Displacement damage quantification in future fusion systems

The demanding neutronic environment in a future fusion power plant will require a thorough understanding of the mechanisms at work in producing displacement damage, their magnitudes, and their effects on the materials and their properties. It is a pre-requisite to have a precise understanding of the Primary Knock-on Atom (PKA) energy spectra caused by 14.1 MeV fusion neutrons in order to have a good foundation for a quantitative determination of the damage driving phenomena produced as a result of neutron encounters. At the higher neutron energies involved in fusion compared to fission, inelastic collisions become very much more significant. This adds to the complexity of estimates of the deposited energy. A Monte-Carlo transport code (MCNP5) has been adapted to provide neutron induced PKA energy spectra for both elastic and inelastic neutron collisions. The introduction of PKA calculations of this type to an MCNP code is new. The Norgett-Robinson-Torrens [M. Norgett, M. Robinson, I. Torrens, A proposed method of calculating displacement dose rates, Nucl. Eng. Design 33 (1975) 50-54] modification to the Kinchin-Pease [G. Kinchin, R. Pease, The displacements of atoms in solids by radiation, Rep. Prog. Phys. 23 (1955) 1-51] model of atomic displacements allows a convenient normalisation measure, the displacements per atom (dpa), allowing for both elastic and inelastic neutron collisions. Application of this work to models of the Power Plant Conceptual Study (PPCS) [G. Marbach, I. Cook, D. Maisonnier, The EU power plant conceptual study, Fusion Eng. Design 63-64 (2002) 1-9] very efficiently generates the PKA spectra and dpa damage as a function of location, providing data that can be used in the design of both power plants and materials testing facilities.