On capabilities and limitations of current fast neutron-flux monitoring instrumentation for the DEMO LFR ALFRED

Among Gen IV projects for future nuclear power plants, Lead cooled Fast Reactors (LFR) seem to be a very interesting solution due to its benefits in terms of fuel cycle, coolant-safety and waste management. The novelty of the matter causes some open issues about coolant chemical aspect, structural aspects, monitoring instrumentation, etc. Particularly hard neutron flux spectra would make traditional neutron instrumentation unfit to all reactor conditions, i.e. source, intermediate, and power range. Identification of new models of nuclear instrumentation specialized for LFR neutron flux monitoring asks for an accurate evaluation of the environment the sensor will work in. In this study, thermal-hydraulics and chemical conditions for LFR core environment will be assumed, as the neutron flux will be studied extensively by means of the Monte Carlo transport code MCNPX. The core coolant’s high temperature drastically reduces the candidate instrumentation, because only some kind of fission chambers and Self Powered Neutron Detectors can be operated in such an environment. This work aims at evaluating the capabilities of the available instrumentation (usually designed and tailored for Sodium cooled Fast Reactors, SFRs) when exposed to the neutron spectrum derived from ALFRED, a pool-type LFR project to demonstrate the feasibility of this technology into the European framework. This paper shows that such class of instrumentation does follow the power evolution, but is not completely suitable to detect the whole range of reactor power, due to excessive burn-up, damages or gamma interferences. Some improvements are possible in order to increase the signal-to-noise ratio, by optimizing each instrument in the range of reactor power, such to get the best solution. The design of some new detectors are here proposed, together with a possible approach for prototyping and testing them by means of a fast reactor.