The fragments produced in nuclear reactions for accelarator driven systems (ADS) operation form elements that can have effects on the structure of the reactor. In this regard, the calculation of fragment distributions gives important information for the development of ADS. To obtain those distributions, the Monte Carlo (MC) method is an important tool, and in this work we describe calculations of fragment distributions through a MC code for reactions initiated by intermediate- and high-energy protons and photons on actinide and preactinide nuclei. We study the production of fragments through spallation and fission reactions. The results show good qualitative agreement with experimental data. 1. Introduction The accelerator driven system (ADS) is an innovative reactor which is being developed as a dedicated burner in a double strata fuel Cycle to incinerate nuclear waste [1–4]. The ADS system consists of a subcritical assembly driven by accelerator delivering a proton beam on a target to produce neutrons by a spallation reaction. The spallation target constitutes at the same time the physical and the functional interface between the accelerator and the subcritical reactor. For this reason it is probably the most innovative component of the ADS, and its design is a key issue to develop ADS. The performance of the reactor is characterized by the number of neutrons emitted for incident proton, the mean energy deposited in the target for neutron produced, the neutron spectrum, and the spallation product distribution [5]. The detailed design of spallation neutron sources or accelerator-driven systems (ADS) requires reliable computational tools in order to optimize their performance in terms of useful neutron production and to properly assess specific problems likely to happen in such systems. Among those problems are the radioactivity induced by spallation reaction and the problem of shielding [6] the radiation due to energetic particles generated in the reaction, the changes in the chemical composition and radiation damage in target, window, or structure materials [7], and induced radiotoxicity within the target [8] due the production of several nuclides. Radiation damage can arise from gas production that causes embrittlement of structural materials and from atomic displacements (DPA) which fragilize the various components of the spallation source. Modifications of the chemical composition of these materials possibly result into problems of corrosion or alloy cohesion and modification of mechanical properties because of the appearance of compounds not
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