NPP Unit Research Articles

The rolling simulation for cold work metal hardening

This article describes the results of a calculation and experimental analysis of destructive physical phenomena that appear in critical sections of industrial and power-related equipment, and lead to occurrence of various operational damages. It was shown that pipeline welded connections are the sections most prone to crack development, therefore the traditional strength calculations need to be combined with fracture mechanics criteria and thorough materials analysis of flawing and structural imperfection. The cold work hardening technique was proposed as a solution for the problem of critical sections performance property restoration. The technique uses surface plastic deformation phenomenon to change the material’s throughthickness stress distribution. In order to optimise surface hardening for welded connections prone to defect formation, we proposed a simulation for analysing an actual pipeline sections load. To assess the applicability of the simulation results, the cold work hardening technique was developed and introduced using a full-scale test sample for damaged areas of welded connections in ø426×40 vent pipes at Novovoronezh NPP Unit No.5.

Use of a convolutional neural network to segment signals of motor operated valves

Motor operated valves (MOV) are one of the most numerous classes of the nuclear power plant components. An important issue concerned with the MOV diagnostics is the lack of in-process (online) automated control for the MOV technical condition during full power operation of the NPP unit. In this regard, a vital task is that of the MOV diagnostics based on the signals of the current and voltage consumed during MOV ‘opening’ and ‘closing’ operations. The current and voltage signals represent time series measured at regular intervals. The current (and voltage) signals can be received online and contain all necessary information for the online diagnostics of the MOV status. Essentially, the approach allows active power signals to be calculated from the current and voltage signals, and characteristics (‘diagnostic signs’) to be extracted from particular portions (segments) of the active power signals using the values of which MOVs can be diagnosed. The paper deals with the problem of automating the segmentation of active power signals. To accomplish this, an algorithm has been developed based on using a convolutional neural network.

Determination of the electrical power increase at the generator terminals of a nuclear power plant unit at different condenser states

It is shown that the technical condition of condensing devices of steam turbines largely determines the amount of electricity losses, reliable and economical operation of NPP units. Analysis of the heat transfer process in the condenser showed that the main causes of load reduction are determined by rising cooling water temperature and deviation of steam pressure from normal value. It is shown that among diagnostic parameters except leakage volumes there must be an assessment of contamination of the heat transfer surface which significantly affects the reduction of electricity generation. The modernization main points of the condenser of the Zaporizhzhya NPP power unit No. 3 on the principle of "block-modular" design developed by PJSC "Turboatom" and the characteristics of the condenser provided by the new design are considered. To reflect the real mode of operation of the condensing unit, it is proposed to model the contamination of the heat exchange surface and the presence of leakages in the condenser space using the method of thermal calculation of the condenser by iterative methods. It was found that reducing the increase in electricity generation as a result of the effects of the study factors can partially or even completely absorb the effect of upgrading the condenser plant. It will provide a significant increase in electricity generation with relatively low capital investment compared to construction of new NPP power units and improve the accuracy of power generation forecasts.

The usage of probabilistic assessment for cost calculations of using NPP with hydrogen industrial production

THE PURPOSE. This study focused on the probability of construction of dual – purpose nuclear-hydrogen unit for cogeneration of hydrogen and electricity with nuclear power reactor VVER-1200 based on AES-2006 project. METHODS. The aim of the study is the probation of the IAEA calculation method originated for sea water desalination unit using nuclear power plant as an energy source, but with a view to same time production of high-quality hydrogen and electricity concerning the ecological issues of hydrogen generation. In particular, the method was used for probabilistic assessment of single-purpose NPP unit and dual-purpose nuclear-hydrogen unit. The supposed result of the study was construction of special building for the electrolytic process purposes. The ground location of the building was out of the main building area. The special building should consist of electrolytic units, technological water feed and removal pipelines, tanks for hydrogen and other service equipment. RESULTS. The paper introduced the theoretical possibility of hydrogen production on the rate up to 1,927∙108 m3/year in the case of full-time basis operation of 50 hydrogen units. The rate of produced hydrogen corresponds to 18,53% of inner Russian market hydrogen needs. In this case the electricity cost factor was 0,097 $/kW∙hr, the cost factor of higher quality hydrogen was 0,956 $/m3. The paper introduced the prime cost comparison of produced hydrogen according to hydrogen units total capacity and arrangement demands. CONCLUSION. This method has the limits of applicability, but in our case, it can be used to calculate key economic factors of the project and to analyze the validation of the energy source and the hydrogen unit size.

