Behavior of Metallic Materials Between 550 and 870°C in High-Temperature Gas-Cooled Reactor Helium Under Pressures of 2 and 50 bar

Cappelaere, M.; Perrot, Morgann; Sannier, J.

doi:10.13182/nt84-a33447

Cited by 19 publications

(12 citation statements)

References 3 publications

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“…Thus, it is important to consider additional factors associated with the HTGR steam generator environment that could accelerate the corrosion and associated failure rate of DMWs. Although information is available on the corrosion behavior of various base metal alloys in the HTGR environment 59,72,73,74,75,76 no reports are available in the open literature on the influence of gas impurities on creep-rupture properties of the DMWs. Lai and Wolwowicz 59 examined the effect of flowing helium on the creep rupture properties of 2.25Cr-1Mo steel and alloy 800H with the following impurities and concentration levels: 1500atm H 2 , 450μatm CO, 50μatm CH 4 , 50μatm H 2 O, and 5 μatm CO 2 .…”

Section: Effect Of Environment On Creep Rupture Propertiesmentioning

confidence: 99%

Review of Dissimilar Metal Welding for the NGNP Helical-Coil Steam Generator

DuPont¹

2010

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EXECUTIVE SUMMARYThe U.S. Department of Energy (DOE) is currently funding research and development of a new high-temperature gas-cooled reactor (HTGR) that is capable of providing high-temperature process heat for industry. The steam generator of the HTGR will consist of an evaporator-economizer section in the lower portion and a finishing superheater section in the upper portion. Alloy 800H is expected to be used for the superheater section, and 2.25Cr-1Mo steel is expected to be used for the evaporator-economizer section. Dissimilar metal welds (DMW) will be needed to join these two materials. It is well known that failure of DMWs can occur well below the expected creep life of either base metal and well below the design life of the plant. The failure time depends on a wide range of factors related to service conditions, welding parameters, and alloys involved in the DMW. The overall objective of this report is to review factors associated with premature failure of DMWs operating at elevated temperatures and identify methods for extending the life of the 2.25Cr-1Mo steel-to-alloy 800H welds required in the new HTGR. Information is provided on a variety of topics pertinent to DMW failures, including microstructural evolution, failure mechanisms, creep rupture properties, aging behavior, remaining-life estimation techniques, effect of environment on creep rupture properties, best practices, and research in progress to improve DMW performance.The microstructure of DMWs in the as-welded condition consists of a sharp chemical concentration gradient across the fusion line that separates the ferritic and austenitic alloys. Upon cooling from the weld thermal cycle, a band of martensite forms within this concentration gradient due to high hardenability and the relatively rapid cooling rates associated with welding. Upon aging, during post-weld heat treatment (PWHT), and/or during high-temperature service, C diffuses down the chemical potential gradient from the ferritic 2.25Cr-1Mo steel toward the austenitic alloy. This can lead to formation of a soft C denuded zone near the interface on the ferritic steel, and nucleation and growth of carbides on the austenitic side that are associated with very high hardness. These large differences in microstructure and hardness occur over very short distances across the fusion line (~ 50-100 m). A band of carbides also forms along the fusion line in the ferritic side of the joint. The difference in hardness across the fusion line increases with increasing aging time due to nucleation and growth of the interfacial carbides.Premature failure of DMWs is generally attributed to several primary factors, including: the sharp change in microstructure and mechanical properties across the fusion line, the large difference in coefficient of thermal expansion (CTE) between the ferritic and austenitic alloys, formation of interfacial carbides that lead to creep cavity formation, and preferential oxidation of the ferritic steel near the fusion line. In general, the large gradient in mechanical...

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Section: Effect Of Environment On Creep Rupture Propertiesmentioning

confidence: 99%

Review of Dissimilar Metal Welding for the NGNP Helical-Coil Steam Generator

DuPont¹

2010

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“…A significant body of corrosion information has been developed on several candidate alloys exposed to helium environments with a narrow range of impurity concentrations [Brenner and Nilsen 1978, Graham et al 1981, Johnson and Lai, 1981, Kondo 1981, McKee and Frank 1981, Bates 1984, Cappellaere et al 1984, Huchtemann 1989, and Graham 1990. The selected gas compositions were based predominantly on steam-cycle HTGRs, which were envisioned during the 1970s and 1980s.…”

Section: Corrosion Performance Datamentioning

confidence: 99%

“…Alloy containing 1 wt.% Y exhibited massive precipitation of Cr carbides and poor corrosion performance at 950°C. Cappellaere et al [1984] examined the influence of helium pressure on the corrosion of ferritic and austenitic materials by conducting tests at 2 atm in a circuit without helium recirculation and at 50 atm in the AIDA loop. The gas chemistries in both these experiments were the same (Table 3.8).…”

Section: Corrosion Performance Datamentioning

confidence: 99%

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Preliminary issues associated with the next generation nuclear plant intermediate heat exchanger design

