Nuclear Performance of Large Pressurized Water Reactors Controlled by Soluble Poison Page: 4 of 28
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NUCLEAR PERFORMANCE OF LARGE PRESSURIZED WATER
REACTORS CONTROLLED BY SOLUBLE POISON
INTRODUCTION
In order to obtain increased power capability from large pressur-
ized water reactors of fixed thermal-hydrualic design, the maximum-to-average
power density ratio of the core must be reduced, allowing more of the core to
operate close to the thermal-hydraulic design limit. The nuclear contribution
to this maximum-to-average power density ratio can be reduced by employing
non-uniform loading of the fissionable fuel. For example, the JO variation
in an uncontrolled, uniformly loaded, cylindrical reactor may be flattened
substantially by preferential loading in several regions. When a nearly
uniform power distribution is obtained in this manner, it is desirable to
operate at power with a uniformly distributed control technique such as a
soluble neutron poison (boric acid) dissolved in the moderator. If a non-
uniformly distributed control technique such as neutron poison rods is
employed, the improvement in power distribution due to non-uniform fuel
loading could be virtually cancelled. Fuel management considerations which
include cycling (partial core refueling) are considerably easier in cores
controlled by soluble neutron poison because the effects of control rod
programming need not be considered in fuel depletion studies, and, of
possibly greater importance, it is not necessary to find .a new control rod,
program for each non-equilibrium cycle .as well as the equilibrium cycle.
Because .of the elimination of the requirement of matching the non-uniform
loading and fuel cycling to a complicated non-uniform control technique,
there is substantially increased freedom in the possible fuel management
alternatives.
Another advantage resulting from the use of a soluble neutron poison
is the reduction in .the number of control rods,. mechanisms, and associated
control and instrumentaticn.equipment which normally would be employed in a
large PWR core. Since the soluble poison concentration requires a significant
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French, R. J. & Miller, D. L. Nuclear Performance of Large Pressurized Water Reactors Controlled by Soluble Poison, article, September 1, 1963; Pittsburgh, Pennsylvania. (https://digital.library.unt.edu/ark:/67531/metadc871636/m1/4/: accessed April 23, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.