Boron‐free small modular pressurized water reactor design with new burnable absorber

This paper presents a preliminary design of a Small Modular Pressurized Water Reactor (SMPWR) aimed at boron‐free operation which can reduce the size of a nuclear power plant (NPP) and the amount of liquid radioactive waste, and also reduce the corrosion issues caused by boric acid in the coolant. The design parameter limits, such as reactivity swing, axial offset (AO), 3D pin peaking factor (Fq), and the required shutdown margin, have been established for the boron‐free SMPWR. Furthermore, a new ring type of burnable absorber (R‐BA) with Zr–¹⁶⁷Er is adopted as a burnable absorber (BA) and HfB₂ is adopted as a control rod material to satisfy those design limits without liquid boron. Optimal fuel assemblies (FAs) and loading patterns have been searched through a sensitivity study, and the excess reactivity control capacity and design requirements have been demonstrated to be satisfactory. Copyright © 2016 John Wiley & Sons, Ltd.     

核电厂用超高分子量聚乙烯喷嘴研发与应用

  目的  为解决核电厂核安全3级循环水过滤系统（CFI）喷嘴冲刷磨蚀及腐蚀问题，采用超高分子量聚乙烯(UHMWPE)开发了一种耐腐蚀、耐磨的喷嘴。  方法  通过对重要加工工艺参数测试，固化了喷嘴制造加工工艺，为验证所开发的喷嘴耐磨性及水力性能，进行材料本体耐磨试验，并模拟核电厂运行条件开展基于研发产品的冲刷和水力试验。  结果  试验结果表明:UHMWPE喷嘴的耐磨性能优异，高于传统材料；可以适应核电厂高速冲刷的需求，水力性能亦可满足核电厂的要求。  结论  UHMWPE喷嘴投入运行一年半，经持续运行，喷嘴未发现冲刷变形和腐蚀现象，运行效果优异。因此，采用超高分子量聚乙烯材料制备核电厂CFI系统喷嘴是可行的，可替代原有的进口尼龙喷嘴。     

Leak-Before-Break criteria and strength monitoring implementation impact on in-service inspection of RBMK primary circuit components

Major scientific and technical tasks of strength monitoring and surveillance in NPP RBMK operation are considered proceeding from the present-day requirements to safety insurance based on the circuit integrity concept.

The application of the “Leak-Before-Break” Concept in the most complete and systematic definition corresponding to the approaches adopted in the U.S.A. will permit, in the case of success, to assess the compliance of RBMK primary circuit components with still more rigid requirements to the integrity and safety in comparison with the regulatory requirements acting at present in the R.F. nuclear industry.

Procedures for evaluation of allowable size defects in pipelines with Dÿ800 depending on the loading levels are viewed. It is shown that the application of the LBB Concept criteria and the implementation of a strength monitoring system as a means of continuous operation quality control permit to assess the requirements to the sensitivity of metal control devices and to support NPP utilities to optimize ISI schedule.     

Natural circulation with DOWTHERM RP and its MARS code implementation for molten salt‐cooled reactors

Recently, molten salt has received attention as a promising coolant for advanced nuclear reactors, especially for fluoride salt‐cooled high‐temperature reactor. The heat transfer characteristics of molten salt provide great advantages for application as a primary coolant, because of its superior performance in terms of sustainability, economics, safety, and reliability compared with gas coolant. However, understanding the thermal‐hydraulic characteristics of molten salts by experimental method is difficult because of its high‐temperature corrosion and toxicity issue. Therefore, oil fluids were introduced as simulants for studying the heat transfer phenomena of high Pr (Prandtl number) molten salts. In this study, a scaled‐down experiment using simulant oil was conducted, and scaling laws were applied to investigate a single‐phase natural circulation, which is important in nuclear reactors as a part of their passive safety. DOWTHERM RP (Diaryl Alkyl) was considered as a heat transfer simulant in this study because it matches the relevant dimensionless numbers (Prandtl number, Ra, Grashof number, Reynolds number, etc.) with those of molten salt. Prior to the experiment, the thermophysical properties of both the liquid and vapor phases of DOWTHERM oils were implemented into thermal‐hydraulic system analysis code or multi‐dimensional analysis of reactor safety code, to enable simulation and further study of the molten salts. Then, natural circulation experiments were conducted with the scaled rectangular loop, to establish similarity and experimental feasibility. For the validation, two different codes (multi‐dimensional analysis of reactor safety and computational fluid dynamics (CFD) were used to simulate the same natural circulation loop. From the experimental data, new heat transfer correlation for a single‐phase natural convection was developed, and the existing heat transfer correlations were compared. Copyright © 2016 John Wiley & Sons, Ltd.     

