In the framework of activation calculations of accelerator components with Monte Carlo methods, an unsolved problem is to take into account the spallation products of trace elements and impurities in a bulk material. Because of the low probability of spallation reactions with these elements, a large number of primary particles are necessary to obtain some information about their spallation products. A new algorithm for treating high-energy reactions has been implemented into MCNPX 2.5.0 to overcome these deficiencies. With this algorithm, spallation reactions of all constituents of a material will be performed at each high-energy interaction. This leads to the production of spallation products from all elements in a material. We will present examples of how this new methodology influences the outcome of activation calculations.