Non uniform thickness neutron spectrum shifter to fit radiation BB effects on material in IFMIF-DONES

The International Fusion Materials Irradiation Facility – Demo Oriented Neutron Source (IFMIF-DONES) plays an essential role in testing and qualifying materials for the development of nuclear fusion technology. It provides a neutron source capable of reproducing the radiation effects on materials expected in nuclear fusion reactors. The possibility of testing blanket materials behind the high flux test module is being analyzed. A neutron spectrum shifter (NSS) was proposed to modulate the energy of the neutrons with the aim of obtaining radiation effects closer to those expected in the breeder zone of the future nuclear fusion power plant DEMO. For the materials test, it is desirable to obtain a region as large as possible with homogenous neutron field. This article describes the possibility of using a non-uniform thickness NSS for tweaking the output neutrons with the aim of homogenizing the neutron flux and its effects on the irradiated samples. This concept has been tested in the context of an irradiation module for liquid breeder blanket materials. Results show that optimizing the NSS geometry allows tailoring the irradiation conditions, enabling multiple samples to be exposed under the same conditions and improving the statistical relevance of the post-irradiation analysis.