Speaker
Description
The DEMO Oriented Neutron Source DONES is a neutron irradiation facility for experimental tests of DEMO reactor structural materials. It is intended to irradiate the materials at typically 5 - 20 dpa/fpy to damage dose levels of around 50 dpa over 3 years. The neutron fluence on the samples in the specimen
capsules in the High-Flux Test Module (HFTM) is a fundamental parameter for post-irradiation analysis, therefore it should be measured with high precision. We suggest to use neutron activation techniques for this purpose as a robust and scalable method. It provides an absolute measurement of the local neutron fluence and is suitable for the HFTM environment which is characterized by intense neutron and photon fluxes over a long period of operation.
We investigate a set of activation materials which appears to cover the expected neutron energy range in the HFTM. The set consists of iron, cobalt, nickel, yttrium, and gold. The selected dosimetry reactions lead to radioisotopes with half-lives of several months up to a few years so that they would preserve neutron flux information over a year of operation without substantial saturation effects. Initial tests of the measurement method were performed with the cyclotron neutron source at NPI Řež which provides a white neutron spectrum with neutron energies up to 32 MeV. This is less than what is expected in ENS (E n <55MeV), however, it does extend over the threshold energies of all considered
dosimetry reactions. Neutron fluence measurement with neutron activation relies on accurate knowledge of the relevant activation cross sections. A survey of available evaluated data in comparison with experimental data is presented and conclusions on the quality of the considered evaluated data for this purpose are drawn. We have also done a preliminary test of a gamma spectrometry geometry with a high-purity germanium detector for small and highly activated samples which may be applied to analyse the HFTM activation probes.