Optimization of Shutoff Rods in a CANDU Reactor

Abstract

<p> In CANDU reactors, mechanical devices called shutoff rods are used to shutdown the reactor if required. These rods are made of high thermal neutron absorbing material such as cadmium. The number and the locations of the shutoff rods are optimized for a given reactor configuration. Optimization here means minimizing the number of rods and maximizing their reactivity depth or effectiveness. </p> <p> Optimization may be studied in various ways but the method selected is both simple and basic. It is apparent that if the interaction effects between the individual shutoff rods are reduced, their worths will increase. The optimum distance between two rods was determined to be 130 cm. Also, the best location of a third rod with respect to two already placed at an optimum separation was studied. Finally, these results were used in order to determine the optimum distance between banks of shutoff rods. These banks of rods were arranged in such a way as to achieve maximum flux flattening with all the rods inserted in the core. A 22 shutoff rod configuration for an adjuster flattened CANDU reactor gave a total change of 5.6% in keff. </p>