The Importance of Anisotropic Scattering in High Energy Neutron Transport Problems

Abstract

Neutronic calcuations for high-energy fusion and spallation neutron sources are of increasing interest. The neutron distributions in reactor blankets or deep within shields is influenced by the elastic scattering which becomes highly anisotropic above 10 MeV expecially for heavy elements. Since cannon cross-section libraries are limited by Legendre expansion, or by their upper energy boundary, or exclude elastic scattering above 20 MeV a special library has been created.

To describe the highly anisotropic scattering of very fast neutrons adequately the transport code ANISN has been improved. Fokker-Planck terms have been introduced into the transport equation which accurately describe the small changes in energy and angle. The new code has been tesyed for a d(50)-Be neutron source in a deep penetration iron problem. The influence of the forward peaked elastic scattering on the fast neutron spectrum is shown to be significant and be handled efficiently in the new ANISN version.