Coolant Environments Research Articles

Investigation on Analysis Method of Environmental Fatigue Correction Factor of Primary Coolant Metal Materials in LWR Water Environment

The environmental fatigue correction factor (Fen) is mainly used to analyze the influence of the coolant environment on the fatigue life of primary metal materials. Because the calculation of the transformed strain rate is related to the stress history of the component structure, how to determine the strain rate is the most critical step in calculating the Fen. The approaches of the detailed method were given by the Electric Power Research Institute (EPRI) guidelines and RCC-M-2017 Edition Section VI- RPP No. 3 separately, so a gap analysis was performed between the two methods. Furthermore, another average method was also proposed to determine the average strain rate and strain range. Based on the analysis benchmark provided in the EPRI guideline, a simple case study was performed to account for the effect on the fatigue life in applications with different strain rate approaches and different Fen expressions. Finally, two industry case studies were also completed, including on materials of low alloy steel, austenitic stainless steel, and nickel-base alloy. We suggest adopting a more accurate detailed method, and its methodology is recommended to provide more reasonable solutions.

Research On Optimization Method of Fatigue Analysis for Nuclear Pipeline

The initial design life of nuclear power plant is 40 years. In 60 year life extending license application, the fatigue of component should be evaluated under the influence of the fatigue factors of the pressurized water reactor coolant environment. Because the original design used a more conservative analysis method, the result could not meet the requirement of Cumulative usage fatigue factor of RCC-M. An optimizing analysis method is studied, and as an example of application, optimizing fatigue analysis of Safety Injection Nozzle of Main Coolant Line is performed. The evaluation results show that the optimized fatigue analysis results meet the requirements of RCC-M.

Experimental studies on cryogenic CO2 face milling of Inconel 625 superalloy

ABSTRACT In this study, face milling operation was carried out on an Inconel 625 superalloy. About 27 experiments (L27) were conducted using Design of Experiments (DOE), which comprised three levels of cutting speed (V c ) and feed rate (f z) with a constant cutting depth (ap ). The study included three coolant environmental conditions such as no coolant (dry), normal coolant (wet) and cryogenic CO2 coolant. The output responses such as cutting temperature (T s), cutting forces (Fx, Fy and Fz ) and surface roughness (R a) were observed during the experiments. The results were optimized using the TOPSIS technique with ANOVA tests. The optimization results of highest closeness coefficient (Ci ) value indicated the lowest level of cryogenic CO2 coolant environment and the input parameters were the cutting speed (V c) 80 m/min and feed rate (f z) 0.05 mm/tooth. The optimization results of the highest closeness coefficient (Ci ) value were at cutting speed (V c) 80 m/min, feed rate (f z) 0.05 mm/tooth in cryogenic CO2 coolant environment. The findings indicated that cryogenic CO2 was both environmentally harmless and the best choice in comparison with dry and wet coolant.

Membrane bulge test rig for irradiation-assisted stress-corrosion cracking

During their service in a nuclear power plant, structural materials are subject to high temperature, mechanical stress, corrosive coolant environments, and neutron irradiation. The combination of radiation, corrosion and thermo-mechanical loading represents a unique environment that materials must endure: radiation can significantly alter the material’s thermo-mechanical performance and the lifetime of a component. The conditions under which this happens are difficult to study and normally necessitate nuclear reactor experiments followed by post-irradiation examination in hot cells, which renders investigations complex, time consuming and expensive. While few attempts have been made to study the combined effects of radiation and corrosion with lead bismuth eutectic [1] or molten salts [2] none of these experimental set-ups were designed to study the combination of corrosion and irradiation together with mechanical loading. Here the development of a miniature test technique is presented where irradiation, corrosion and strain can synergistically be applied on a material in a controlled way. The experiment is based on scaling down the membrane bulge test [3], using liquid lead as a pressure medium at high temperature. Membrane type specimens are made from the structural material to study, with their back side pressurized thereby inducing corrosion and membrane stretching stress while irradiation damage is generated by proton irradiation at the front surface affecting the entire thickness to the back side of the sample. The paper presents the way how the engineering problems related to the combination of corrosion by liquid metal, stress application and irradiation of the sample have been addressed.

