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Spectral regulation is based on hardening the neutron spectrum at the start of a reactor run to attain the greatest accumulation of plutonium followed by softening of the spectrum toward the end of the run. There are different methods for performing such regulation -ranging from changing the coolant density during operation to changing the water-uranium ratio in the fuel assemblies.This paper presents the results of computational studies using an estimated value of the increase in VVÉR-1000 fuel burnup using zirconium displacers, placed in some of the guiding channels of the safety and control system rods. At the first stage of reactor operation, the zirconium displacers are inside the guiding channels; at the second stage, after the boric acid concentration reaches zero concentration, they are successively extracted from the core without cooling down the reactor, the excess reactivity formed maintains the reactor in a critical state without adding boric acid to the coolant.Such an arrangement of the displacers is impossible for VVÉR-1000 with 61 control rod drives because the required number of absorbing rods is found under them and there are no additional drives for extracting the zirconium displacers without cooling down the reactor. This makes such a method of spectral regulation impossible.The modern design of a VVÉR-1000 reactor (V-392) has 121 control rod drives. For them, it is possible to search for variants for replacing a certain number by zirconium displacers and implementing spectral regulation.The investigations were performed using the CONSUL program system [1, 2] which was designed to calculate the characteristics of light-water nuclear reactors based on mutually consistent calculations of neutron, temperature, and isotopic fields. The calculations were performed for a stationary fuel cycle with a 4-yr run. The average enrichment of the fresh fuel was 4.12%; six fuel elements, containing a homogeneous mixture of uranium-gadolinium fuel, were placed in each fuel assembly. The arrangement of the core was realized for a stationary regime of reloadings with low neutron leakage -the fuel assemblies used in the final year of operation are placed along the periphery of the core.As one can see in Fig. 1, the total number of control rods is 61 and the number of fuel assemblies with zirconium displacers in the guiding channels is 60.The characteristics of a stationary fuel load with regulation of the neutron spectrum were compared with the characteristics of a load without zirconium displacers (the guiding channels of the control rods in this variant were filled with water).A reactor with completely inserted zirconium displacers reaches zero critical boric acid concentration at 269 eff. days (Fig. 2). Then successive extraction of zirconium displacers from the fuel assembly starts (Table 1). The stationary load operates in this regime for 298.1 eff. days as compared with 294 eff. days without regulation of the spectrum ( Table 2).The plutonium mass in the core with spectrum regulation is greater by 10 kg th...

CONSUL code package designed for the calculation of reactor core characteristics has been developed at the beginning of 90-th. The calculation of nuclear reactor core characteristics is carried out on the basis of correlated neutron, isotope and temperature distributions. The code package has been generally used for LWR core characteristics calculations. At present CONSUL code package was adapted to calculate liquid metal fast reactors (LMFR). The comparisons with IAEA computational test “Evaluation of benchmark calculations on a fast power reactor core with near zero sodium void effect” and BN-1800 testing calculations are presented in the paper. The IAEA benchmark core is based on the innovative core concept with sodium plenum above the core BN-800. BN-1800 core is the next development step which is foreseen for the Russian fast reactor concept. The comparison of the operational parameters has shown good agreement and confirms the possibility of CONSUL code package application for LMFR core calculations.

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Abstract. This paper shows basic features of different fuel assembly (FA) application for VVER-1000 in a closed fuel cycle based on REMIX-technology. This investigation shows how the change in the water-fuel ratio in the VVER FA affects on the fuel characteristics produced by REMIX technology during multiple recycling.