Experimental database on fast-reactor thermohydraulics for computational code verification

Abstract

The results of benchmark experiments on the thermohydraulics of a model fuel assembly and models of targets used in an accelerator-controlled system with a liquid-metal coolant are presented. Calculations performed using the domestic MIF code and foreign codes are compared. The data obtained from experimental studies of the hydrodynamics and heat-exchange in a fast-reactor core cooled by liquid sodium, which were performed primarily at the Physics and Power Engineering Institute over a long period of time, are briefly reviewed. It is shown that the experimental data for use as verification tests need to be systematized, evaluated, and generalized. The analysis shows the degree of completeness of the experimental data and permits making recommendations for performing experiments to fill the existing lacunas.A new system of strict requirements for fast reactors whose most stressed component is the core has been formulated in the last few years [1,2]. The characteristics of this system need to be validated for nominal and non-nominal operating regimes, they must be improved and optimized and made more reliable. Computational studies of the temperature field in a fuel assembly of the Phoenix reactor (France) which were performed at the Physics and Power Engineering Institute (FEI) for a reactor run have shown that the shape-change of the components of a fuel assembly can result in large nonuniformities of the coolant temperature field, large azimuthal nonuniformities of the temperature of fuel elements, and substantial overheating of the fuel-element cladding in the region of local breakdown of the lattice geometry [3].Effective procedures have been developed for simulating core thermohydraulics -a model of a porous body, channel-wise procedure, simulation of local characteristics of the coolant velocity and temperature fields taking account of heat exchange with fuel elements (solution of the conjugate problem of heat exchange). Unfortunately, it is first necessary to systematize, analyze, and evaluate the experimental data on the thermohydraulics of cores and then to construct on this base verification thermohydraulic tests and to prepare standard problems. Benchmark Experiments on Thermohydraulics Performed at the Physics and Power Engineering InstituteBenchmark experiments on a model fuel assembly with liquid-metal coolant. The experimental studies of the temperature and velocity fields were performed on a model fuel assembly with a nonuniform lattice, which consisted of 25 fuelelement simulators placed in square-packing arrangement with relative step s/d 1 = 1.25 and s/d 2 = 1.46 and consisting of two subzones of fuel-element simulators with different diameters (d 1 = 14 mm and d 2 = 12 mm) and with different heat flux (q 1 and q 2 , respectively) [4] (Fig. 1). The simulators were placed inside a rectangular shell mounted in a cylindrical housing.