Advanced foil activation techniques for the measurement of within-pin distributions of the Cu-63(n,gamma)Cu-64 reaction rate in nuclear fuel

摘要

Different foil activation techniques have been used for measuring spatial distributions of the Cu-63(n,gamma)Cu-64 reaction within two pins of a SVEA-96 Optima2 boiling water reactor fuel assembly, at the critical facility PROTEUS. This reaction is of interest because its 1/v cross-section gives it a good representation of the U-235 fission rate. Initially, radial capture rate profiles were measured with mechanically punched copper foils. More detailed profiles were then determined by using a 0.2 mm copper wire spiral (similar to 200 mu m resolution), as well as 5-, 10-, and 20-ring UV-lithography, electroplating, and molding (UV-LIGA) foils (up to a 100 mu m resolution). For azimuthal measurements, apart from manually cut activation foils (into 8 sectors), 8- and 12-sector LIGA foils were used. The highly versatile LIGA foils have the additional advantage of being very easily separated into individual pieces after irradiation without the use of punches or other cutting tools. In order to account for the invasive character of the foil activation techniques, corrections to account for sample perturbations and for self-shielding effects were determined via simplified Monte Carlo (MCNP4C) modeling of the experimental setup. The final results from the various measurements of Cu-63(n,gamma)Cu-64 within-pin distributions have been compared with MCNP computations employing a detailed model of the full SVEA Optima2 fuel assembly. (c) 2006 Elsevier B.V. All rights reserved.