Corrosion monitoring application in Taiwan's nuclear power plants

Abstract

Corrosion monitoring methods have been applied extensively for system condition diagnosis, material degradation resistance evaluations, and water chemistry optimisation in Taiwan's boiling water and pressurised water reactor nuclear power plants. The online corrosion monitoring systems developed and currently applied in Taiwan are reviewed. Examples of applications discussed include electrochemical potential monitoring, online crack growth rate measurements, electrochemical noise monitoring, linear polarisation resistance monitoring, and potential drop pipe thinning monitoring. Online corrosion monitors have proven useful tools within the nuclear power plant monitoring systems currently installed and have achieved their specific objectives in the context of Taiwan's power plants.     

中低温废热发电的思路与方法

在工业生产过程中,存在着大量具有一定温度品质的热能被放散。实践中,可以通过某种设备系统将其回收利用,既节约了宝贵的一次能源,又改善了环境质量。中低温废热发电就是回收废热而生产二次优质能源的一种方法。     

Green's function solution of temperature field for flow in porous passages

Recently, the heat transfer in porous passages has received attention from many investigators. The Green's function solution method can serve as a powerful tool to accomplish this task of providing solutions to this type of problems with or without the effect of axial conduction. The study of heat transfer with emphasis on frictional heating, in the absence of axial conduction, is the subject of this presentation. As a simple example, consideration is given to the numerical study of the heat transfer in flow between two impermeable parallel plates. The individual effects of temperature change at the walls, frictional heating, and the combined effects are examined. The data shows that the combined effects can produce removable singularities under certain boundary conditions. To avoid the occurrence of singularities in these types of applications, certain heat transfer parameters are presented in different but basic forms.     

Life duration of PWR nuclear power plants

The importance of the Pressurized Water Reactor (PWR) nuclear plants in the whole of the electrical production facilities of EDF is a good reason why a special effort is devoted to assessing their life duration. It seems that the longevity of the PWRs is going to show more favourable technical and economical conditions than did the previous steam generating plants.

The EDF ‘life duration project’ includes a four-year task program. First, a full inventory of the available data will be drawn up in order to forecast the ageing of the sensitive materials of a power plant and to follow up its development so as to anticipate or to remedy problems. These sensitive materials are those for which the difficulties and the cost of restoration would not allow the inclusion of those operations within the normal framework of maintenance programs.

The first analysis of how much these materials may be damaged leads one to believe that the main results of such ageing, which occur mainly in reactor vessels as embrittlement due to exposure and also in the fatigue of the main components of the boilers, will not limit the life of these sensitive materials, except in the very long term.

Overcoming the effects of certain ageing or materials corrosion damage may well give difficult problems to maintenance so that it is vital to forecast and assess them. If this necessary effort is undertaken, the lifetime of the PWR units should be very long.     

Predictive economic efficiency of combining nuclear power plants with autonomous hydrogen power complex

Currently, the United Energy System (UEC) of Russia is trending in the deficit of peak and half-peak capacity with a simultaneous increase in the number of nuclear power plants (NPPs), which will require the participation of the NPPs in the variable part of the schedule of electrical loads.In addition to the economic need to maintain the high-level utilization rate, there are technological limitations of maneuverability for NPPs.The authors developed an approach to solving this problem by combining with an environmentally friendly energy source – an autonomous hydrogen power complex, which includes thermal batteries and an additional multifunctional low-power steam turbine installation.The developed energy complex can also provide reliable reservation of electricity supply to consumers of their own needs of the nuclear power plant in case of complete blackout of the plant.The feasibility study of the main equipment of the autonomous hydrogen power complex, which is necessary for combining with a two-unit nuclear power plant with WWER-1000, has been evaluated.On the basis of the assessment of the inflation indicators of the Russian economy over the past 11 years, three variants of fuel cost dynamics and tariff rates for electricity (capacity) as well as the size of operating costs, including depreciation deductions to the main equipment, are defined, taking into account the current principles of price formation.The result is a value for accumulated net present value, depending on the ratio of the cost of the half-peak and off-peak electricity at different inflation rates.The positive economic effect of reducing the risk of the core damage accident, replacing the construction of the gas turbine unit as a maneuverable source of electricity in the power grid and increasing the income of the Russian federal budget from the savings of natural gas has been taken into account.The greatest economic efficiency is achieved with maximum projected inflation, which is associated with the maximum rate of discounting and the high rate of growth of electricity tariffs.Reducing the risk of the core damage accident ensures that the proposed approach is competitive in all the inflation options under consideration and the ratio of electricity tariffs.     

