Radiation damage to heavy target materials induced by high energy proton and electron beams

Abstract

Nuclear waste transmutation is an important concept in the development of an advanced fuel cycle. Along with reactor-based approaches, waste transmutation using accelerators is being investigated. Currently, the most widely accepted concept for accelerator-based transmutation is with the use of a high-current proton accelerator. There has also been some interest in investigating the efficacy of using electron accelerators for this purpose. In contrast to high-current proton accelerators, electron accelerators use well known technology, that is been used in a variety of other applications. With the availability of high energy electron beams, electron accelerators are capable of producing a high level neutron flux. One of the concerns with the use of high energy particles for neutron generation/waste transmutation is radiation damage to targets and surrounding materials. The proton beam induces spallation reactions in targets which typically results significant radiation damage. Having a much smaller particle mass, electrons would be expected to cause much less radiation damage. With an electron beam, however, the resulting Bremmstrahlung photons will also cause radiation damage. In this study, radiation damage to materials was analyzed both for proton and electron accelerator beams. Materials selected for the study were used target lead and uranium. The MCNP-X code was used for the supporting calculations. Targets were set up in a cylindrical geometry. Details of flux and spectra distributions in the target were characterized for protons and electrons, and for photons and neutrons. With the availability of electron, proton and neutron fluxes and relevant reaction cross sections, the radiation damage products and displacements were calculated by folding the proton or neutron flux data into the corresponding cross section with the source beam assumed at 1mA and 1000MeV. Radiation damage was calculated for 10,000 hours of irradiation. Results indicate that radiation induced displacement typically is more than 30 times greater with the proton accelerator beam than with the electron accelerator beam.

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