Author : Ala Ayodeji Adebbisi
Degree : M.Sc. Nuclear
Title:
Fuel Utilization
Improvements in Light Water Reactors
Abstract :
The demand for energy is poise to
keep increasing as the world population reaches record heights. This demand
will be met from a mix of energy resources. Cost, environmental friendliness
and mobility are some of the indexes by which power energy sources are often
compared. Although the capital cost of building a nuclear power plant is higher
than that of other types of power plants, its fuel cost is much lower compared
to the others. Different initiatives have been incorporated in light water
reactors since the 70s to reduce these costs components and in turn improve the
overall competitiveness of NPP. E. Fujila et.al in the 80s studied ten possible
strategies of increasing fuel utilization in PWRs and found that there is a
potential of a hypothetical cumulative reduction of 30 in ore utilization. The
quest however continues for the optimum burn-up that will be safe, adaptable to
responsible regulatory requirements, economically attractive, resource and
environment friendly and ultimately lower the cost of producing electricity from
NPPs.
MCNPX was used to simulate fuel rods
of a typical 3411 M\Vt 4-100p PWR operating at 85 full power. The effects of
using fuel rods with enrichment to values between 4.5 to 9.5, axial blanket
made of natural or depleted uranium were studied on burn-up and cycle length.
Increasing the enrichment from 4.5, 6.5 to 8.5 increases the cycle length from
1290, 1630days and 2140days respectively and the burn-up from 32G Wd/MTU, 50
GWd/MTU to 65.25GWd/MTU. A quadratic relationship exists between the percentage
enrichment and the maximum burn-up attained in fuel rods with enrichment
varying from 4.5 to 9.5. Increasing enrichment is more effective in increasing
cycle length from the current average enrichment of 4.5 to 7.5. Increasing
enrichment reduces the efficiency of the burnable absorber and extra radial
reflectors increases the average flux in the peripheral assemblies.
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