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The methodological and practical approaches to realizing an iterative multiple-criterion analysis for evaluating the decommissioning costs of the power-generating units of nuclear power plants and the optimal structure of the analysis using information technologies are examined. The objective prerequisites which have been established and facilitate the development and use of decommissioning simulation models in practical work are analyzed.The preparation for and performance of the decommissioning of the power-generating units of nuclear power plants is a complex process consisting of several stages at which the local (objective) concept and program for decommissioning are developed and comprehensive engineering and radiation examinations, decontamination, and equipment disassembly as well as handling of radioactive wastes are performed. At any stage of the decommissioning process, the adoption of validated solutions can be guaranteed exclusively by the presence and completeness of the information required for these purposes. Seventeen power-plant units have exhausted their nominal service life (30 years for domestic units) or are close to doing so and four units -the first two units of the Beloyarskaya and Novovoronezh nuclear power plants -have been shut down and are being prepared for decommissioning. General shutdown of the power-generating units of the nuclear power plants is expected after 2016. The No. 3 and 4 units at the Novovoronezh, the No. 1 and 2 units at the Kola, the No. 1 and 2 of the Leningradskaya, and three units at the Bilibino nuclear power plants will have exhaustd their extended service lives before 2020.The decommissioning of a unit at a nuclear power plant is a large-scale organizational and technical process in many ways comparable in terms of the time, financial, and labor resources required to build the unit. The main problems of decommissioning are reprocessing and removal for subsequent storage or disposal of radioactive wastes which will be produced during the disassembly of the reactor and the power-generating unit. One of the greatest dangers arising during equipment disassembly is exposure to radiation, since protective safety barriers are dismantled deliberately and a large amount of radioactive substances in solid, liquid, and gaseous form and in as aerosols can migrate outside the confines of the units. Handling radioactive wastes and radiological safety are the largest components of decommissioning costs.Considering the duration, complexity, danger to the workers, population, and environment, the high cost, as well as the development of modern information technologies developed using three-dimensional simulation and databases for

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A method for obtaining computational estimates of the radiation characteristics of irradiated structures in RBMK reactors is described. It is based on the MCNP computer program for calculating the spatial distribution of the neutron flux density inside the shaft. The nuclear transmutation occuring in the materials of the structures under irradiation in the reactor and during the subsequent holding period is simulated by the CHAIN program for calculating the isotopic composition and the radiation characteristics on the basis of the MCNP fluxes. Some results of a calculation of the radiation characteristics of the structures in the reactors in the No. 2 and No. 3 units of the Leningrad and No. 1 unit of the Chernobyl nuclear power plants are presented. Estimates of the total activity of the reactors structures and the dose rate near individual components are presented. The distribution of the mass of the structures over the degree of radioactivity is obtained as a fucntion of the holding time of a unit.The first power-generating units with RBMK reactors in the first series of Russian nuclear power plants have now exhausted their nominal service life. Even if the decisions made to prolong the service life above the period intended, the final shutdown and decommissioning of these units is not far in the future. Ukraine, which shut down all three units at the Chernobyl nuclear power plant with RBMK reactors, is already now facing the practical implementation of a program for decommissioning the plant.An RBMK reactor consists of graphite masonry mounted on a metal structure. Fuel assemblies and the control and protection organs are placed in vertical channels inside the masonry. The exterior part of the masonry functions as lateral and end reflectors. Metal structures at the top (scheme E) and bottom (scheme OR) and a lateral cylindrical casing (scheme KZh) seal the reactor space. The bottom support blocks and the top protective plates and the serpentinite fill in the schemes E and OR, together with the water-filled cylindrical side tank, serve as the radiation protection [1].The main reactor components which are activated during reactor operation are the masonry graphite and the pipes in the technological channels, the channels of the control and protection system, the reflector cooling pipes, and the components of the surrounding metal structures facing the core (Fig. 1, Table 1).When one power-generating unit is decommissioned, the radioactive materials which need to be reprocessed and disposed of contain about 1910 tons of radioactive graphite and 2310 tons of activated metal structures from the reactor. The large volume and the great diversity of the materials which need to be stored for a long time change the problem of han-