Experiences in using PRA as an operational tool

The Probabilistic Risk Assessment (PRA) of Koeberg Nuclear Power Station has been used for a number of years to support operation decision making. The principle aim of this risk assessment of Koeberg is to determine the probability of a severe accident under varying operating conditions. This plant model is used by ourselves and our licensing authority to assess nuclear safety issues. Through this process, considerable practical experience has been gained in using a “living” PRA to improve plant safety and performance. This paper presents some of the insights obtained in using reliability engineering in such a dynamic way and demonstrates that by developing and using the “living” PRA considerable safety and financial gains can be obtained. These insights mainly concern the prerequisites required before optimal use of a “living” PRA can be made. Other insights concern how PRA results are best presented and interpreted. Finally, examples are presented of occurrences when PRA was used to aid operating decisions.     

The effect of ageing on the anodic corrosion of Pb-Sb alloys

Information on the changes that may be expected in the corrosion resistance of battery grids of Pb-4% Sb and Pb-6% Sb alloys as a function of time is pThe influence of ageing time (at 20 °C) upon the corrosion weight losses is accounted for by the microstructural changes that take place in the alloy     

Prospect of RBMK-NPPS strength monitoring system on-line module development

System for strength monitoring and residual lifetime (SMS) assessment of NPP equipment makes it possible to improve safety and effectiveness of operation.

According to SMS concept it includes two main modules: for on-line data acquisition and diagnostic and for off-line date processing and lifetime assessment.

Algorithm for RBMK SMS on-line module is proposed to be based on the basis of “DASHA” expert system shell.

Universal expert shell “DASHA” was created using the original matrix method of image identification theory and can be used for on-line diagnostic system development for any complex technological object of arbitrary physical nature.     

Survey of operating experience to identify structural degradation of nuclear power plant components

An assessment was performed by the Nuclear Operations Analysis Center (NOAC) staff at Oak Ridge National Laboratory of the information available from operation of United States nuclear power plants in their Licensee Event Reports (LERs) which is pertinent to identifying failures due to age-related degradation. LERs from commercial power plants submitted from 1969 to 1982 were surveyed, yielding 3098 events that were considered to be age-related failures. Wear, corrosion, fatigue, vibration, stress corrosion, and erosion were identified as the structural failure cause mechanisms in over half of the events. The study contains data on failed components, the age-related failure mechanisms responsible, the severity of the failures, and the failure detection methods of failures from possible age-related causes.     

Increasing NiMH battery cycle life with oxygen

Nickel-Metal Hydride batteries (NiMH) have long cycle life. But in the end corrosion of the metal hydride is detrimental for life expectancy. Corrosion reduces the metal hydride capacity, but more severely it consumes water in the electrolyte resulting in increased internal resistance, which is the main cause for cell failure.The corrosion, further, evolves hydrogen, causing an unbalance between anode and cathode, leading to premature internal pressure increase when the cells are approaching end of charge. This accelerates the drying out, if the cells vent through the safety valve.In this study, a controlled addition of oxygen was used to rebalance the electrodes and replenish the electrolyte – as the added oxygen reacts with hydrogen that was formed during the corrosion process. Thus, the two most detrimental factors in cell ageing can be mitigated. To fully restore the electrolyte content as well as electrode balance, both oxygen and hydrogen are needed to compensate for the loss to hydroxide ions OH^? formed in the corrosion process. A proper optimization of the gas additions combined with a cell design including an excess amount of MH-alloy to compensate for the corrosion can substantially increase the cycle life of NiMH batteries.     

Downscaling a supercritical water loop for experimental studies on system stability

In industry, supercritical water is being used as e.g. separation agent, solvent or coolant due to the unique fluid properties near the critical point. This has lead to the proposal for a nuclear reactor based on supercritical water, operating at a pressure of 25 MPa and bulk temperatures between 280 °C and 500 °C. The large change of the water density in such a reactor may cause the system to become thermal-hydraulically unstable. Numerical as well as experimental investigation of this phenomenon is therefore essential. The rather high pressure, temperatures and power significantly push up the costs of an experimental facility. For this reason, we propose a scaling procedure based on Freon R-23 as the working fluid so that (i) pressure, power and temperatures are significantly reduced and (ii) the physics determining the dynamics of the system are almost completely preserved. Practical issues, such as the onset of deterioration of heat transfer, are touched upon as well.     

