsequent analysis k-E turbulence model was
chosen because large mesh size near to the surface (first layer
thickness) is permitted due to higher y+ value.