Showing papers by "Gary S. Was published in 2019"

Roadmap for the application of ion beam technologies to the challenges of nuclear energy technologies

Abstract: The use of ion beams to estimate materials performance for nuclear energy applications is advancing at a rapid rate with ion irradiations having been shown to produce radiation effects data of direct relevance for understanding neutron-induced displacement damage. Ion beam irradiation shows considerable promise for assisting in down selecting candidate materials for use in nuclear energy systems. Furthermore, ion beams allow rapid achievement of materials damage levels not accessible by neutron irradiation in test reactors due to cost and time constraints. Compared to test reactor irradiations, the relatively open configuration of ion beam irradiations allows capture of data on the effects of irradiation under very specific conditions of temperature, radiation dose, and radiation dose rate that are difficult or impossible to achieve otherwise. There are still multiple challenges to the deployment of ion beam data in support of reactor materials qualification arising from the lack of a detailed mechanistic understanding of potential difference between ion-induced and neutron induced materials damage. Recently, the Nuclear Science User Facilities presented a roadmap for the development and enhancement of current U.S. ion beam irradiation technologies within university and national laboratory settings, and especially for the deployment of new highly controlled in situ interrogation of materials during irradiation to provide dynamic and mechanistic data for model development. In this presentation, the status and capabilities of relevant U.S. ion beam facilities will be summarized and recommended “best practices” for performing ion irradiations will be described. The potential role of ion beam irradiations to assist the development and deployment of reactor materials will be outlined. Key objectives include developing methods for rapid and cost-effective materials selection and development, characterizing fundamental material response under irradiation, and developing a robust mechanistic understanding of microstructure evolution under irradiation (including development and validation of reliable predictive models for microstructure evolution).

Atomistic simulation of the obstacle strengths of radiation-induced defects in an Fe–Ni–Cr austenitic stainless steel

Abstract: A molecular dynamics method is employed to simulate the interaction of an edge dislocation with a combined solute cluster-dislocation loop defect, as well as independent faulted interstitial dislocation loops and solute clusters in an Fe–12Ni–20Cr at a temperature of 300 K. The examined defects are typical radiation-induced defects in austenitic stainless steels used as core structural components in nuclear reactors, while the selected composition matches with commercial grade 304L alloy. The dislocation-defect interaction is examined, and the peak shear stress required to overcome the obstacle array, and its dependence on obstacle size, solute concentration, and orientation is determined. The peak shear stress is then converted to an effective obstacle strength (α). Results show that dislocation loops are stronger obstacles than solute clusters, and their strength is heavily dependent on orientation, while the strength of solute clusters is largely dependent on the solute concentration. The total strength of the combined solute cluster-dislocation loop defect is largely contributed by the dislocation loop, though a fraction of the cluster strength is added as well.

Austenitic Stainless Steels

Abstract: Austenitic stainless steels are one of the most important alloy systems used as structural components in current and future nuclear reactor systems. This chapter reviews the physical and mechanical behavior of stainless steels in the reactor environment. Radiation-induced metallurgical changes include radiation-induced segregation, dislocation loop formation, phase stability, and transmutation. Radiation-induced mechanical property changes reviewed include hardening, fracture toughness, embrittlement, swelling, creep, and fatigue. The interaction of stainless steel with the environment is also important and fuel-clad chemical interaction in fast reactors is covered, along with chemical compatibility with the water coolant in light water reactors. Degradation modes include stress-corrosion cracking, irradiation-assisted stress-corrosion cracking, and irradiation-accelerated corrosion. Stainless steels are likely to continue to be important in light water reactors with life extension as well as small modular reactors and many Generation IV (GenIV) reactor systems.

Corrosion Issues in Current and Next-Generation Nuclear Reactors

Abstract: Corrosion of structural components in nuclear power plants is a major issue impacting plant capacity factor and operational costs, and it will continue to grow in importance both in light-water reactors (LWRs) receiving life extensions and in next-generation systems. This chapter reviews the corrosion processes, mechanisms, and consequences of the coolants currently in use and expected in GenIV reactors. These include LWR coolants; primary and secondary water systems in pressurized water reactors, and normal and hydrogen water chemistries in boiling water reactors, as well as supercritical water in the supercritical water reactor. Corrosion, carburization, and decarburization due to impurities in high-temperature helium are covered as well as corrosion in molten salt and liquid metals including sodium and lead alloys. Together, these coolants cover the majority of current and next-generation environments in which structural materials must function.

Creation of a remotely monitored and controlled ion beam laboratory using novel hardware and software tools

Abstract: The Michigan Ion Beam Laboratory (MIBL) at the University of Michigan houses three electrostatic accelerators and six ion sources, providing beams to five target chambers and a TEM via nine distinct beamlines. Such a large system incorporates numerous control and monitoring instruments that can more easily be managed through a digital remote interface system. MIBL has implemented a variety of standard laboratory hardware and custom alternative hardware and software tools into a remote interface system that provides for greater laboratory efficiency, increased application flexibility and information flow and reduced cost. The outcome is that users can operate three accelerators and their corresponding beamline system from one console using a master control program, eliminating the need to constantly traverse the facility to monitor and manipulate instruments. Furthermore, the digitalization and centralization of the data generated by each subsystem has allowed for logging and variable correlation that would otherwise be impossible at such a large scale, and enabled the future application of modern tools such as machine learning to enhance operational efficiency.