Proceedings of IC

AP

P 2015

May 03-06, 2015 - N

ice (France)

Paper 15277

NU

ME

RIC

AL S

IMU

LA

TIO

N O

F R

IB-R

OU

GH

EN

ED

FL

OW

IN A

DV

AN

CE

D

GA

S-C

OO

LE

D R

EA

CTO

R

V

ineet Vishw

akarma

1, Sanjeev Kum

ar 2, Arun K

umar Saha

2, Prabhat M

unshi 1, 2 Indian Institute of Technology K

anpur 1N

uclear Engineering and Technology P

rogramm

e, Indian Institute of Technology Kanpur, K

anpur, UP, India 208016

2Departm

ent of Mechanical E

ngineering, Indian Institute of Technology Kanpur, K

anpur, UP, India 208016

Tel: +91-512-25964, F

ax: +91-512-2597408, E

mail: vinvish@

iitk.ac.in

Abstract – T

he present work highlights the num

erical simulation of fully developed flow

and heat transfer over a ribbed fuel pin in the core of a typical A

dvanced Gas-cooled R

eactor. A sim

ple square-ribbed fuel pin, having constant wall heat flux,

has been analyzed under normal reactor running conditions. T

he Reynolds A

veraged Navier-Stokes and energy equations

(unsteady, two-dim

ensional and axisymm

etric) in cylindrical co-ordinates are solved using Marker and C

ell method on a

staggered grid framew

ork. The k-� m

odel is employed to incorporate the effect of sm

all scales of turbulent flow. P

eriodic boundary conditions are used to exploit the advantage of the flow

and heat transfer being fully developed. Simulations are

performed for three rib configurations w

ith different pitch. The re-circulating flow

has been observed, before and after the rib, as expected. F

riction factor and Nusselt num

ber are compared for all configurations. T

he rib configuration with highest

pitch performs better than the other configurations. T

his conclusion is made on the basis of associated low

friction factor and high heat transfer.

I. INT

RO

DU

CT

ION

Advanced gas-cooled nuclear reactors are the second

generation gas-cooled

reactors developed

by U

nited K

ingdom. T

hese successors of Magnox reactor involve

Graphite as neutron m

oderator and pressurized Carbon

dioxide as coolant. They require fuel cladding of stainless

steel to

withstand

higher tem

peratures for

improved

thermal efficiency. H

igher neutron capture cross-section of

the cladding

material

enforces the

requirement

of enriched uranium

fuel whose advantages are high fuel

burn-ups and less frequent refueling. There are currently 7

reactor plants

(each consisting

of 2

reactor units)

operating in United K

ingdom.

There are over 300 fuel elem

ents in the reactor core. E

ight of these fuel elements are linked together vertically

with a tie or guide bar to form

a fuel stringer assembly,

passing through

centers of

fuel elem

ents. E

ach fuel

element is m

ade up of 36 fuel pins cladded with stainless

steel and housed in graphite sleeves, as shown in figure I.

Each fuel pin encom

passes 64 fuel pellets, with each

pellet approximately equivalent to 1.5 tonnes of coal.

All 36 fuel pins along w

ith the central guide tube are supported

by stainless

steel grid

and (tw

o) braces

to m

aintain the spatial arrangement. G

raphite sleeves are the m

ain structural

components

providing support

to pin

cluster and the stringer above it. Usually a fuel elem

ent assem

bly weighs around 85 kilogram

s out of which 28

kilograms are constituted by the graphite sleeve.

Pellets of U

ranium dioxide (U

O2 ) enriched to 2.5-

3.5% are used as fuel. T

he pressurized coolant gets heated by circulating through the core. It reaches approxim

ately 650°C

and passes over the boiler tubes, as illustrated in figure II. T

he rate of nuclear fission is controlled by neutron-absorbing m

aterials called control rods which can

shut-down the reactor. T

here are additional shut-down

systems

called secondary

and tertiary

systems

which

function by nitrogen injection into the coolant and boron spheres injection into the reactor respectively [1].

Figure I - A

n AG

R fuel elem

ent [1]

II. BA

CK

GR

OU

ND

Turbulent flow

over rough surfaces occurs in diverse situations

and is

of huge

significance in

fluids engineering.

It is

one of

the prim

e areas

of fluid