Features of methods for monitoring the fuel cladding tightness in lead-cooled fast breeder reactors

To timely detect failed fuel elements, a reactor plant should be equipped with a fuel cladding tightness monitoring system (FCTMS). In reactors using a heavy liquid-metal coolant (HLMC), the most efficient way to monitor the fuel cladding tightness is by detecting gaseous fission products (GFP). The article describes the basic principles of constructing a FCTMS in liquid-metal-cooled reactors based on the detection of fission products and delayed neutrons. It is noted that in a reactor plant using a HLMC the fuel cladding tightness is the most efficiently monitored by detecting GFPs. The authors analyze various aspects of the behavior of fission products in a liquid-metal-cooled reactor, such as the movement of GFPs in dissolved and bubble form along the circuit, the sorption of volatile FPs in the lead coolant (LC) and on the surfaces of structural elements, degassing of the GFPs dissolved in the LC, and filtration of cover gas from aerosol particles of different nature. In addition, a general description is given of the conditions for the transfer of GFPs in a LC environment of the reactor being developed. Finally, a mathematical model is presented that makes it possible to determine the calculated activity of reference radionuclides in each reactor unit at any time after the fuel element tightness failure. Based on this model, methods for monitoring the fuel cladding tightness by the gas activity in the gas volumes of the reactor plant will be proposed.

Dynamic statistical assessment of the competitiveness of an energy generating company (as exemplified by Rosenergoatom Concern JSC)

The depletion of traditional organic energy sources and aggravated environmental problems are the reasons why the level of energy efficiency is an important factor in the competitiveness of the national economy. Russia ranks third in the world in terms of total energy consumption and its economy is distinguished by a high level of energy intensity (amount of energy per unit of GDP). In 2019, this figure was 9.62 tons of oil equivalent (toe) per 1 million rubles, which is 40% higher than the world average. The low energy efficiency of the Russian economy is a widely recognized problem. A special decree of the Government of Russia in 2018 sets the task of increasing the level of energy efficiency of the Russian economy by 23% by 2030. One of the ways to solve this problem is the development of nuclear energy, and increasing the competitiveness of nuclear energy is one of the key issues for the national economy. In this connection, solving the problem of assessing the competitiveness of the nuclear industry and its leading companies occupies a key place among the practical scientific problems, the solution of which is facilitated by the results presented by the authors in this article. Rosenergoatom Concern JSC is the leading energy generating company in the Russian nuclear industry. The results of the study of the competitiveness of Rosenergoatom Concern JSC were obtained on the basis of the authors’ methodology for assessing the competitiveness of an energy generating company. The novelty of the presented methodology lies in the developed normative and evaluative model and the coefficients of competitiveness of an energy generating company. The advantages of the authors’ model are that it allows (1) obtaining integral assessments of the competitiveness of a power generating company at short time intervals for a large number of indicators and (2) quantitatively measuring the effects of different factors on the competitiveness of a power generating company, provided that the grouping of indicators of competitiveness of a power generating company is justified by influencing factors. The two factors considered by the authors were: the general market factor and the industry factor. According to the results of the study, it was found that Rosenergoatom Concern JSC demonstrates positive increase of the competitiveness indicator mainly due to the industry factor. With this regard, it was concluded that, within the framework of state policy, it is advisable to strengthen support for the Russian nuclear industry by creating additional conditions and opportunities for its energy generating companies on the domestic energy market.

Analysis of numerical studies on the thermal-hydraulic and neutronic thermal-hydraulic stability of supercritical water reactors

The paper presents a review of modern studies on the potential types of coolant flow instabilities in the supercritical water reactor core. These instabilities have a negative impact on the operational safety of nuclear power plants. Despite the impressive number of computational works devoted to this topic, there still remain unresolved problems. The main disadvantages of the models are associated with the use of one simulated channel instead of a system of two or more parallel channels, the lack consideration for neutronic feedbacks, and the problem of choosing the design ratios for the heat transfer coefficient and hydraulic resistance coefficient under conditions of supercritical water flow. For this reason, it was decided to conduct an analysis that will make it possible to highlight the indicated problems and, on their basis, to formulate general requirements for a model of a nuclear reactor with a light-water supercritical pressure coolant. Consideration is also given to the features of the coolant flow stability in the supercritical water reactor core. In conclusion, the authors note the importance of further computational work using complex models of neutronic thermal-hydraulic stability built on the basis of modern achievements in the field of neutron physics and thermal physics.