Weibull and Bootstrap-Based Data-Analytics Framework for Fatigue Life Prognosis of the Pressurized Water Nuclear Reactor Component Under Harsh Reactor Coolant Environment

AbstractIn general, the fatigue life of a safety critical pressure component is estimated using best-fit fatigue life curves (S-N curves). These curves are estimated based on underlying in-air condition fatigue test data. The best-fitting approach requires a large safety factor to accommodate the uncertainty associated with large scatter in fatigue test data. In addition to this safety factor, reactor component fatigue life prognostics requires an additional correction factor that in general is also estimated deterministically. This additional factor known as the environmental correction factor Fen is to cater the effect of the harsh coolant environment that severely reduces the life of these components. The deterministic Fen factor may also lead to further conservative estimation of fatigue life leading to unnecessary early retirement of costly reactor components. To address the above-mentioned issues, we propose a data-analytics framework which uses Weibull and Bootstrap probabilistic modeling techniques for explicitly quantifying the uncertainty/scatter associated with fatigue life rather than estimating the lives based on a best-fit based deterministic approach. We assume the proposed probabilistic approach would provide the first hand information for assessing the maximum and minimum effects of pressurized water reactor water on the reactor component. In the discussed approach, in addition to the probabilistic fatigue curves, we suggest using a probabilistic environment correction factor Fen. We assume the probabilistic fatigue curve and Fen would capture the S-N data scatter associated with the bulk effect of material grades, surface finish, strain rate, etc. on the material/component fatigue life.

A comprehensive investigation on the effect of flood and MQL coolant on the machinability and stress corrosion cracking of super duplex stainless steel

The poor machinability of super duplex stainless steels (SDSS) tends to generate detrimental tensile residual stresses that affect the service life of the component. Therefore, developing an efficient machining strategy to machine these components without any subsurface modifications is necessary. This work emphases on a detailed analysis of machinability and stress corrosion cracking resistance (SCC) of SDSS under different coolant environments (Dry, Flood, Minimum quantity lubrication). The cutting performance was evaluated using the machinability indicators such as tool wear, cutting force, surface finish, morphology of chips and residual stress. The chip morphology and residual stress results indicated that the thermally assisted deformation highly influences the machining of SDSS under all coolant environments. The overall machinability results revealed that MQL provided better performance than the other coolant and lubrication methods. To assess the SCC resistance, all the machined samples were subjected to SCC test under the chloride environment. The machined samples under MQL environment was observed with low surface crack density. This is due to presence of lower tensile residual stress with less surface defects. It was also observed that MQL samples exhibits lower localized corrosion (i.e) pit formation on the surface. These results clearly demonstrate that MQL is a recommended cooling and lubrication condition for the efficient machining of SDSS and to improve service life of the component.

Fatigue model of domestic 316LN steel in simulated primary coolant environment of CAP1400

Fatigue tests of domestic 316LN were carried out in the simulated primary coolant environment of CAP1400 (the advanced 3rd generation nuclear power plants developed in China). Effects of temperature, strain rate and dissolved oxygen (DO) on fatigue life were analyzed. Based on the results, a fatigue model was developed. Fatigue life in primary coolant environment increases logarithmically as the temperature decreases from 321 ℃ to 150 ℃. When the temperature decreases to 150 ℃, fatigue life in primary coolant environment is very close to that in air environment. Fatigue life increases as the strain rate increases from 0.004%/s to 1%/s. After the strain increases to more than 0.4%/s, fatigue life in primary coolant environment is very close to that in air environment. Effect of DO on fatigue life in primary coolant environment is not obvious in the DO range of 0.005 ppm to 8 ppm. Compared with NUREG6909 model, the present fatigue model is more accurate in lifetime prediction of domestic 316LN.