Study of ageing of laminates and its effects on wind turbine blade deflection

Some wind turbines have exceeded their nominal design service life and are continuing their operation with periodic inspections and maintenance. In the case of rotor blades, the reliability of the inspection is very limited because of the blade structure that comprises laminates and sandwich structures, which are very difficult to monitor. For this reason, wind farm owners are searching for technologies or approaches that will guarantee a safe operation of their wind turbines after the design life has elapsed. The main objective of this paper was to investigate whether detection of ageing of wind turbine blades using deflection as key parameter is feasible using commercial equipment. The paper is divided in three phases. In phase 1, the effect of ageing on a new UD‐0° glass fibre with high moduli was obtained. Using these results and bibliography data, a theoretical study was performed in phase 2 to determine the magnitude of blade deflection along its lifetime due to material ageing. Finally, in phase 3, in‐field deflection measurements where performed on a wind turbine blade to evaluate the utility and limitations of commercial equipment for the detection of blade ageing. It was concluded that material ageing could result in an increase in blade deflection under self‐weight that can be detected using commercial measurement equipment. These results can be used by wind farm owners in their O&M strategies to monitor blades over time and decide whether they should be repaired or replaced.     

Quantitative and qualitative analysis of safety parameters in nuclear power plants

After the Fukushima accident, it is necessary to develop some technique that can monitor the progression of severe accidents in nuclear power plants (NPPs). It is therefore very important for an operator to monitor safety related parameters for the diagnosis of severe accidents and to manage it properly. So to monitor and to check the availability of plant instrumentation during severe accidents, this paper presents quantitative and qualitative analyses of safety parameters by using online risk monitor system (ORMS). An ORMS considers the increasing potential for failure for a working component due to aging, which appears in the form of component's performance degradation. ORMS therefore requires a continuous feedback regarding performance and failure probabilities of components, which directly or indirectly contributes to the failure of a system. ORMS has been designed to automatically update the online risk models and reliability parameters of equipment. A case study of emergency diesel generator (EDG) of Daya Bay NPP has been performed, and operational failure rate and demand failure probability of EDG have been calculated with the help of ORMS. The results of ORMS are well matched with data obtained from Daya Bay NPP. ORMS can support in decision‐making process for operators and managers at NPPs. Copyright © 2013 John Wiley & Sons, Ltd.     

Comprehensive assessment of system efficiency and competitiveness of nuclear power plants in combination with hydrogen complex

The strategy provides construction and commissioning of a number of new nuclear power units for the development of nuclear energy in Russia. The share of nuclear power plants increase in the energy systems of Russia is predicted from 19 to 22% in the future, up to 2050. Nuclear power plants planned to involve in the primary frequency control at the same time. All these circumstances exacerbate the problem of providing nuclear power plants with a basic electrical load in the night period, including during the daily period. The energy strategy of Russia provides for the production of hydrogen by low-carbon methods, one of which is water electrolysis using nuclear power. Hydrogen production is included in the development strategy of the at operating Russian NPPs. Hydrogen production planned at the Kola NPP by water electrolysis. Thus, the article provides a rationale for the effectiveness of combining nuclear power plants with a hydrogen complex based on the production of hydrogen by electrolysis of water. The effectiveness substantiated of the new principle of combination with overheating of the working fluid steam turbine cycle of the NPP taking into account the safety of handling hydrogen. A new system proposed for the combustion of hydrogen in oxygen, which makes it possible to overheat the working fluid of the NPP steam turbine cycle with undissociated steam, which significantly reduces the content of unreacted hydrogen in the working fluid flow. In addition, a system was developed and proposed for removing unreacted hydrogen and oxygen from the steam phase of the working fluid of the NPP steam turbine cycle. Thermodynamic and technical-economic new estimates are presented and analyzed of the efficiency of combining NPP with a hydrogen complex.     