Possibility of simulating natural circulation in fast neutron reactors using a light water test facility

The paper evaluates the possibility of modeling the heat transfer phenomena in a liquid-metal coolant using a light water test facility. It considers the natural circulation of the coolant in the upper plenum of the fast-neutron reactor. The sodium-cooled BN-1200 reactor was selected as the reactor installation to be modeled. The development of novel reactor designs must be based on the results of experimental studies. Some problems of modeling thermohydraulic processes in BN type reactors are studied by using sodium test facilities. Experimental studies of natural convection processes using light water test facilities can be considered as a good alternative to those using sodium test facilities. To validate the model, the similarity theory and the “black box” method were used and their principles and applicability were analyzed. Using the “black box” method makes it possible to avoid detailed modeling of such components as the reactor core and heat exchangers, replacing them by a simplified representation of these components to simulate the integral characteristics of the existing real life equipment. The paper considers the basic criteria which determine the similarity of the thermohydraulic processes under study. The governing criteria of similarity were estimated based on the fundamental differential equations of natural convection heat transfer. Based on these criteria, a set of dimensionless values was obtained which show the correlation between the model parameters and the characteristics of the reactor facility. Besides, generalized relationships were derived which can be used to estimate the scaling factors for calculating the key values of the reactor facility based on the model parameters. These relationships depend on the thermal-physics parameters of the working fluids, the geometrical scale value and the ratio of the thermal power of the model to that of the reactor facility, i.e., model-to-reactor thermal power ratio. The conditions under which it is possible to model sodium coolant by light water with adequate accuracy were analyzed. An example is given of the numerical values of the scaling factors for one of the reference light water test facilities. The paper uses the experience of a number of foreign researchers in this field, in particular, the accepted assumptions which do not result in serious loss in modeling accuracy. According to the available estimates, the assumptions used do not result in considerable losses in accuracy. Thus, the natural circulation of the sodium coolant in the upper plenum of the fast-neutron reactor can be simulated with adequate accuracy by using light water test facilities.

An expert neural system for diagnostics of motor-driven valves

Trouble-free operation of motor-driven valves (MDV) is one of the key factors behind the operating safety of NPPs. As critical components, MDVs are a part of a safety system and a safety-related system. This imposes the highest possible requirements on the MDV reliability. MDVs are the most numerous category of the NPP components. Depending on design, one power unit contains 1500 to 3000 motor-driven valves alone. It follows from an analysis of the NPP failures that many of these are caused by failed motor-driven valves of safety and safety-related systems. The paper presents a description of an automated system for diagnostics of shutoff and control MDVs used in the NPP pipelines. The developed diagnostic algorithms make it possible to take into account the variability of the MDV technical parameters, while taking into account, at the same time, rated restrictions on diagnostic parameters, if any.

Methodology for calculating the criteria of economic efficiency of investments in nuclear icebreakers

An economic and analytical model for evaluating the criteria of efficiency (profitability) of investments in the projects of innovative nuclear icebreakers of the Northern Sea Route is suggested. The model is based on the new analytical representation of the methodology for forecasting the investment project efficiency that is widely used in international practice. The mathematical expression for the net discounted income provides convenient formulas for calculating several investment efficiency criteria for nuclear icebreakers: internal rate of return, minimum annual revenues from icebreaker convoys, discounted payback period, and the volume of delivered cargo. The paper gives estimates of the criteria for the efficiency of investments in “Leader” class icebreakers that depend on the discount rate of cash flows, capital, and operating costs. It is shown that at high capital costs, typical for construction of “Leader” class nuclear icebreakers, the minimum required revenue of an icebreaker, representing a financial burden for ships transporting cargo along the NSR, rapidly increases with the growth of discount rate and the reduction of investment payback period. This means that the profitability of such icebreakers is only possible at low discount rates of 2–3% per year, which is an extremely low-interest credit. Even with low interest and impressive technical characteristics of the icebreaker (high speed of navigation, large number of ships in the caravan and their maximum capacity) the payback period would exceed 25 years.