ASME核电材料升级浅析

本文以国内某大型装备制造企业ASME核电N、NPT、NS换证为背景,主要介绍了非核级材料(USM级)升级为核级材料的过程,以钢管及钢板举例详细描述了库存材料的调用过程,材料提货供应单(MSO)、材料试验报告(CMTR)的编制方法及在编制过程中的注意事项     

Reference stress method for evaluation of failure assessment curve of cracked pipes in nuclear power plants

In order to obtain a precise failure assessment curve (FAC) in the R6 defect assessment procedure, it is necessary to evaluate the J-value of cracked components. The reference stress method can be used for estimating J-values. However, the accuracy of estimation depends on the limit load used for evaluating the reference stress. In this study, the applicability of several limit load solutions was investigated through comparison with the results of elastic-plastic finite element analyses (FEA). A pipe containing a circumferential surface crack was analyzed under pure bending load. Six materials used in nuclear power plants were assumed. It was shown that the reference stress method is valid for FAC evaluation. The maximum non-conservativeness caused by using the reference stress method is less than 20% compared to the results obtained by FEA.     

Green's function approach for crack propagation problem subjected to high cycle thermal fatigue loading

An efficient numerical approach using Green's function for the analysis of crack propagation under thermal transient load has been presented. The present approach based on multi-Green's functions pre-determined for each stage of the incremental crack growth substantially shortens the calculation time of the stress intensity factor (SIF) ranges. It was shown that the Green's function method (GFM) can be efficiently used to evaluate not only thermal stresses for fatigue analysis but also the SIF for crack propagation analysis. The crack propagation analysis results have been compared with those of the actual observation for the piping structure subjected to thermal striping load in a liquid metal fast breeder reactor. It was shown that the function determined at a fixed temperature can be applied to a relatively wide range of temperatures because of the compensation effect of the material properties, that is, some properties increase while the others decrease as the temperature increases.     

Overview of JSME flaw evaluation code for nuclear power plants

A Japanese flaw evaluation code for nuclear power plant components has been developed at the Japan Society of Mechanical Engineers (JSME). The code prescribes methods for the evaluation of flaws, which are detected during inservice inspection for pressure vessels and pipes in nuclear power plants. This paper describes the basic flow chart, methods of evaluation and allowable flaw sizes for acceptance standards and criteria, including comparisons with the ASME Code Section XI.     

On line fatigue life monitoring methodology for power plant components

Fatigue is one of the most important aging effects of power plant components. Information about fatigue helps in assessing structural degradation of the components and so assists in planning in-service inspection and maintenance. It may also support the future life extension programme of a power plant. In the present paper, the development of a methodology for on line fatigue life monitoring using available plant instrumentation is presented. The Green's function technique is used to convert plant data to stress-time data. Using a rainflow cycle counting method, stress-time data are analysed and the fatigue usage factor is computed from the material fatigue curve. Various codes are developed to generate Green's functions, to convert plant data to stress-time data, to find the fatigue usage factor and to display fatigue information. Using the developed codes, information about the fatigue life of various components of a power plant can be updated, stored and displayed interactively by plant operators.

Three different case studies are reported in the present paper. These are the fatigue analyses of a thick pipe, of a nozzle connected to a pressure vessel and of a reducer connecting a heat exchanger to its piping system.     

Analysis of earthquake management design for nuclear power plants (NPPs) incorporated with artificial intelligence (AI) method

It has been studied to analyze the operations in nuclear power plants (NPPs) where the human error could make a trigger to the nuclear disaster following the earthquake in South Korea. The earthquake warning system and its related control algorithm are modeled by the machine learning (ML) of artificial intelligence (AI) where the neural networking is done as a major role. The AI-based control system could give the very good performance in the earthquake incident which is shown by the system dynamics (SD) based simulations. Hence, the nuclear safety system needs the AI based alarming technology which could be a much more advanced control system incorporated with the conventional multiple-barrier concept in NPPs.     

Environmental and social issues of site choice for nuclear power plants

USA legislation now requires applicants for construction permits or operating licences to provide information about environmental impacts their activities might have. In this article the author suggests that individual cost-benefit analyses, while an improvement on traditional methodology, could be more economic by establishing general rules through standardisation of plant design.     

A portfolio analysis model of the demand for nuclear power plants

Electric utilities are characterized as timid risk averters that select coal or nuclear plants or both, where the levellized cost of each is characterized by considerable risk. A portfolio selection model is developed to explain the historical demand for nuclear reactors by region. Some qualitative policy implications are derived with respect to the DOE's objective of reviving the nuclear power market.     