ЕКСПЛУАТАЦІЙНА НАДІЙНІСТЬ ГЕНЕРУЮЧОГО ОБЛАДНАННЯ ЕНЕРГОБЛОКІВ АТОМНИХ ЕЛЕКТРОСТАНЦІЙ УКРАЇНИ

Statistic data analysis of effective operation of power units of Ukraine NPP has been performed. It has been determined part of unscheduled downtime of power units which occurs due to failures of turbine generators. It was considered indicators of reliability of three types of turbine generators which are used as part of power units of Ukrainian NPPs. Based on analysis of results it was found that in 2015-2019 the average reliability indicators of 1000 MW turbine generators, both two-pole and four-pole, do not fit the requirements of the current standards. The main types of damage are mentioned. The most dangerous between them is depressurization of the stator winding rods, the appearance of cracks in the intercoil bridges of the rotor winding, and hydrogen leakage in gas coolers. Possible reasons for malfunctions in the operation of elements and construction units and shortcomings of the systems control of the technical condition of machines were analyzed. It was proposed effective measures to improve the operational reliability of equipment. In particular, it is mentioned the necessity of introducing automated systems for continuous monitoring of hydrogen moisture in the turbine generator. References 6, table 3.

A conceptual methodology for site exclusion boundary and site large early release frequency for multi-unit nuclear power plants site

Probabilistic Safety Assessment (PSA) risk metrics Core Damage Frequency (CDF) and Large Early Release Frequency (LERF) are currently applied for single NPP unit. The purpose of the work is to arrive at quantitative value for LERF for a site consisting of many NPPs. For this objective, the work proposes to define an exclusion boundary for the whole site (site exclusion boundary) which is different from exclusion boundary for one NPP. At a site, the exclusion boundaries of the individual NPPs may overlap or can be separate. In the present research, various concepts of total exclusion boundary length for the site are delineated upon using the exclusion radius/boundary of individual NPPs. A case study for a hypothetical site consisting of three NPP units was considered for the demonstration of the proposed methodology. The NPPs have same power level and equal radius of exclusion boundary. LERF results are available for individual NPPs and those accident sequences are relevant that (initiating events are independent events or common cause events) that cause release of more than 4% of core I-131 radioactive nuclide within 10 h of accident. The radionuclide dispersion was calculated using Gaussian plume model for dose at various locations on the site exclusion boundary for the multiple NPP site. The calculation of site LERF was carried out for various locations on the site exclusion boundary for a specific configuration of NPPs at site.

Stress Strain State of Steam Turbine Components under Plastic Deformation

Reliable operation of secondary equipment of PWR nuclear power plants is an integral part of nuclear and radiation safety of the entire NPP unit. The problem of stress strain state of steam turbine structural components under plastic deformation is considered. The theory of elastic-plastic deformations is used to solve the problem along with the finite element method. The paper presents the results of computer assessment of stress strain state of locking joint of working blades of the first stage of a intermediate-pressure cylinder (IPC) and high-pressure cylinder (HPC) body of a steam turbine, which makes it possible to characterize the degree of relaxation and stress redistribution in the structure in comparison with obtained earlier results. It is provided that the use of the presented calculation method in designing new structures of steam turbine components operating in the area of high thermal and power loads, taking into account the contact interaction of components, as well as different mechanical and physical properties of materials, and their changes depending on operating temperature, at this stage of software development allows one to identify problem areas in the design and prevent further breakdowns in the turbine. Based on the comparison of operational data of the developed design solutions and calculation assessment, it is proved that the chosen calculation method can significantly increase the operational reliability not only of the turbine unit but also the nuclear unit as a whole, as well as reduce economic costs caused by turbine unit downtime during maintenance.

