San Diego, California, 17-19 June 2002

Neutron time-dependent responses in the structural wall of Inertial Fusion Reactors: consequences in radiation damage.

J. M. Perlado, D. Lodi^*, J. Marian^&, A. I. G. Plata, M. Salvador,

L. Colombo², T. Díaz de la Rubia¹

Instituto de Fusión Nuclear (DENIM) / E.T.S.I.I./Universidad Politécnica de Madrid

J. Gutiérrez Abascal, 2 / 28006 Madrid (Spain)

mperladodenim.upm.es

1. Lawrence Livermore National Laboratory (LLNL, USA),
2. University of Cagliari (Italy)

*also SCK CEN MOL (Belgium), ^&also LLNL (USA)

 

Neutron pulses are a key characteristic of materials irradiation in Inertial Fusion Energy (IFE) reactors. That peculiarity can generate a specific response, different from that of steady-state irradiation, when determining materials damage and activation. Heat deposition and tritium production are not influenced by this effect. That certainly depends on the characteristic times corresponding to the pulse frequency versus those of mechanisms to be evaluated.

This work will present new results on the time-dependent neutron fluxes, and associated damage functions, in protected structural walls. Different target calculations have been performed to obtain neutron energy spectra from burnout emissions, with different time-dependent scales. Protections of LiPb and Flibe have been considered with their thickness as a parameter, being the structural wall (steel) assumed as Fe. Neutron Fluxes versus time from target emission will be presented showing the differences between the two protections, due to the differences in density, moderation and threshold reactions such as (n, 2n) and (n, 3n), in the intensity and also in the energy spectra characteristic in time.

Using one of those time-dependent neutron irradiations in the structural wall, we have performed a multiscale modelling study of pulse irradiation in Fe up to the level of defect characterisation depending on time irradiation. A well established procedure is able to include with the appropriate dose rate the cascades generated in time in a kinetic MonteCarlo (KMC) lattice (microscopic) to analyse the defects diffusion, clustering and disintegration. Different impurity concentrations are considered and some modifications in the defect dynamics such as diffusion coefficients and binding energies are discussed. We will remark the established differences with a continuous irradiation for a still low fluence of irradiation. An experimental validation of multiscale modelling approach by using Fe ions on ultra-pure Fe will also be presented. We also will present new results conducting to calculation of defects energetic in SiC (key low activation material), by using a new code based on tight-binding molecular dynamics. The final goal is to understand by the first time diffusion processes in SiC under irradiation.