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Abstract
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The Integral Pressurized Water Reactors (IPWRs) as the innovative advanced and generation-
III þ reactors are under study and developments in a lot of countries. This paper is aimed at the thermal
hydraulic study of the hot and average fuel sub-channel in a Generation III þ IPWR by loose external
coupling to the neutronic simulation. The power produced in fuel pins is calculated by the neutronic
simulation via MCNPX2.6 then fuel and coolant temperature changes along fuel sub-channels evaluated
by computational fluid dynamic thermal hydraulic calculation through an iterative coupling. The relative
power densities along the fuel pin in hot and average fuel sub-channel are calculated in sixteen equal
divisions. The highest centerline temperature of the hottest and the average fuel pin are calculated as
633 K (359.85 0C) and 596 K (322.85 0C), respectively. The coolant enters the sub-channel with a temperature
of 557.15 K (284 0C) and leaves the hot sub-channel and the average sub-channel with a
temperature of 596 K (322.85 0C) and 579 K (305.85 0C), respectively.
It is shown that the spacer grids result in the enhancement of turbulence kinetic energy, convection
heat transfer coefficient along the fuel sub-channels so that there is an increase in heat transfer coefficient
about 40%. The local fuel pin temperature reduction in the place and downstream the space grids
due to heat transfer coefficient enhancement is depicted via a graph through six iterations of neutronic
and thermal hydraulic coupling calculations.Working in a low fuel temperature and keeping a significant
gap below the melting point of fuel, make the IPWR as a safe type of generation eIII þ nuclear reactor.
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