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Commercial production of 60 Co is being conducted at the Leningradskaya nuclear power plant by irradiating 59 Co in special facilities loading into an RBMK core (in all four units). The computational means used to determine the activity of cobalt in the irradiation setups and to decide when to extract them are described. The particularities of the computational model used for the core, which takes account of the reloading of the fuel assemblies and irradiation setups during fuel burnup, are described.A channel reactor, such as RBMK-1000 in the Leningradskaya nuclear power plant, provides extensive possibilities for producing not only electricity and heat but also special-purpose radionuclides to be used in different industrial applications. For this, targets with isotopes -precursors of the special-purpose nuclides -are irradiated in special setups.For industrial production, it is necessary to know the radioactivity of the extracted isotope, which is the acceptance criterion of the product and determines its price. As a rule, the activity is determined by means of expensive and laborious experimental methods -sectioning the targets in hot boxes. The prediction and knowledge of the computed activity of special-purpose isotopes in specific irradiation facilities makes it possible to decide when to extract the isotopes and correctly plan the disassembly of the setup and packing ampuls of 60 Co, for example, with the required activity in shipment containers. To solve these problems, a program system, which is a necessary element of the technological chain of cobalt production, has been developed at the Leningradskaya nuclear power plant.A channel reactor with regular reloading of fuel assemblies and irradiation setups has certain advantages for obtaining the special-purpose isotopes. However, irradiation occurs in a constantly changing environment (reloading fuel assemblies, motion of control rods, power change, and so forth). The computational model of the reactor core that is used to determine the accumulation of cobalt must take this into account. The software tracking the production of special-purpose isotopes must also correctly determine the rate of the neutron absorption reaction in irradiation facilities with complex structure, and the reaction cross sections of the irradiated materials have, as a rule, a resonance structure.Computational Model of the Core. A neutron-physical calculation of the core of a nuclear reactor is performed using a standard two-step scheme of the homogenization method. The neutron-physical characteristics of various types of cells comprising the core are calculated first for different parameters characterizing the state of a cell. For the cells of an RBMK core, these parameters are the density and temperature of the fuel and graphite and the fuel burnup. When calculat-

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