Machining in high pressure coolant environment – a strategy to improve machining performance: a review

Machining is a commonly preferred production process. Machining with high pressure coolant, cryogenic coolant, or atomised coolant spray are the latest techniques investigated by the researchers to improve the productivity. Researchers have performed the work on various aspects of machining using high pressure coolant. Researchers have investigated effect of coolant related parameters, machining parameters, tool related parameters on surface finish, dimensional accuracy, tool wear, tool life, forces, chip morphology, tool and work piece temperature, and wear mechanism during machining of different materials. Researchers have performed the research with regard to coolant type, coolant pressure, flow rate, coolant concentration, and coolant jet direction and come up with interesting and beneficial findings. This paper presents a comprehensive literature review on high pressure coolant strategy in machining of materials with respect to various aspects. The paper presents important findings in this area and pinpoints the issues which should be investigated in future.

Machining in high pressure coolant environment – a strategy to improve machining performance: a review

Machining is a commonly preferred production process. Machining with high pressure coolant, cryogenic coolant, or atomised coolant spray are the latest techniques investigated by the researchers to improve the productivity. Researchers have performed the work on various aspects of machining using high pressure coolant. Researchers have investigated effect of coolant related parameters, machining parameters, tool related parameters on surface finish, dimensional accuracy, tool wear, tool life, forces, chip morphology, tool and work piece temperature, and wear mechanism during machining of different materials. Researchers have performed the research with regard to coolant type, coolant pressure, flow rate, coolant concentration, and coolant jet direction and come up with interesting and beneficial findings. This paper presents a comprehensive literature review on high pressure coolant strategy in machining of materials with respect to various aspects. The paper presents important findings in this area and pinpoints the issues which should be investigated in future.

Machining Performance Investigation of AISI 304 Austenitic Stainless Steel under Different Turning Environments

Environment friendly machining calls for minimizing the use of cutting fluids to reduce their negative impact on environment and operator health. Present experimental work is aimed to investigate machining performance of AISI 304 austenitic stainless steel with PVD coated carbide tool under different turning environments viz. dry, flooded and nanofluid minimum quantity lubrication (NF-MQL). Optimum turning parameters obtained through desirability function optimisation are found as: cutting speed of 160.67 m/min, feed of 0.06 mm/rev and depth of cut of 0.25 mm with predicted tool flank wear of 100.001 μm and surface roughness of 0.509 μm at 0.808 desirability level. Confirmation tests show 3.22% and 3.41% error between predicted and experimental values of Vb and Ra, respectively. Present study has established the superiority of NF-MQL machining over dry and flooded machining. The most salient achievement of this investigation is the reduction of tool flank wear by 32.26% under NF-MQL machining compared to dry machining and 9.68% compared to flooded machining conditions. Similarly, NF-MQL exhibits improvement in surface finish by 34.72% and 7.59% over dry and flooded coolant environments respectively, thus providing a strong basis to replace flooded coolant machining for sustainable future.

Optimization of end milling process of Oil Hardened Non-Shrinking Die Steel (OHNS) under different cutting environment using Taguchi and Response surface methodology (RSM) approach

ABSTRACTIn this paper Response surface methodology (RSM) based multi-objective approach is applied in order to predict optimal machining parameters and better cutting environment for the end milling process of OHNS (Oil Hardened Non-Shrinking Die Steel) using both coated and uncoated carbide tools of 8 mm diameter inserted into an end miller in both dry (without coolant) and wet (milling with coolant) environment. Optimization is carried out using parametric model based on input cutting parameters such as cutting speed, feed rate and depth of cut and exploiting the capabilities of statistical approaches (Taguchi and RSM) in constrained machining. The objective function is to minimize the surface roughness and finding the better end milling tool-type and cutting environment. The optimized parameters carrying the major objective function (minimizing surface roughness) for different tooling and cooling condition is identified. It was observed that the best optimized configuration for end milling of OHNS was found in carbide coated tool in both dry and wet cutting environment.