Studies of critical heat fluxes in small diameter channels

The paper presents the results of experimental studies of critical heat flows in vertical small diameter channels, when the coolant moves from bottom to top, which were carried out in the Obninsk branch of MEPhI in the 1970s of the last century but have not become widespread due to the lack of demand for their practical use. Nowadays, the interest in such works is manifested, first of all, in the development of compact plants and devices, particularly in nuclear power engineering. As a coolant, water, Freon-12 and 96% ethyl alcohol were used. High velocities of underheated liquid at high heat fluxes on the channel wall lead to the so-called “fast crisis” of heat transfer. In this case, the magnitude of the heat flux depends mainly on the parameters of the coolant flow in the wall zone rather than the flow core. The “slow crisis” is mainly observed at high vapor concentrations, relatively low mass flow rates and in an annular-dispersed flow. The value of the critical heat flow in this case depends mainly on the flow parameters in the core, which are probably close to the average coolant flow parameters. The conditions in the near-wall region are also largely determined by the flow in the core. High heat transfer coefficients in a flow moving at high speed usually result in a much smaller and slower rise in the wall temperature. Sometimes a DNB heat flux can occur bypassing the boiling process. In the core of a VVER-type reactor operating in its nominal mode, surface boiling is present in a number of fuel rods. Probably, surface boiling will also be present in transportable and small-size nuclear power plants. Therefore, an important task is to conduct relevant research in this area.

System levelized fuel cost of electricity generation in a two-component nuclear energy system with a closed uranium-plutonium NFC

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).

Synergetic effects of the combined action of carbon ions and the chemotherapy drug doxorubicin on HeLa cancer cells

Proton and carbon beam therapy is currently recognized as the most effective and highly accurate form of radiation therapy for deeply located tumors, including radioresistant ones. This is due to the fact that they have all the advantages of spatial dose distribution and, at the same time, are densely ionizing radiations capable of effectively affecting hypoxic, slow-growing tumors and other neoplasms that are insensitive to traditional types of radiation. It is well known that one of the main methods for treating neoplasms is chemotherapy. The predominant mechanism of action of anti-tumor drugs is the induction of DNA damage with the subsequent impossibility of repair. In our study, we used an anti-tumor antibiotic of the anthracycline series, doxorubicin. The assessment of the potential significance of the synergistic interaction of ionizing radiation with chemical preparations in medical radiology remains an urgent and unresolved problem. It is possible to achieve the maximum effect of the combined action of two agents when they act simultaneously. The phenomenon of synergy can be used to optimize the combined use of radiation and chemotherapy in clinical practice. In this regard, it seems relevant to conduct a study for HeLa cancer cells exposed to ionizing radiation, an antitumor drug, as well as their combination. In the course of the study, results were obtained on the manifestation of the synergistic nature of the agents used, which is of great practical and theoretical importance for understanding the mechanism of the combined effect of ionizing radiation and the chemotherapy drug (doxorubicin). The obtained data can be helpful in optimizing the combined effects in order to achieve maximum synergistic interaction.

Increasing the production of the Mo-99 isotope by modernizing the design of targets irradiated in the experimental channels of the VVR-c reactor

There are various ways to obtain Mo-99. Some of them are widely used in industrial production, others are in the research stage with the aim of increasing the product yield. The main industrial method for obtaining Mo-99 using a nuclear reactor is the fragmentation method. This method provides for the presence of a uranium target and a nuclear reactor. The target is placed in the channel of the reactor core and irradiated with neutrons for the required time. After that, the target is removed from the channel to the “hot” chamber for the chemical separation of Mo-99. This is how Mo-99 is obtained practically all over the world. The paper considers the fragmentation method for producing Mo-99, which is implemented on the basis of the engineering and technological complex of the VVR-c research nuclear reactor. In order to increase the yield of Mo-99, a modernized model of the “tube-in-tube” target is proposed. The assessment of the production of Mo-99 and the cooling efficiency of the modernized target was carried out. The calculations were performed using the VisualBurnOut and Ansys CFX software packages. Computational studies have shown an increase in the energy release and the amount of the produced Mo-99 isotope in the target of the modernized design. In the most stressed zones, the target wall temperature exceeds the water saturation temperature. Surface boiling occurs in these zones. As a result, turbulization and mixing of the near-wall boundary water layer increases. This improves heat dissipation.