Numerical Modeling of Delayed-Neutron Precursor Transport in a Sodium-Cooled Fast Reactor
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NUMERICAL MODELING OF DELAYED-NEUTRON PRECURSOR TRANSPORT IN A SODIUM-COOLED FAST REACTOR S. A. Rogozhkin,1 S. L. Osipov,1 A. V. Salyaev,1 S. G. Usynina,1 V. I. Pokhilko,2 and M. L. Sazonova2
UDC 621.039.513:621.039.526
Methods of determining the efficiency of the system that controls the seal-tightness of fuel-rod cladding and localizes FA with leaky fuel rods in a fast reactor are examined. It is shown that the design procedure has significant limitations. A procedure for numerical modeling of the transport of delayed-neutron precursors was developed to take account of the special features of liquid-metal coolant flow. A special computational module FV-BN was developed within the framework of the FlowVision software package. The computational results obtained for the concentration distribution of delayed-neutron precursors are transferred into the deterministic transport code TORT in order to obtain the spatial-energy distribution of the neutron flux density in a three-dimensional geometry. The procedure was verified on full-scale reactor problems by simulating the flow-through parts of the upper mixing chamber of the fast reactor.
One of the main protective barriers to the propagation of radioactive substances in a reactor is the fuel-rod cladding, which in its intact state prevents fission products from egressing from the fuel into the coolant. In fast reactors with sodium as the coolant, a special system fulfills the function of controlling the seal-tightness of the fuel-rod cladding. One subsystem of the overall system is a sectoral system for monitoring the seal-tightness of the cladding (SSMTC). The principle of operation of this subsystem is based on recording the radiation of the delayed-neutron precursors – short-lived fission products of the fuel. In the event of “fuel–coolant contact” seal-failure of a fuel rod, aside from gaseous fission products (xenon, krypton) and volatile fission products (iodine, cesium), short-lived fission products egress into the coolant laving the fuel. Then, they are transported together with the sodium flow into the zone of entry apertures of the intermediate heat-exchangers, opposite which, behind the reactor, are situated ionization chambers that record the neutron radiation from the coolant. When the maximum admissible flux density of delayed neutrons and its rate of growth are reached, the SSMTC generates emergency signals that go to the control and safety system. Fuel assemblies with fuel-leaky fuel rods are discovered and localized in the core on the basis of the SSMTC response function. An experimental determination of the response function of ionization chambers requires expensive studies performed using a special methodology on operating reactor facilities. At the same time, a high-quality design of different systems, equipment, and structural elements is necessary for reliable operation. The current status of the computational means and numerical methods for performing calculations makes it possible to use numerical modeling software to solve this problem. On t
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