Research on the Application of Fen for Environmentally Assisted Fatigue Evaluation of the Austenitic SS Pipe Under Combined Transient Loads

Accumulative test data indicate that the effects of the light water reactor (LWR) environment could cause the fatigue resistance of primary pressure boundary components materials to be significantly reduced. Environmentally assisted fatigue (EAF) is the abbreviation of the environmentally assisted fatigue. In 2007, Nuclear Regulatory Commission (NRC) issued RG. 1.207. It was updated in 2014. And, it requires that the effects of LWR environment on the fatigue life reduction of metal components should be considered for new design plants. And it suggests to use environmental correction factor, Fen, to account for EAF. NRC regulation (NUREG), NUREG/CR-6909 (NRC, 2013, “Effect of LWR Coolant Environments on the Fatigue Life of Reactor Materials,” U.S. Nuclear Regulatory Commission, Argonne, IL, Standard no. NUREG/CR-6909), presents the detail Fen calculation formula. Fen is a function of temperature, strain rate, dissolved oxygen level in water, and sulfur content of the steel. Accordingly, Fen calculation will present a comparatively conservative result. Depending on the experience of the primary pressure boundary piping transient operation, Fen varies during each transient. More uncertainty and confusion are raised during the application of the Fen method. The research work in this paper includes: first, the typical character of piping thermal transient is derived based on the existing experience. Second, small specimen EAF tests are conducted depending on the above derived combined loading characters. Then effort is taken to improve the application of the Fen method for the combined multitransient loading conditions. And the results are compared with those of the lowest instantaneous Fen method and equalization of the weighted Fen method. Finally, a designed test plan is presented.

Development of Fatigue Crack Growth Prediction Model in Reactor Coolant Environment

In order to conduct effective and rational maintenance activity of components in nuclear power plants, it is proposed to manage fatigue degradation based on crack size corresponding to an extent of cumulative fatigue effect. This study is aimed at developing a prediction model for fatigue crack growth in simulated reactor coolant environment. In order to investigate influence of reactor coolant environment on crack initiation and crack growth, two-step replica observations were conducted for environmental fatigue test specimens (type 316 stainless steel) subjected to three kinds of strain range. Crack initiation, growth, and coalescence were observed in the experiments. It is clarified that crack coalescence is one of the dominant factors causing fatigue life reduction, and fatigue life reduction depends on crack size and distance of two coalescing cracks. Then, a model was developed for predicting statistical crack initiation and growth behavior. The relationship between dispersion of crack initiation life and strain range was approximated by the Weibull model to predict crack initiation. Then, the statistical crack growth was modeled using the relation of crack growth rate and strain intensity factor. Furthermore, the crack coalescence was taken into account to the crack growth prediction considering the distance between two cracks. Finally, the crack growth curve, which is the relationship between crack size and operation period, was derived through Monte Carlo simulation with the developed model. The crack growth behavior and residual life in the simulated reactor coolant environment can be reviewed by the crack growth curve obtained with crack initiation, and the growth model developed was compared with the fatigue test results.

Customization of the coupled environment fracture model for predicting stress corrosion cracking in Alloy 600 in PWR environment

The coupled environment fracture model (CEFM) has been modified and calibrated to predict crack growth rate (CGR) in Alloy 600 under typical PWR primary coolant conditions. The customized CEFM provides quantitative predictions of the effects of stress intensity factor, hydrogen concentration, yield strength, and temperature on CGR in Alloy 600 in PWR primary coolant environments, as well as explaining the dominating mechanism of stress corrosion cracking (SCC) in this alloy. The importance of the mechanical properties, such as yield strength and stress intensity factor, as identified previously from Artificial Neural Network (ANN) analysis of CGR data in the literature, has been confirmed theoretically. The success in explaining the intergranular stress corrosion cracking (IGSCC) of Alloy 600, argues that the CEFM, which was originally developed to describe IGSCC in sensitized stainless steels, is equally applicable for describing IGSCC in Alloy 600.

High temperature alloys stability testing in impure helium

Abstract Within the national and international research program of materials for advanced nuclear reactors Czech organizations contributed with several tests of metallic alloys. The specimens of the alloys were first exposed in the long term (up to 1500 hours) in simulated advanced gas cooled reactor coolant environment at 750-900 °C. After exposure the degradation of tested materials was explored, especially changes in material microstructure, corrosion damage and corrosion layer composition and in some cases also changes in mechanical properties were observed. In this paper selected results of exposure tests in high temperature helium of alloy 800 H, austenitic steel 316L and high-temperature nickel alloys are presented.

