The current program in Russia to increase the fuel consumption of fast reactors and increase its burn-out causes the transition to new structural materials, which, in turn, leads to changes in the neutron-physical characteristics of reactors. In particular, the drop in the reactivity reserve noted in the BN-600 reactor of the Beloyarsk NPP at the end of 76 operational cycles, as will be shown below, is due to the transition to a new type of shell steel with an increased content of nickel, which strongly affects the reactivity. Design support for the operation of the BN-600 and BN-800 fast reactors, as well as the experiments carried out on them, is performed by IPPE. This article presents the results of a calculated analysis of the expected changes in the reactivity reserve at the end of 76 operational cycles when replacing the shell steel in BN-600. In addition, the influence of experimental assemblies located in the core on the reactivity reserve of the BN-600 is analyzed. Analysis of calculations of the actual loading of the BN-600 reactor at 76 operational cycle using the methods of the 1st-order perturbation theory, strict perturbation theory, and the Monte Carlo method showed that a partial transition at 76 operational cycle to EK-164 shell steel leads to a decrease in the reactivity margin by 0.030±0.004 %Δk/k. Replacement of steel for the entire core will reduce the reactivity margin by ~0.12 %Δk/k, which is confirmed by Monte Carlo calculations. The calculated reactivity margin obtained at the end of 76 operational cycles for the hot state of the BN-600 reactor is in good agreement with the measured reactivity margin.
The authors propose an approach to the calculation of the levelized unit fuel cost (LUFC) of electricity generation for a fast reactor in a two-component nuclear energy system (NES) with regard for plutonium production. The approach is based on taking into account the additional economic effect, which can be achieved through the sale at the market price of the natural uranium released due to the substitution of thermal reactors by fast reactors with MOX fuel based on the plutonium bred in a fast reactor. This requires considering simultaneously the reactor parts of the fuel cycle for fast and thermal reactors. Relationships have been obtained which connect the key neutronic and fuel characteristics with the NPP and fuel cycle economic performance. The described methodology was used for the computational study of the LUFC for a fast sodium-cooled reactor. Calculations have shown that, in the considered case, taking into account the plutonium production leads to the LUFC reduction by nearly half and, therefore, to a major decrease in the total unit cost of electricity generation (levelized cost of electricity or LCOE).
To address the growing demand for isotopes, it is planned to use irradiation devices in high-power fast sodium reactors. With the help of this type of irradiation devices, mass production of the necessary isotopes is assumed. The designs of irradiation devices for operating time of cobalt-60 isotope in BN reactors are presented. A new version of the irradiation device for use in a high-power sodium fast reactor is proposed. The comparison of different variants of irradiation devices according to the obtained specific activity is given. The new design of the irradiation device combines the retarder units and the steel protection developed for the BN-600 in a single assembly. It allows to achieve cobalt activity of 150 Ci/g for a campaign of fuel (5 years). The results of a study of the azimuthal and radial distribution of the cobalt-60 formation speed to ensure the effective production of the product in a high-power reactor are presented. According to the results of the azimuthal distribution of the neutron capture rate, there is an uneven propagation in the horizontal section of the irradiation device. The maximum capture rate is shifted to the periphery of the irradiation device facing the center of the core. The obtained spatial distribution of the capture rate indicates the possibility of further work to create a more efficient design of the irradiation device for the conditions of a large fast reactor.
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