All-Russian Scientific Research Institute for Operation of Nuclear Power Plants

The article presents the results of the analysis and generalization of Russian and foreign experimental programs for the study of combustion modes of hydrogen-containing mixtures as applied to hydrogen issues at nuclear power plants (NPPs) with VVER during severe accidents. An approach to criteria-based estimates of flame acceleration modes and deflagration-to-detonation transition for mixtures containing hydrogen and carbon monoxide is formulated. The effects of water droplets in the gas phase on the flammability and combustion modes of hydrogen mixtures are discussed. The results of this work are relevant for the assessment of hydrogen hazards at NPPs, including the development, validation, and application of dedicated computer codes.

In 2022, a hybrid muon hodoscope with a sensitive area of $$3\times 3$$ m $${}^{2}$$ for studying the internal structure of large-scale objects using the muonography method was created at MEPhI. The hodoscope’s detecting system has a hybrid structure. It consists of a scintillation strip detector and a drift tube detector and is designed to record tracks of charged particles. The muonography method is based on the use of cosmic ray muons as penetrating radiation for ‘‘translucence’’ (analogous to radiography) of large-scale objects. Experimental studies of the internal structure of the Kalinin NPP power unit using the muonography method were carried out in 2022–2023. The paper presents a brief description of the design of a hybrid muon hodoscope, as well as the results of an experiment on diagnostics of the power unit structure using this method, which was carried out during the scheduled power unit’s maintenance. The purpose of the experiment was to develop a method for real-time detection of changes in the structure of a reactor unit during its maintenance.

The results of the numerical simulation of measurements of scram worth during the start-up phase of the second and third fuel loads of the Novovoronezh Nuclear Power Plant unit 6 are presented. The measurements of scram worth for a partially burned-up core are numerically simulated according to the method, which was previously developed at the Scientific and Engineering Center for Nuclear and Radiation Safety and successfully applied to the physical start-up tests of units of nuclear power plants with VVER reactors. A comparison of calculated and measured currents of ionization chambers and reactimeter readings when measuring scram worth at the start-up phase of the second and third fuel loads is presented.

Hydraulic tests are used in various sectors of the national economy to check the strength and tightness of vessels and pipelines, their parts and assembly units loaded with pressure. The hydraulic test pressure is a calculated value and is determined on the basis of regulatory documentation for the relevant control objects. Analysis of current trends in the field of hydraulic testing both in the Russian Federation and abroad has shown a trend to reduce the damageability of test objects by choosing the most optimal hydraulic test pressure. The main purpose of the research was to reduce the operational damage to equipment and pipelines of nuclear power plants by reducing the pressure of hydraulic strength tests during maintenance. The research is based on probability theory, mathematical statistics, strength physics and fracture mechanics, taking into account the possibility of occasional discontinuities or defects that might be observed in operation. The method is based on a risk-based approach, which makes it possible to determine the permissible risk variation based on recommendations on the safety of nuclear power plants in the Russian Federation. The objects of research are the equipment and pipelines of nuclear power plants. The result of the research is the development of a method substantiating the reduction of the pressure of hydraulic strength tests for equipment and pipelines of nuclear power plants based on a risk-based approach. The developed method can be used by organizations involved in the production of electricity (at nuclear or thermal power plants), transportation of oil, gas or other substances, at facilities where pipelines are an essential part of their structures, affecting the reliability and efficiency of operation of these facilities.

This paper presents the concept of a passive electrochemical hydrogen recombiner (PEHR). The reaction energy of the recombination of hydrogen and oxygen is used as a source of electrical energy according to the operating principle for hydrogen fuel cells to establish forced circulation of the hydrogen mixture as an alternative to natural circulation (as is not utilized in conventional passive autocatalytic hydrogen recombiners currently used in nuclear power plants (NPPs)). The proposed concept of applying the physical operation principles of a PEHR based on a fuel cell simultaneously increases both productivity in terms of recombined hydrogen and the concentration threshold of flameless operation (the ‘ignition’ limit). Thus, it is possible to reliably ensure the hydrogen explosion safety of NPPs under all conditions, including beyond-design accidents. An experimental setup was assembled to test a laboratory sample of a membrane electrode assembly (MEA) at various hydrogen concentrations near the catalytic surfaces of the electrodes, and the corresponding current–voltage characteristics were recorded. The simplest MEA based on the Advent P1100W PBI membrane demonstrated stable performance (delivery of electrical power) over a wide range of hydrogen concentrations.

The approaches to the organization of radiation monitoring during normal and abnormal operation are fundamentally different. In the event of a radiation accident, the means and methods for monitoring radiation parameters intended for normal operation are not always applicable. The article discusses approaches to the radiation monitoring strategy implementation aimed at obtaining timely radiation situation information for decision-making of protective measures taking into account the recommendations given in IAEA and ICRP documents.