Natesan

Moisseytsev

Majumdar

2009

Journal of Nuclear Materials

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Executive SummaryThe Next Generation Nuclear Plant (NGNP), which is an advanced high temperature gas reactor (HTGR) concept with emphasis on production of both electricity and hydrogen, involves helium as the coolant and a closed-cycle gas turbine for power generation with a core outlet/gas turbine inlet temperature of 900-1000*C. In the indirect cycle system, an intermediate heat exchanger is used to transfer the heat from primary helium from the core to the secondary fluid, which can be helium, nitrogen/helium mixture, or a molten salt. The system concept for the vary high temperature reactor (VHTR) can be a reactor based on the prismatic block of the GT-MHR developed by a consortium led by General Atomics in the U.S. or based on the PBMR design developed by ESKOM of South Africa and British Nuclear Fuels of U.K.This report has made a preliminary assessment on the issues pertaining to the intermediate heat exchanger (IHX) for the NGNP. Two IHX designs namely, shell and tube and compact heat exchangers were considered in the assessment. Printed circuit heat exchanger, among various compact heat exchanger (HX) designs, was selected for the analysis. Irrespective of the design, the material considerations for the construction of the HX are essentially similar, except may be in the fabrication of the units. As a result, we have reviewed in detail the available information on material property data relevant for the construction of HX and made a preliminary assessment of several relevant factors to make a judicious selection of the material for the IHX.The assessment included four primary candidate alloys namely, Alloy 617 (UNS N06617), Alloy 230 (UNS N06230), Alloy 800H (UNS N08810), and Alloy X (UNS N06002) for the IHX. Some of the factors addressed in this report are the tensile, creep, fatigue, creep fatigue, toughness properties for the candidate alloys, thermal aging effects on the mechanical properties, American Society of Mechanical Engineers (ASME) Code compliance information, and performance of the alloys in helium containing a wide range of impurity concentrations.A detailed thermal hydraulic analysis, using a model developed at ANL, was performed to calculate heat transfer, temperature distribution, and pressure drop inside both printed circuit and shell-and-tube heat exchangers. The analysis included evaluation of the role of key process parameters, geometrical factors in HX designs, and material properties. Calculations were performed for helium-to-helium, helium-to-helium/nitrogen, and helium-to-salt HXs. The IHX being a high temperature component, probably needs to be designed using ASME Code Section III, Subsection NH, assuming that the IHX will be classified as a class 1 component. With input from thermal hydraulic calculations performed at ANL, thermal conduction and stress analyses for both compact and shell-and-tube HXs were performed.Several conclusions were drawn from this assessment:• In general, majority of materials research and development programs in support of HTGRs were conducted in the...

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“…Another quasi-static test apparatus examined corrosion behavior of Hastelloy X, Alloy 800, and Inconel 617 in helium with 50 μatm of water, 450 μatm of CO at total pressures of 2 and 50 atm, and temperatures up to 870°C. 46 Although the experiments suggested that the kinetics of corrosion were increased at high pressure while the mechanism remained the same, the authors were doubtful that their chemistry measurement and control were sufficiently accurate to draw firm conclusions.…”

Section: Inl/ext-06-11494 Revision 0 June 2006mentioning

confidence: 99%

Kinetics of Gas Reactions and Environmental Degradation in NGNP Helium

Wright¹

2006

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A number of very high temperature helium-cooled reactors have been built and operated for extended periods. The helium coolant in the primary circuit has been found to contain low levels of impurities after steady-state operation that can lead to an environmental degradation of the high temperature alloys used for internals and heat exchangers. Depending on the impurity concentration and the temperature, high temperature alloys can undergo oxidation, carburization, or decarburization. The concentration of H 2 O and CC are of particular interest because they essentially control the oxygen partial pressure and carbon activity, respectively. The optimum coolant chemistry for long-term stability of high temperature alloys is slightly oxidizing and results in formation of a tenacious and protective Cr 2 O 3 scale.The most critical metallic component of the Next Generation Nuclear Plant (NGNP) is the heat exchanger. Inconel 617 is the primary candidate alloy for this application because of its superior creep resistance. The mechanisms of environmental interaction between this alloy and prototype Very High Temperature Reactor (VHTR) helium chemistries have been extensively studied. A modified type of Ellingham diagram that maps the ranges of carbon activity and oxygen partial pressure that result in each of the degradation mechanisms has been developed. In addition, at temperatures above about 950°C, additional degradation mechanisms arise that effectively determine the maximum temperature for sustained service. While the mechanisms of degradation are relatively well-known, the kinetics of the reactions for reactor conditions of high helium pressure and velocity are not well characterized.

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Behavior of Metallic Materials Between 550 and 870°C in High-Temperature Gas-Cooled Reactor Helium Under Pressures of 2 and 50 bar

Cited by 19 publications

References 3 publications

Review of Dissimilar Metal Welding for the NGNP Helical-Coil Steam Generator

Review of Dissimilar Metal Welding for the NGNP Helical-Coil Steam Generator

Preliminary issues associated with the next generation nuclear plant intermediate heat exchanger design

Kinetics of Gas Reactions and Environmental Degradation in NGNP Helium

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