Investigation of irradiated metal of WWER-type reactor internals after 45 years of operation. Part 3. Microstructure and phase composition

TEM, SEM, and APT techniques have been used to analyze radiation-induced components of metal structure of fragments cut from the pressure vessel internals of Novovoronezh NPP Unit No 3 after 45 years of operation. The fragments differed in the neutron damaging doses (from 14 to 43 dpa) and the irradiation temperature (from 285 to 315°C). The density and dimensions of titanium carbides and carbonitrides, dislocation loops, radiation-induced voids, segregations, and nanoscale precipitates were determined. The contributions of structural components to the radiation hardening of the investigated fragments of 18Cr-10Ni-Ti stainless steel were estimated.

Investigation of irradiated metal of WWER-type reactor internals after 45 years of operation. Part 1. Research program and cutting out of samples from pressure vessel internals

The program is presented for investigations of the metal of the most irradiated elements of the WWER-440 reactor of the Novovoronezh NPP Unit 3 decommissioned after 45 years of operation. The fragments (cylindrical samples) were cut out from various zones of the core baffle and segment of forming ring of core barrel.

Investigation of irradiated metal of WWER-type reactor internals after 45 years of operation. Part 2. Calculated and experimental determination of the fast neutron fluence and damage dose

Fast neutron flux, fluence and damage dose have been determined when using experimentally measured specific activity of 54 Mn и 58 Co isotopes for metal of samples cut out from elements of pressure vessel internals of Novovoronezh NPP Unit No 3 (18Cr-10Ni-Ti steel, analog of AISI 321 steel). The results have been compared with the values calculated by KATRIN-2.5 computer code.

Providing rationale for the possibility of decommissioning Bilibino nuclear cogeneration plant based on the onsite disposal option

The problem of the NPP decommissioning after the end of the specified or extended life has reached the practical solution stage for countries possessing a nuclear power industry. The major decommissioning options, both in Russia and abroad, include immediate dismantling and deferred dismantling. At the same time, there are NPP units for which, for a number of reasons, none of the two options are acceptable in terms of ensuring the safety of the personnel, the public and the environment. Disposal, the third and a more rare option, shall be used for decommissioning in this case. The purpose of the work is to provide rationale for the possibility of decommissioning Bilibino Nuclear Cogeneration Plant based on the Onsite Disposal option by covering the main building with an inert material with the formation of a mound. The option has been selected considering the results of an integrated analysis taking into account the geographical, operational, radiological, and socioeconomic factors, as well as based on a limited experience of decommissioning commercial uranium-graphite reactors both within and outside Russia. In accordance with Russian law, the decommissioning stage will start after spent nuclear fuel is withdrawn from the unit and removed. Emphasis is placed on the proposed option preparation and implementation issues. Dates and sequences for the performance of operations to dismantle the components and civil works of buildings and structures, as well as the onsite protective mound formation structure and composition are discussed. The geometrical dimensions, as well as the quantities and types of the mound-forming materials have been estimated. The key mound-forming materials will be fragments of the components, the biological shielding, and the civil works, as well as local materials.

Geology, Tectonics and Stratigraphy of the Construction Site of the New Bushehr NPP Units in the Islamic Republic of Iran as Part of Recent Geotechnical Studies

Southern Iran in the area of Zagros and the borders of the Arabian and Eurasian plates is a seismically active territory in which large industrial facilities are located, including Bushehr NPP. In this regard the relevance of studying modern geodynamics and geology of the region is understandable. The geological structure of the territory after engineering surveys of 1974-2001 no longer seemed questionable. However, after completion of engineering surveys for new NPP units in 2015, new views on some positions on seismotectonics, and later on the geology of the area, appeared. The article provides information about the geology, tectonics and stratigraphy of the region and the research area, including not covered earlier in domestic reporting materials and scientific articles, and also considered the possible reasons for the appearance of other interpretations regarding seismotectonics and geology of the area where the NPP site is located. A brief analysis of the research results, both previously completed and completed relatively recently, is presented. An additional argument is considered in favor of the presence of fault zones within the Bushehr anticline proposed by Iranian researchers. In particular, the Khark-Mish fault supposed by them may be part of the buried ancient anticlinal fold before the position of its axis changes in the modern period as a result of neotectonic processes common to the region as a whole. The geology and tectonics of the Bushehr anticline are compared with similar structures on Fr. Hark and the nearest islands. Updated information on the stratigraphy of individual geological formations of the region and the research area is also provided. In spite of the reasoned justification of various positions on the geology and tectonics of the region, it seems necessary to conduct a number of additional special direct and indirect studies aimed at ensuring the safety of the Bushehr NPPs under construction and operating.

