Neutron flux and reactivity calculations for an optimized arrangement of experimental facilities in a research reactor

For the planned research reactor FRM II (power 20 MW, unperturbed thermal neutron flux ≅ 8 × 10¹⁴ n/cm² · s in the maximum) the neutron flux and the reactivity change caused by the experimental installations in the D₂O moderator were calculated with the Monte Carlo Code MORSE-K. The program and the method of calculation were verified by comparison of calculated and experimental results of the FOEHN experiment. The reactivity changes of individual components of the experimental installations were studied and found to sum up to about 4%. Additionally, the fluxes at the beam tube exit were estimated. At the exit of a thermal beam tube of 50 cm² cross-section one can expect a neutron flux of about 1 × 10¹⁰ n/cm² · s at the exit of a thermal neutron guide 6 × 10⁸ n/cm² · s and at the exit of a cold neutron guide 1 × 10⁹ n/cm² · s, both neutron guides being coated with Ni-58.