MTR core experiments analysis. Pt. 2

In this work experimental thermal and epithermal flux distributions, reflector saving and bucklings were also measured in specially selected MTR cores. These parameters can also be used to check the capability of reactor codes to predict the behaviour of 20% enriched MTR research reactors. The availability of these data in the international literature is scarce and usually the designer has only the values obtained from the core of an operating research reactor. A 4x4 fuel elements graphite reflected core and 4x5 water reflected core, with almost no introduction of Cd control rods, allowed the measurement of quasi-symmetrical axial and horizontal distribution, well suited to check bidimensional reactor codes. Three 5x5 fuel element arrays, water reflected or partially graphite and/or beryllium reflected were also measured to study the flux behaviour in the reflector. Axial and radial reflector savings and bucklings were obtained by fitting experimental neutron flux distributions. The reflector savings and bucklings obtained were used in a semiempirical two group diffusion equation to approximately predict the reactivity values quoted in the paper MTR Core Experiments - Part I. The measured axial reflector saving for a 4x4 fuel elements graphite reflected core has been compared with calculations performed in Argonne. The observed discrepancy, around 10% is in line with discrepancies found in the calculations of reactivity values in CNEA and suggests problems in the calculation of diffusion constants of the reflector. (Author)