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Models of absorbing elements with a promising material for the control organs of nuclear reactors have been tested in the SM reactor -pelleted and powder kernels with different composition based on dysprosium hafnate in a mixture with boron carbide. The neutron fluence with energy >0.1 MeV averaged over a kernel volume was (0.9-1.3)·10 22 cm -2 at the moment the tests were completed for different samples. The temperature at the center of the kernels of the absorber element models during irradiation was 620-1100°C in channel No. 4 and 400-500°C in channel No. 9. The results of the materials science studies show that on the whole the serviceability of the absorbing elements based on pellets and powders of dysprosium hafnate is high.The search for materials for the control organs of nuclear reactors is proceeding in the direction of increasing the effectiveness, reliability, and safety of the materials which remain unchanged over a long period of service. In 2005-2007, a technology was perfected on the basis of the Federal Targeted Program "National Technological Resources," an experimental batch of high-density (7.7 -8.2 g/cm 3 ) pellets based on dysprosium hafnate with 23-75 mol.% Dy 2 O 3 and fluorite single-phase structure was prepared, and the batch was tested in an SM reactor. The permanently high effectiveness due to the presence of two absorbers with 13 daughter isotopes, relatively cheap raw material, high melting temperature (2700°C), and radiation resistance make Dy 2 O 3 ·HfO 2 a promising material (Fig. 1) [1].The absorbing materials (B 4 C, Dy 2 O 3 ·TiO 5 , Dy 2 O 3 ·HfO 2 , and others) in the form of VVER absorbing elements were tested and certified in the high-temperature water circuit VP-3 of the SM reactor with test parameters as close as possible to the operating parameters. This stage is a necessary condition for validating the adoption of a new material.For irradiation in SM, the Nos. 4 and 9 reflector channels with neutron flux (energy ≥0.1 MeV) density 0.32·10 15 and 0.66·10 14 sec -1 ·cm -2 , respectively, were connected to the VN-3 circuit facilities of high parameters [2]. An irradiation facility consisting of six perforated, steel, cylindrical containers 12 mm in diameter and 0.5 mm thick with models of the absorbing elements was placed into the channels. A 100-mm long model of an absorbing element contains an 8.2 mm in diameter and 0.45-mm thick 08Kh18N10T steel shell, sealed by welding on end pieces, and pellet or powder (vibrational compacted mixture of powders, sieve with cell size ≤0.0125 mm), and a 74 ± 1.5 and 40 mm high kernel, respectively, used in real parts. The kernel is compacted in helium-filled cladding by a gas-permeable wad made from a pressed nickel sieve (Fig. 2). A list of the absorbing element models tested and the main characteristics of the kernels are presented in Table 1.We shall examine the models and methods for calculating the neutron-physical conditions of irradiation of absorbing materials in the channels of an SM reactor.A numerical model was created on the ...

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Reactions resulting in the accumulation of 3 He and 6 Li, whose thermal neutron capture cross-section is large, occur under the action of neutron radiation in the beryllium blocks of the MIR reactor core. When a neutron absorber accumulates in the moderator of a reactor, important physical characteristics change: reactivity access, efficiency of safety and control rods, and reactivity effects; in addition, energy release is redistributed. An algorithm for calculating 3 H, 3 He, and 6 Li in each beryllium block of the core has been developed and implemented. This algorithm makes it possible to follow the change in the concentration of these nuclides during reactor operation and shutdown. The 3 He and 6 Li concentrations are used as initial data for calculating the neutron-physical characteristics of the MIR reactor using the MCU and BERCLI programs. The computational results for the effect of the accumulation of the nuclides indicated on the neutron-physical characteristics of the core are presented.