Numerical investigation of light gas release,stratification and dissolution in TH22 test facility using 3-D CFD code GASFLOW-MPI

An accurate prediction of the hydrogen behaviors in the accident and management process is a crucial topic for both the hydrogen safety assessment and safety analysis in the confined enclosure like the containment of the nuclear power plant (NPP). Hence, the hydrogen behaviors including the transient light gas release, stratification and dissolution in the TH22 test facility for the NPP containment are analyzed and compared using the 3-D CFD code GASFLOW-MPI in this study. In this paper, the light gas helium is adopted as a substitute for the hydrogen in the calculations in accordance with the experiment. Firstly, the detached eddy simulation (DES) turbulence model, 3-D numerical model and experiment setup are introduced. Then, the hydrogen behaviors with the GASFLOW-MPI including the light gas release, stratification and dissolution are analyzed and validated with the experiment data. In addition, the velocity profiles, light gas concentrations, dimensionless numbers and temperature distributions are evaluated for the characteristics of the hydrogen behaviors. The results indicate that the calculation results agree well with the experiment data. Foremostly, the relative errors between the calculation results and experiment data during the phase of the dissolution of the light gas cloud are within 11.9%. Meanwhile, the relative errors of the time for the complete dissolution during the phase of the dissolution of the light gas cloud are within 5.0%. For the light gas release and stratification phase, the jet flow dominates as the Froude (Fr) number exceeds 10 during the time t = 600 s–800 s. Additionally, the time averaged centerline velocity and light gas concentration after the potential core region decay with a slop of 1/z which coincide with the theoretical jet limit. Lastly, the light gas concentrations and temperature distributions in all three phases are captured clearly with the GAFLOW-MPI. It demonstrates that the GASFLOW-MPI can accurately described the details of the related hydrogen behaviors in the accident and management process in the confined enclosure like the NPP. This paper can provide guidance for the numerical computation of the hydrogen safety issues in the confined space.     

Stress corrosion cracking of nuclear reactor pressure vessel and piping steels

This paper presents an extensive investigation of stress corrosion cracking of nuclear reactor pressure vessel and piping steels exposed to hot water. Experimental fracture mechanics results are compared with data from the literature and other laboratories. Thus a comprehensive overview of the present knowledge concerning stress corrosion crack growth rates is provided. Several sets of data confirm that ‘fast’ stress corrosion cracks with growth rates between 10⁻⁸ and 10⁻⁷ m/s and threshold stress intensities around 20 MN m^−3/2 can occur under certain conditions. However, it appears possible that specific environmental, mechanical and metallurgical conditions which may prevail in reactors can result in significantly lower stress corrosion crack growth rates. The presently known stress corrosion crack growth rate versus stress intensity curves are discussed with emphasis on their usefulness in establishing safety margins against stress corrosion cracking of components in service. Further substantial research efforts would be helpful to provide a data base which permits well founded predictions as to how stress corrosion cracking in pressure vessels and piping can be reliably excluded or tolerated. It is emphasized, however, that the nucleation of stress corrosion cracks (as opposed to their growth) is difficult and may contribute substantially to the stress corrosion free service behavior of the overwhelming majority of pressure vessels and pipes.     

The relation of mineral composition to slagging,fouling and erosion during and after combustion

Inorganic matter in coal has been a major cause of problems in fuel-burning energy-conversion systems since the dawn of the Industrial Revolution. Even in the earliest days, hand-fired boilers were limited in their steaming capacity by the formation of clinkers in the fuel bed. Today, many large coal-burning power plants are restricted in steam generation by accumulations of coal ash on heat-receiving surfaces. These deposits not only decrease the rate of heat transfer but they also plug gas passages and lead to metal wastage by erosion and corrosion. As a result, coal-burning boiler furnaces must be appreciably larger, and hence more costly, than gas- or oil-fired steam generators, and operating practices are more critical when coal is the source of energy rather than “cleaner” fluid fuels.The intent here is to describe the characteristics of the mineral matter in coal, to show how the non-combustible material behaves at the high temperatures of boiler furnaces, to explain how coal ash can lead to metal wastage by erosion and corrosion, and to review problems in the collection of flyash attributable to ash composition.     

