Elemental distribution in a decommissioned high Ni and Mn reactor pressure vessel weld metal from a boiling water reactor

In this paper, weld metal from unique material of a decommissioned boiling water reactor pressure vessel is investigated. The reactor was in operation for 23 effective full power years. The elemental distribution of Ni, Mn, Si and Cu in the material is analysed using atom probe tomography. There are no well-defined clusters of these elements in the weld metal. However, some clustering tendencies of Ni was found, and these are interpreted as a high number density of small features. Cu atoms were found to statistically be closer to Ni atoms than in a fully random solid solution. The impact of the non-random elemental distribution on mechanical properties is judged to be limited

Integrated effect of thermal ageing and low flux irradiation on microstructural evolution of the ferrite of welded austenitic stainless steels

With the purpose to quantify microstructural changes with respect to ageing degradation, the microstructure of aged type 308 stainless steel welds with a ferrite content of 5-7% has been analysed using atom probe tomography. The weld metal of the core barrel of a decommissioned light water reactor, irradiated during operation of the reactor to 0.1 dpa, 1 dpa and 2 dpa at 280-285\ub0C (231,000 h), are compared to two similar thermally aged welds. In the ferrite of the irradiated welds, there is spinodal decomposition into Cr-rich α’ and Fe-rich α, with a similar degree of decomposition for all investigated doses, amplitudes of 21-26% and wavelengths between 6 and 9 nm. The ferrite of the thermally aged material showed evidence of decomposition when aged at 325\ub0C (an amplitude of 13-14% and wavelength of 5 nm), but not when aged at 291\ub0C, thus the irradiation significantly increases the rate of spinodal decomposition. There is G-phase (Ni Si Mn ) precipitation in the ferrite of all the weld metals except the one that was thermally aged at the lowest temperature. After irradiation to 1 and 2 dpa, the G-phase is considerably more well developed than after 0.1 dpa or thermal ageing

Analysis of thermal embrittlement of a low alloy steel weldment using fracture toughness and microstructural investigations

A thermally aged low alloy steel weld metal is investigated in terms of its fracture toughness and microstructural evolution and compared to a reference. The main purpose of the study is to investigate the effects of embrittlement due to thermal ageing on the brittle fracture toughness, and its effects on the influence of loss of crack tip constraint. The comparison of the investigated materials has been made at temperatures that give the same median fracture toughness of the high constraint specimens, ensuring comparability of the low constraint specimens. Ageing appears to enable brittle fracture initiation from grain boundaries besides initiation from second phase particles, making the fracture toughness distribution bimodal. Consequently, this appears to reduce the facture toughness of the low constraint specimens of the aged material as compared to the reference material. The microstructure is investigated at the nano scale using atom probe tomography where nanometer sized Ni-Mn-rich clusters, precipitated during ageing, are found primarily situated on dislocation lines

Mechanical behavior of high-Ni/high-Mn Barsebäck 2 reactor pressure vessel welds after 28 years of operation

To assess long-term operation of the reactor pressure vessel (RPV), surveillance programs are applied for periodic monitoring and prediction of the aging of the mechanical properties due to irradiation and thermal embrittlement. In literature, there are limited data sets to compare the results from the surveillance program to the aging of the RPV. In this work, the tensile and impact toughness properties of the high-Ni, high-Mn welds from decommissioned Barsebäck 2 RPV are characterized. The results indicate that the surveillance program describes sufficiently the aging of the RPV welds. Differences in mechanical properties of the welds from various regions are explained by variations in post-weld heat treatment. The synergetic effect of Ni and Mn on embrittlement appears not to result at low fluences in a significant difference in the embrittlement rate when compared to ASTM E900 embrittlement trend curve prediction

Study of Fusion Boundary Microstructure and Local Mismatch of SA508/Alloy 52 Dissimilar Metal Weld with Buttering

Funding Information: The authors wish to express their gratitude for the funding and support from Ringhals AB, OKG AB, Teollisuuden Voima Oyj and VTT Technical Research centre of Finland within the FEMMA (Forum for the Effect of Thermal Ageing and Microstructure on Mechanical and EAC Behavior of Ni-based Alloy Dissimilar Metal Welds) research project. The authors also thank NKS for funding the NKS-FEMMA (AFT/NKS-R(22)134/4) project. The authors would like to thank P. Arffman, J. Lydman, A. Nurmela and L. Sirkiä for the experimental contributions. The authors would like to thank U. Ehrnstén, B. Forssgren, H. Reinvall and H. Hänninen for suggestions and discussions. Publisher Copyright: © 2023 The Author(s)A SA508/Alloy 52 dissimilar metal weld (DMW) mock-up with double-sided Alloy 52 butterings, which is fully representative of Ringhals pressurizer surge nozzle DMW repair solution, was studied. The microstructure, crystal structure, elemental diffusion, carbide formation and macro-, micro- and nano-hardness of the SA508/nickel-base Alloy 52 buttering fusion boundary (FB) were investigated. Three types of FBs were analyzed, i.e., narrow FB (∼80–85% of whole FB), tempered martensitic transition region (∼15%) and wide partially mixed zone (∼1–2%). The different FB types were induced by the local heat flow and respective elementary diffusion, which significantly influence the local hardness mismatch across the DMW interface and the local brittle fracture behavior.Peer reviewe

Materials for Sustainable Nuclear Energy: A European Strategic Research and Innovation Agenda for All Reactor Generations

