“Standard” pressurized water reactor (PWR) calculation procedures based on two-group diffusion theory are used to compute the relative pin-power distribution in the VENUS-I and VENUS-II benchmark configurations. These two critical lattices simulate PWR cores which have fresh (UO2) and uranium/plutonium (MO2) pins on the core periphery, respectively. The purpose of the study is to establish the accuracy of these methods, which are used to obtain the core source distribution for RPV fluence calculations, by comparing the calculated with the experimentally determined relative power variation. Special consideration is given to the core periphery region, which contributes most heavily to the RPV fluence. It is found that the diffusion calculations agree to within 5 to 10% of the measurements for both the uranium and MO2 cores. It is estimated that this order of source discrepancy will cause only about 5% uncertainty in the computed RPV fluence.