Venus-2 PWR engineering mock-up: core qualification and fast neutron field characterization

VENUS-2 is the second stage of the VENUS PWR engineering Mock-up experiment which is part of the Belgian PWR-Pressure Vessel Surveillance Programme, sponsored by the Belgian utilities. Through a cooperation agreement it contributes also, as one of the benchmark fields, to the international LWR-Pressure Vessel-Surveillance Dosimetry Improvement Program supported by the U.S. Nuclear Regulatory Commission. The VENUS-2 Pressure Vessel Mock-up simulates a low-leakage core with the reflector geometry and the core boundary shape of a generic 3-loop power plant. The low leakage configuration is achieved by replacing the eight outer rows of the stainless steel cladded, 4 w/o U-235 enriched, UO2 fuel pins by mixed-oxide fuel pins having the same diameter and the same cladding but containing 2.7 w/o Pu and 2 w/o U-235 enriched fuel. The comparison of the experimental and the theoretical pin-to-pin power distributions is given in this paper as well as the comparison of computed and measured ex-core fast neutron responses of several threshold detectors. The paper gives also some information on the VENUS-3 programme which is designed to benchmark the PLSA (Partial Length Shielded Assembly) concept. This concept aimed to lower exposure to critical vessel sections, especially at the horizontal weld level