Nuclear energy is presently the single major low-carbon electricity source in Europe and is overall expected to maintain (perhaps eventually even increase) its current installed power from now to 2045. Long-term operation (LTO) is a reality in essentially all nuclear European countries, even when planning to phase out. New builds are planned. Moreover, several European countries, including non-nuclear or phasing out ones, have interests in next generation nuclear systems. In this framework, materials and material science play a crucial role towards safer, more efficient, more economical and overall more sustainable nuclear energy. This paper proposes a research agenda that combines modern digital technologies with materials science practices to pursue a change of paradigm that promotes innovation, equally serving the different nuclear energy interests and positions throughout Europe. This paper chooses to overview structural and fuel materials used in current generation reactors, as well as their wider spectrum for next generation reactors, summarising the relevant issues. Next, it describes the materials science approaches that are common to any nuclear materials (including classes that are not addressed here, such as concrete, polymers and functional materials), identifying for each of them a research agenda goal. It is concluded that among these goals are the development of structured materials qualification test-beds and materials acceleration platforms (MAPs) for materials that operate under harsh conditions. Another goal is the development of multi-parameter-based approaches for materials health monitoring based on different non-destructive examination and testing (NDE&T) techniques. Hybrid models that suitably combine physics-based and data-driven approaches for materials behaviour prediction can valuably support these developments, together with the creation and population of a centralised, “smart” database for nuclear materials

Deposition of Zr(C,N) Coatings by Chemical Vapour Deposition

In this master thesis the influence from process parameters within the Chemical vapour deposition process for a Zirconium Carbon-Nitride coating was investigated regarding growth rate, microstructure and texture. The interest in utilizing Zirconium Carbon-Nitride (Zr(C,N)) is due to its low coefficient of thermal expansion (CTE) relative the currently commonly used wear resistant coatings of Titanium-Carbon-Nitride (Ti(C,N)). The process parameters studied in this work is the ratio of the partial pressures of Zirconium tetrachloride over Acetonitrile (ZrCl4/CH3CN), addition of Nitrogen respectively hydrochloric acid, partial pressures of the precursors, reactor temperature and total gas flow. By controlling these process parameters one can control the grain size, growth rate within the reactor and texture of the Zr(C,N) coating deposited

Deposition of Zr(C,N) Coatings by Chemical Vapour Deposition

In this master thesis the influence from process parameters within the Chemical vapour deposition process for a Zirconium Carbon-Nitride coating was investigated regarding growth rate, microstructure and texture. The interest in utilizing Zirconium Carbon-Nitride (Zr(C,N)) is due to its low coefficient of thermal expansion (CTE) relative the currently commonly used wear resistant coatings of Titanium-Carbon-Nitride (Ti(C,N)). The process parameters studied in this work is the ratio of the partial pressures of Zirconium tetrachloride over Acetonitrile (ZrCl4/CH3CN), addition of Nitrogen respectively hydrochloric acid, partial pressures of the precursors, reactor temperature and total gas flow. By controlling these process parameters one can control the grain size, growth rate within the reactor and texture of the Zr(C,N) coating deposited

Wear testing of high-alloy carbon steel used in mining tools

Wear is a commonly occurring degradation mechanism for materials and components in the rock drilling industry. The wear can occur by either abrasion or adhesive wear. Further corrosion and presence of water or other lubricating fluids with or without particles may influence the behavior. Which mechanism, or mechanisms, and under which conditions it occurs, as well as the relative wear rate is dependent on the actual operating conditions for the component. In the present study, commonly available and general test methods for wear on high-alloy carbon steel has been analyzed. The project has been carried out through literature reviews and study visits at the tribology laboratory at KTH and at the Angstroms laboratory at Uppsala University. The present study indicates that it is difficult to suggest a feasible test method that is possible to use for all different situations of the wear that may occur. A test adapted to the actual situation is required to achieve a proper wear rate comparable to the wear rate in a real application.  According to the requirements from Ovako AB, a test that is general, cost effective and can be used when developing steel with higher wear-resistance, following wear testing methods has been compared: a pin-on-disk apparatus, a dry/wet sand/rubber wheel, a dry/wet sand/steel wheel, a tumbling mill, a particle erosion rig, a solid particle impingement using gas jets and a grinding machine. The tumbling mill, the grinder and the “Standard Test Method for Wear Testing with a Pin-On- Disk Apparatus” correspond to the requirements best. Ovako AB is recommended to continue the work with these testing methods. Nötning är en vanlig mekanism som orsakar nedbrytning på material i gruvindustrin. Nötningen kan förekomma som abrasiv eller adhesiv nötning. Korrosion och närvaro av vatten eller andra smörjande vätskor med eller utan lösa partiklar kan påverka beteendet. Den eller de mekanismer som styr nötningen såväl som nötningstalet beror på de aktuella förhållanden vilka materialet eller materialen verkar i. I denna studie har en generell testmetod för att utvärdera nötning på höglegerat kolstål har undersökts. Arbetet har genomförts genom litteratursökning samt studiebesök vid tribologiska laboratoriet på KTH samt på Ångströmska i Uppsala. Utifrån arbetet har det visat sig att det inte förekommer några generella nötningstest för alla applikationer, då det krävs ett test som är anpassat efter verkligheten för att få ut korrekt nötningstal. Utifrån Ovako ABs önskemål om ett generellt test som är ekonomiskt hållbart samt kan användas för att utveckla nötningsbeständigheten i de stål där nötning förekommer har följande testmetoder jämförts: pinne/skiva-maskin, blött/torrt sand/gummihjul, blött/torrt sand/stålhjul, roterande trumma, ”Erofugen”, partikelsprutare och en slipmaskin. De test som motsvarar kravprofilen bäst är den roterande trumman, slipmaskinen samt den standardiserade pinne/skiva-maskinen. Utifrån dessa testmetoder rekommenderas Ovako AB att fortsätta arbetet.