Vol 124, No 1 (2018)

An emergency heat removal system (SAOT) that removes heat from the secondary loop of a fast sodium reactor by air cooling the surfaces of the piping and equipment of the heat-sink loops of the secondary loop is described and ways to optimize it are indicated. A method of evaluating the efficiency of such an SAOT is described, and the results of an evaluation for a fast sodium reactor are presented as an example showing that the system can be used in fast sodium reactors of any power capacity.

A methodological approach and the basic tenets for evaluating the reliability of in-reactor monitoring of VVER are presented. The method is based on the statistical analysis of indications in real time and includes methods for evaluating the admissible maximum error of the measurement channels used for monitoring as well as the average value and admissible deviation of indications in groups of parallel monitoring channels, as well as a method of evaluating reliability by comparing the values of a parameter with the regime values. In comparing the indications of a monitoring channel with the indications of other parallel channels, the median value is proposed as the baseline value. The developed method is implemented in the Diagnostika SVRK special software, which has been successfully tested during the commissioning of the No. 1 unit at the Novovoronezh NPP-2.

Mathematical modeling is used to investigate the effect of the thermophysical non-uniformity of the core in a reactor on the behavior of radiation-chemical processes in the first-loop water coolant of pressurizedwater power reactors. The problem of determining the critical hydrogen concentration in coolant that is sufficient to maintain the concentration of oxidizers in the coolant at a corrosion safe level is used as an example. It is shown that in a reactor the critical hydrogen concentration may not have a definite value but rather a range of values dependent on the radiation-chemical process and the reactor’s thermo- and neutron-physical parameters. Calculations also showed that the conditions under which oxidizer formation is suppressed can be determined accurately only with detailed three-dimensional modeling of thermophysical phenomena and radiation-chemical transformations in the entire core volume.

The particularities of the axial and azimuthal asymmetry of nodular corrosion of RBMK-1000 fuel-element cladding operating in FA at power 1.7–2.2 MW are examined. The measured thickness of the oxides is compared with the concentration of the oxidative products of radiolysis in the coolant and the computed distribution of the thermophysical parameters in a fuel channel of the reactor. It is shown that the axial asymmetry of the oxidation of the fuel elements could be due to the temperature distribution in cladding and the non-uniform content of radiolytic oxygen and the radicals HO₂ and \( {\mathrm{O}}_2^{-} \) over height in FA and the azimuthal distribution is due to the radial distribution of the fast and thermal neutron fluxes. The results of studies attesting the possibility of the appearance in the RBMK-1000 fuel channel of conditions where the corrosion rate of the cladding on the sections between the spacer grills is comparable to the oxidation rates of VVER-1000 fuel elements are presented.

The results of radioecological monitoring of agricultural activities within the 30-km impact zone of the Siberian Chemical Combine are examined. The surface activity of ¹³⁷Cs in soil and the specific activity of ¹³⁷Cs in plants with similar indicators characteristic for NPP sites are analyzed and compared. The obtained data make it possible to evaluate the impact of a prototype electric power complex (PEPC) on the soil-and-vegetation cover and the products of agricultural activity, since the data make it possible to differentiate information on two basic parts – that associated with the activity of the Combine, on the one hand, and the other with the possible contribution of PEPC, on the other.