Chromium Coating as a Surface Protection of Zirconium Alloys

Abstract Increasing of nuclear safety, higher demands for longer nuclear fuel campaign and higher levels of burnout are based on improving the properties of zirconium alloys. Protective coatings appears to be a promising way to reduce their chemical reactivity and increase resistance to hydriding. In this work, a thin chromium coating applied to a standard Zr1Nb zirconium alloy was studied using in-situ impedance spectroscopy. Exposure was carried out at a temperature of 280 ° C and a pressure of 8 MPa in a simulated WWER primary coolant environment. The results show that the chromium-coated Zr1Nb alloy is under these conditions oxidized significantly slower than the non-coated alloy.

Technical Note: Corrosion Fatigue Crack Growth of Forged Type 316NG Austenitic Stainless Steel in 325°C Water

Forged Type 316NG austenitic stainless steel is commonly used to fabricate primary coolant pipe in advanced pressurized water reactor systems, but it is subject to corrosion fatigue cracking in primary coolant environments. In this study, the fatigue crack growth of Type 316NG austenitic stainless steel in 325°C water was investigated. The corrosion fatigue effect in 325°C water was mainly correlated to the crack growth rate and load frequency. A maximum Fen (environment corrected factor) value up to 100 was observed at f = 0.005 Hz, ΔK = 13 MPa√m. The dissolved oxygen tended to have little influence on the fatigue crack growth. The crack path was deflected and branched. Most secondary cracks tended to be initiated from grain boundaries.

Corrosion fatigue and microstructural characterisation of Type 316 austenitic stainless steels tested in PWR primary water

Fatigue crack growth experiments have been performed on high and low sulphur Type 316 austenitic stainless steel specimens in simulated Pressurised Water Reactor primary coolant environments and evaluated via microstructural characterisation techniques to further the understanding of the mechanistic behaviour. At relatively high loading frequencies, the enhanced crack growth for both specimens appeared to be crystallographic and associated with slip localization. However, when the loading frequency was decreased, the crack growth rates for the low S specimen increased, whereas the high S specimen exhibited retarded crack growth and the crack path was no longer crystallographic.

Stability Analysis of Radial Turning Process for Superalloys

Abstract Stability detection in machining processes is an essential component for the design of efficient machining processes. Automatic methods are able to determine when instability is happening and prevent possible machine failures. In this work a variety of methods are proposed for detecting stability anomalies based on the measured forces in the radial turning process of superalloys. Two different methods are proposed to determine instabilities. Each one is tested on real data obtained in the machining of Waspalloy, Haynes 282 and Inconel 718. Experimental data, in both Conventional and High Pressure Coolant (HPC) environments, are set in four different states depending on materials grain size and Hardness (LGA, LGS, SGA and SGS). Results reveal that PCA method is useful for visualization of the process and detection of anomalies in online processes.

Study on heat transfer model of coolant boundary layer during high speed cutting process

In the high-speed cutting process, coolant is applied to ensure the cutting tools temperature stable. In the current study, scholars mainly studied the characteristics of the tool surface temperature during the cutting process. However, the cooling and heat transfer characteristics of the cooling fluid were ignored during the cutting process in their study. By analyzed the motion state of the coolant around the cutting tool, a heat transfer model of the coolant fluid is proposed in this paper based on the fluid boundary layer theory. In the heat transfer model, the solution of the temperature gradient of the coolant is obtained by solving the Brahzyus similarity solution. Moreover, the relationship between the temperature of the cutting tool in the coolant environment and the natural convection environment was analyzed by simulation experiment. Then the temperature trend of different Pr for coolant was obtained. In addition, the effect of coolant flow on the cooling effect of the system was discussed in this paper, and the expression of Nu number was obtained. The heat transfer model about the coolant boundary layer proposed in this paper is of great significance for the study of the coolant's cooling characteristics during high speed cutting.