Extended set of activation monitors for NCT beam characterization and spectral conditions of the beam after reactor fuel conversion

•Conversion from HEU to LEU has only no impact on the spectral characteristics of BNCT beam.•Neutron flux after conversion is comparable with the flux before the conversion.•ZN64G, GA71G, AS75G, PD110M, AG109M, SB121G, SB123G reaction are promising for beam monitoring.

Since 2010 the LVR-15 reactor has been gradually converted from highly enriched fuel (36 wt% 235U) to low enriched fuel with the enrichment of 19.75 wt% 235U. Paper presents influence of the core pattern changes on the neutron characteristics of the epithermal beam. The determination of neutron spectrum free in the beam was done with a set of neutron activation monitors. After the reactor conversion the change in neutron spectrum is not provable as differences are in the range of measurement errors.