РАСЧЕТНОЕ МОДЕЛИРОВАНИЕ ДОЖИГАНИЯ ТВС ЭНЕРГОБЛОКОВ № 1 И № 2 ЛЕНИНГРАДСКОЙ АЭС ПОСЛЕ ВЫВОДА ИЗ ЭКСПЛУАТАЦИИ

The RBMK-1000 reactor operates in a continuous refueling mode. The reactor core comprises FAs across the burn-up spectrum, from fresh fuel assemblies to the most burnt-up ones. Following the reactor shutdown for decommissioning, the majority of irradiated fuel assemblies (IFA) have the potential for further use (the so-called afterburning) at operating NPP units. Most of the irradiated fuel assemblies have a burn-up fraction, which is far from the specified threshold value. The neutron multiplication factor in the cell exceeds the core average value and, therefore, the IFA loading makes it possible to increase the reactivity margin to the desired value. Reuse of spent fuel assemblies in reactors at other power units offers a number of advantages. In economic terms, afterburning is able to reduce the use of fresh fuel assemblies (FFA). In terms of radioactive waste handling, afterburning is able to reduce the number of irradiated fuel assemblies, which require long-time storage in a spent nuclear fuel repository thus reducing the IFA and radioactive waste disposal loads. JSC NIKIET has proposed the use of irradiated fuel assemblies from units 1 and 2 of Leningrad NPP shut down after decommissioning in reactors at units 3 and 4 of the same NPP.

Integral Logistics in NPP Unit Decommissioning Project

The paper considers the integral logistics of the dismantling work stage during the decommissioning of NPP units and the feasibility of its presentation in the corresponding project. The features of the logistic approach to the organization of dismantling works and subsequent operations of handling dismantled products are shown.

Fluid level sensors with metrological self-check function based on the concentration effect

This paper presents the results of the experiments on studying the properties of concentration elements, which were carried out in order to develop a new principle for measuring the level of conductive and non-conductive polar liquids, as applied to the operating conditions of nuclear and thermal power facilities. The paper includes the methods for increasing the level and stability of the useful signal of concentration elements and design solutions for creating the fluid level multi-electrode sensor.Considering the current trends towards an increase in the number of measuring channels at NPP and TPP power units and the need to optimize metrological service, it is noteworthy that the concentration effect is considered not only in terms of a new principle for measuring the liquid level, but also implementation of metrological self-check of conductometric and capacitive fluid level sensors.

Comparison of the high Ni VVER-1000 weld microstructure under the primary irradiation and re-irradiation

This paper presents the first comparative experimental assessment of the microstructures of the same surveillance specimens of VVER-1000 high Ni weld: after the primary irradiation, recovery annealing and re-irradiation in the same industrial NPP (Balakovo NPP unit 1) to assess the possibility of its lifetime extension after annealing up to 60 years. Therein, studies of both the initial (carbides) and radiation-induced hardening phases (precipitates and dislocation loops), and the behavior of grain boundary segregation as well are presented.It has been shown that the microstructures of high Ni VVER-1000 weld after the primary irradiation and re-irradiation after recovery annealing up to the close values of fast neutron fluences are identical: the characteristics of both initial and radiation-induced hardening phases, as well as grain boundary segregation, are the same.

