<p>In the design of nuclear reactor cores, as elsewhere, it is important to know the accuracy of the analytical tools (computer codes) which are used. An accurate and effective way of obtaining this knowledge is to compare, for controlled reactor conditions, the measured with the simulated neutron flux distributions. The results of the SORGHUM code, which is used for evaluating methods of controlling large power reactors during and after some prescribed perturbations, were checked by simulating the reactor conditions existing in Pickering Reactor Unit 2 for the wire activation experiments during low power Phase B commissioning. Thermal flux distributions were measured for 13 different configurations of the reactivity control devices of Pickering reactor in two fuel channels Ml2 and K5. The SORGHUM code was used to simulate the conditions in 11 of the 13 experiments. The reactivity devices were represented rather simply by an incremental thermal absorption cross-section only. Some slight adjustment to these cross-sections was found necessary to obtain agreement with experimental results for both channels within a maximum discrepancy of 10%. A reactivity worth was calculated of 20.5 mk for alI adjuster rods and 5.0 mk for zone controllers. This should be compared with the measured values of 20.0 mk and 5.0 mk for adjuster rods and zone controllers, respectively.</p> / Master of Engineering (MEngr)