Cost evaluation of two potential nuclear power plants for hydrogen production

Hydrogen is recognized as one of the most promising alternative fuels to meet the energy demand for the future by providing a carbon-free solution. In regards to hydrogen production, there has been increasing interest to develop, innovate and commercialize more efficient, effective and economic methods, systems and applications. Nuclear based hydrogen production options through electrolysis and thermochemical cycles appear to be potentially attractive and sustainable for the expanding hydrogen sector. In the current study, two potential nuclear power plants, which are planned to be built in Akkuyu and Sinop in Turkey, are evaluated for hydrogen production scenarios and cost aspects. These two plants will employ the pressurized water reactors with the electricity production capacities of 4800 MW (consisting of 4 units of 1200 MW) for Akkuyu nuclear power plant and 4480 MW (consisting of 4 units of 1120 MW) for Sinop nuclear power plant. Each of these plants are expected to cost about 20 billion US dollars. In the present study, these two plants are considered for hydrogen production and their cost evaluations by employing the special software entitled “Hydrogen Economic Evaluation Program (HEEP)” developed by International Atomic Energy Agency (IAEA) which includes numerous options for hydrogen generation, storage and transportation. The costs of capital, fuel, electricity, decommissioning and consumables are calculated and evaluated in detail for hydrogen generation, storage and transportation in Turkey. The results show that the amount of hydrogen cost varies from 3.18 $/kg H₂ to 6.17 $/kg H₂.     

Market-based congestion management in electric power systems with increased share of natural gas dependent power plants

The paper addresses market-based congestion management (MBCM) in electric power systems taking into account the constraints of the electric power system (EPS) and the natural gas system (NGS). The proposed method is based on the countertrade methodology, where the system operator performs minimum-cost redispatching according to bids from generators and loads. The EPS is presented by the DC model for power flow calculation, which uses power transfer distribution factors (PTDFs) to describe the relation between generators/loads and line-power flows. The proposed solution applies the Benders decomposition method to decouple the problem into a master problem and subproblem. The master problem includes the bid-based redispatching for congestion relief and the EPS feasibility check. The subproblem checks the NGS operation feasibility when gas-fired generating units are redispatched in the master problem. Any NGS violations from the subproblem are incorporated into the master problem as power constraints for the next iteration of congestion management. The master problem is solved by linear programming. The NGS is presented in a nonlinear model and its feasibility check is performed using successive linear programming. Case studies illustrate the applicability of the proposed congestion management method on simple test models of the EPS and the NGS.     

An improved method for hydrogen deflagration to detonation transition prediction under severe accidents in nuclear power plants

This work proposed a new method for prediction of hydrogen Deflagration to Detonation Transition (DDT) on the basis of oxygen concentration in the presence of inerting diluents. Whereas previously, the traditional criterion for deflagration to detonation transition hypothesized an unchanged air composition, it now seems appropriate to question the assumption and consider possible situations in which the presence of inerting gas components incapacitates the old criterion for applications. Under some circumstances (severe accidents in nuclear power plants), hydrogen may be massively generated by intense chemical reactions between zirconium cladding and overheated coolant in the nuclear reactor vessel. In order to prevent hydrogen explosions, Passive Autocatalytic Recombiners (PARs) that mitigate hydrogen risk by hydrogen oxidations have been implemented in the nuclear energy industry worldwide. It consumes a large amount of oxygen as the reactant and gives rise to an increased ratio of inert gas nitrogen to oxygen in the air, the product of which, water mist, also alleviates explosion hazards. The new method addressed on the variation of oxidant volume fraction and proposed new parameters: the equivalent air and the equivalent inert gases concentrations in deflagration to detonation transition criterion. The HYDRAGON code, that has been specially developed for hydrogen analysis in nuclear power plants, implemented both new and original criteria and has been applied to assessments. Close agreements between numerical simulations and a large number of experimental data sets: a wide variety of fuel gases and inert diluents, suggested that such new technique was viable and applicable to predict deflagration to detonation transition for various combustible gases. A hydrogen risk analysis of an advanced pressurized water reactor using the new method was also demonstrated in this paper.     

Future economy of electric power generated by nuclear and coal-fired power plants

The available literature (1969–1978) on estimated and predicted costs of nuclear and coal-fired power plants has been examined. The complexity and difficulty of predicting the nuclear power economy are discussed. Scenarios are developed for various capacity factors and fixed charge rates to predict the national electric power economy generated by nuclear and coal-fired power plants between 1979 and 1993.     

Evaluating replacement project of nuclear power plants under uncertainty

This paper investigates the valuation of a replacement project of nuclear power plants under the deregulated electricity market. The replacement project consists of two components: the decision to decommission an existing plant and the decision to construct a new plant. In the replacement project, the decommissioning decision should be made considering not only the profitability of the existing plant but also the profitability and costs of the construction of the new plant. Real options theory is used to determine the optimal timing of the decommissioning and construction. In order to examine the effect of decommissioning time and decision making one, we consider a time-lag for these decision making times. We show the dependence of the replacement project value on uncertainty and time-lag.     

Fracture toughness of weld metals in steel piping for nuclear power plants

To determine toughness behaviour of dissimilar welds in steel piping and obtain data to evaluate Leak-Before-Break for these welds, an experimental study on fracture toughness was carried out. This paper provides Charpy impact properties and fracture toughness data of base and weld metals of dissimilar welds in nuclear piping.