Experimental investigation of an adsorption desalination plant using low-temperature waste heat

Adsorption cycle is a practical and inexpensive method of desalinating the saline and brackish water to produce potable water for both industrial and residential applications. As compared with the commercial desalination methods, the adsorption technology has the unique advantages such as (i) the utilization of the low-temperature waste heat, (ii) low corrosion and fouling rates on the tube materials due to the low-temperature evaporation of saline water, (iii) and it has almost no major moving parts which renders inherently low maintenance cost. In addition, the adsorption cycle offers two important benefits that are not available to the existing desalination technologies; namely, (i) a two-prong phenomenal barrier to any “bio-contamination” during the water generation process as compared with existing methods and (ii) the reduction in global warming due to the utilization of low-temperature waste heat which otherwise would have been purged to the atmosphere. This paper describes an experimental investigation and the specific water yields from a four-bed adsorption desalination plant is presented with respect to major assorted coolant and feed conditions.     

Assessment methods of material ageing using Sdobyrev''s creep rupture model

The physical aspects of the activation energy, in higher and high temperatures, of the metal creep process were examined. The research results of creep-rupture in a uniaxial stress state and the criterion of creep-rupture in biaxial stress states, at two temperatures, are then presented. For these studies creep-rupture, taking case iron as an example the energy and pseudoenergy activation was determined. For complex stress states the criterion of creep-rupture was taken to be Sdobyrev's, i.e. σ_red = σ₁ β + (1 − β)σ_i, where: σ₁-maximal principal stress, σ_i-stress intensity, β-material constant (at variable temperature β = β(T)). The methods of assessment of the material ageing grade are given in percentages of ageing of new material in the following mechanical properties: 1) creep strength in uniaxial stress state, 2) activation energy in uniaxial stress state, 3) criterion creep strength in complex stress states, 4) activation pseudoenergy in complex stress states. The methods 1) and 3) are the relatively simplest because they result from experimental investigations only at nominal temperature of the structure work, however, for methods 2) and 4) it is necessary to perform the experimental investigations at least at two temperatures.     

Analysis of the effects of outdoor and accelerated ageing on the optical properties of reflector materials for solar energy applications

Lifetime tests of solar reflector materials are eligible prior to application, to prove the stability of the optical properties. In this work, six reflector materials were aged outdoors and in a climatic test chamber. The surfaces of the samples were inspected using profilometry and optical microscopy. The total and specular reflectance spectra were measured using spectrophotometry and the weighted solar reflectance values were calculated before and after ageing. Reflectors of silvered glass, anodised aluminium, thin film-coated anodised aluminium, and lacquered rolled aluminium withstood accelerated testing well, while a laminated evaporated aluminium reflector, which was specular initially, became diffuse. Laminated and lacquered reflectors withstood outdoor ageing better than expected from accelerated ageing and better than unprotected thin film-coated and anodised aluminium, which degraded significantly outdoors. Thus, optical degradation depends on climatic conditions and on the protective layer, if applicable. The discrepancy between results from outdoor and accelerated ageing shows that a thorough understanding of corrosion processes is necessary for drawing conclusions about long-term performance from accelerated ageing tests.     

Japan''s nuclear energy policy: from firm commitment to difficult dilemma addressing growing stocks of plutonium, program delays, domestic opposition and international pressure

Since 1956, Japan has been on a path to reduce its dependence on foreign energy sources through the development of nuclear power. This paper examines the origins of this commitment, the changing social issues and the current dilemma Japan faces regarding the future of its nuclear energy policy and its efforts to overcome the domestic and international pressures to ensure safety and security.

Galvanized by international initiatives and further motivated by the oil crises in the 1970s, Japan's commitment to develop a closed nuclear fuel cycle, one which reprocesses fuel from thermal reactors for use in advanced fast breeder reactors, has remained resolute. However, program delays, international security concerns over the plutonium, a weapons-grade nuclear material and one of the products of reprocessing, and increasing public opposition to various components of the Atomic Energy Commissions’ Long-Term Program for Development and Utilization of Nuclear Energy, have put pressure on the government to resolve these issues.

The commitment to develop the technology on one hand is commendable however it has contributed to the dilemma the Japanese nuclear industry now faces: a growing stockpile of plutonium and no readily available means of reducing it. With growing public involvement, finding a straightforward technology solution is increasingly difficult.

In 1995, an accident at Monju, one of the first prototype fast breeder reactors in Japan, prompted the Commission to initiate the first Roundtable Conference. The purpose of the Conference was to open the policy making process in an effort to determine a “national consensus” on nuclear energy. Further accidents and on-going opposition further slowed the implementation of the Program, however, in the latest Program, released in 2000, the Commission attempts to address these issues while building in a new style of flexibility in order to allow for greater options in the future.