Advances in Nuclear Data Development for Moderator and Reflector Design at the European Spallation Source

Thermal neutron scattering data for neutronic design of neutron sources traditionally has been limited to a few selected materials due to the relevance of those materials to nuclear energy applications and the limitations of legacy software. With the availability and development of recent software, such as NCrystal, the European Spallation Source is engaged in activities to develop new nuclear data, in particular with applications in cold, very-cold and ultra-cold neutrons sources in mind. In this work we showcase highlights of progress on selected studies related to this effort. In particular, we highlight new scattering kernels for Monte Carlo simulation in superfluid helium around 1.0 K and updates to PHITS to include improved thermal neutron scattering.