Optimization and Improvement of Electric Drive Valve Diagnostics Process During Pre-Commissioning Activities at NPP Units Under Construction

The article discusses the need for technical diagnostics of electric drive stop valves, and there are presented applied methods for evaluating the technical condition. In addition, an approach to the organization of commissioning works related to the configuration of electric drive valves is revealed, based on their combination with diagnostic support, which allows to improve the quality and efficiency of autonomous and complex commissioning as well as to increase the effectiveness of technical management of hydraulic tests and reduce their duration.

Assessment of the personnel reliability indicators during long-term operation of a nuclear power plant unit

The purpose of the work is to form and discuss the key components of the methodology to obtain the quantitative indicators of the personnel reliability based on the actual long-term operation experience data for a particular power unit. The timeliness of this work and similar studies is based on a simple judgment that the personnel reliability performance at similar units, in the best case, and in associated industries, in the worst case, that is, the reliability of personnel at other industrial facilities, is used to justify the design when designing power plant units. Accordingly, the obtained safety assessments with respect to personnel have nothing to do with the facility the safety of which is justified. This requires respective methods and procedures to update the safety criteria with regard for the actual operation experience, as a minimum, based on the actual reliability of the NPP unit personnel. The key components are presented for shaping the methodology to obtain the quantitative indicators of the personnel reliability based on data of the unit’s long-term actual operation experience. Recommendations and explanations are provided for each of the methodology’s key components, namely: an information model of the methodology, the key indicators and other components are provided. The timeliness of the methodology development is explained making it possible to obtain quantitative indicators based on the nuclear plant unit’s operation experience. An additional methodology is presented to assess the safety of nuclear power plants. A unique notional definition of the nuclear plant personnel reliability, and the procedures to justify the power unit safeguards with regard for the human factor aspects have been proposed. An information model of the methodology is provided and the prospects of its application to improve the safety justification procedure for various components of the nuclear plant units are described. To conclude with, ways are presented for the further evolution of the proposed methodology, and the scope of the methodology and the expected positive effect from its application are described.

Ukrainian NPP Seismic Resistance Assessment Using Provisions of Regulatory Guideline NP 306.2.208-2016

Since November 2016, the new Regulatory Guideline NP 306.2.208-2016 “Requirements for Seismic Resistance Design and for Evaluation of Seismic Safety of Ukrainian NPPs” [1] has been in force in Ukraine. This Guideline was developed to improve requirements for NPP site seismic hazard assessment, NPP seismic resistance design and assessment/review of Ukrainian NPP seismic safety.
 Energoatom developed the Organizational and Technical Measures for Implementation of NP 306.2.208-2016 [2] approved by State Nuclear Regulatory Inspectorate of Ukraine to perform NP 306.2.208-2016 [1] requirements.
 The paper considers the status of Energoatom in implementation of the main organizational and technical measures [2] on increasing seismic resistance of Ukrainian NPP units according to NP 306.2.208-2016 [1]. In particular, these measures are the following: specification of NPP site seismicity considering results of new studies; introduction of changes into classification (seismic categorization) of systems and components; analysis of necessity to consider additional load combinations with seismic loads, specification of assessing seismic resistance of structures, systems and components; seismic probabilistic safety assessment of NPP units.

Results of Analysis of Aging Related Events at Ukrainian NPPs

The design lifetime (30 years) of Ukrainian NPPs has already been expired or will be expired soon. One of the priority areas for the development of nuclear energy is long-term operation (LTO) based on the results of periodic safety review. At present, eleven Ukrainian NPP units are operated under LTO conditions, which in turn causes certain features of operation related to wear, fatigue and general aging of components and structures.
 An issue of aging management is considered one of the main factors to ensure the safety of a nuclear installation, both in the design lifetime and in the long-term operation. The primary purpose of aging management is to ensure the safety and maximum efficiency of operation through the implementation of technically and economically feasible measures aimed at timely detection and keeping of degradation of NPP components caused by aging within the limits.
 One way to determine the efficiency of implemented measures and aging management programs is to analyze operational experience and, in particular, analyze the number of NPP operational occurrences during the design and long-term operation period and that are directly related to the aging effects. This paper presents the results of the analysis of the events at Ukrainian NPPs caused by aging processes, compares the results of national and international experience.