D.G. Cepragaa, G. Cambib, M. Frisonic
a) ENEA, Dipartimento Innovazione, Divisione Fisica Applicata, Bologna, Italy
b) Bologna University, Physic Department, Bologna, Italy
c) ENEA, Guest researcher, Bologna, Italy
Tokamak dust characterization is a key issue for the source terms involved in ITER accident sequences. As tungsten is foreseen as protective material for various divertor regions, neutron transport and activation calculations are needed to characterize the tungsten dusts that are produced by plasma erosion, run away electrons and/or plasma disruptions. The paper presents an assessment aimed to point out the impact of the neutron spectra and the activation libraries on the relevant tungsten activation characteristics (the specific activity and the decay heat). The analyses refer to the divertor dome and they are based on the ITER Basic Performance Phase (neutron power load of 1 MW/m2 on the Outboard First Wall equatorial plane). The dome protective material is a 10 mm thick tungsten layer, the heat sink is Glidcop (water cooled). The dome support and the cassette body is in AISI 316LN (water cooled). The integrated radiation transport and activation methodological approach Vitamin-Scale-Anita/Fispact has been applied. The group averaged neutron fluxes are obtained by the Scale transport sequence Bonami-XSDRNPM.
Three aspects impacting on the neutron flux spectra are analyzed.
1) The cross section transport libraries. The Vitamin-C (ENDF/B-IV data), the Vitamin-E (ENDF/B-V data), and the Vitamin-ENEA (ENDF/B-VI data) have been considered. Both the NJOY 91.38 and the AMPX-77 code systems have been applied to process the ENDF/B-VI data.
2) The geometrical model and the material zone homogenization. Two options have been assessed: tungsten as a separate protective layer, or tungsten homogenized with the copper heat sink and the related coolant.
3) The self-shielding treatment to account for the relevant resonances (e.g. the giant resonance of the W-186 isotope). The Bondarenko shielding factor method has been applied, through the Bonami module.
The ANITA-4 and the FISPACT-4 activation codes have been used to evaluate the material activation characteristics. The European Activation File, versions EAF2 and EAF4.1, and the FENDL/A-2 activation data libraries have been considered. A reference pulsed irradiation scenario resulting in a neutron fluence of 0.3 MW-y/m2 on the outboard first wall is used.
The activation results related to the tungsten divertor dome are presented and analyzed to point out the relevant impact of the input data and assumptions.