Analysis of the. flux contribution to the In-Core neutron flux measurements in Material testing Reactors

Neutron flux measurements are always performed in (gamma,n) mixed field especially in the core of a Material Testing Reactor (MTR) where the both fluxes are generally of the same order of magnitude. Therefore, the contribution of the. particle has to be taken into account in the sensor design or in measurement methods for minimizing their impact or correcting it. The latter is necessary to be evaluated for an accurate measurement of the neutron flux in perturbed areas where the ratio of the two kind of particle fluxes are strongly variating in time or in space. It is encountered for example in the transition zone between the core and the reflector or in some low power reactor dynamic states. In addition,. energy spectra and level are usually evaluated with a coarse uncertainty by modelling tools, even if some recent upgrades have been done in this domain in terms of modelling and measurements. After a review of the g spectrum main features in MTR, the different reference techniques applied to the measurement neutron flux (dosimetry, fission chamber, Self-Powered Neutron Detector (SPND)) and their performances and limitations in terms of. sensibility are analysed. Based in the expertise of the CEA and JSI teams, propositions of combining of existing measurement methods and modelling results are proposed to optimize the measurement process, in particular for comparison with calculations.