The cover depicts the chemical and physical complexity of the various species and interfaces within a molten salt reactor. To advance new approaches to molten salt technology development, it is necessary to understand and predict the chemical and physical properties of molten salts under extreme environments; understand their ability to coordinate fissile materials, fertile materials, and fission products; and understand their interfacial reactions with the reactor materials. Modern x-ray and neutron scattering tools and spectroscopy and electrochemical methods can be coupled with advanced computational modeling tools using high performance computing to provide new insights and predictive understanding of the structure, dynamics, and properties of molten salts over a broad range of length and time scales needed for phenomenological understanding. The actual image is a snapshot from an ab initio molecular dynamics simulation of graphene- organic electrolyte interactions. Image courtesy of Bobby G. Sumpter of ORNL. Molten Salt Chemistry Workshop Report for the US Department of Energy, Office of Nuclear Energy Workshop Molten Salt Chemistry Workshop Technology and Applied R&D Needs for Molten Salt Chemistry April 10–12, 2017 Oak Ridge National Laboratory Co-chairs: David F. Williams, Oak Ridge National Laboratory Phillip F. Britt, Oak Ridge National Laboratory Working Group Co-chairs Working Group 1: Physical Chemistry and Salt Properties Alexa Navrotsky, University of California–Davis Mark Williamson, Argonne National Laboratory Working Group 2: Analytical Chemistry Sam Bryan, Pacific Northwest National Laboratory Sheng Dai, Oak Ridge National Laboratory Working Group 3: Molten Salt Fission Product Chemistry and Solid Salt Radiolysis Bill DelCul, Oak Ridge National Laboratory Tina Nenoff, Sandia National Laboratories Working Group 4: Materials Compatibility James Keiser, Oak Ridge National Laboratory Preet Singh, Georgia Institute of Technology Working Group 5: Computational Chemistry and Materials Science Bobby Sumpter, Oak Ridge National Laboratory Brian Wirth, University of Tennessee–Knoxville Charles Henager, Pacific Northwest National Laboratory Office of Nuclear Energy Leads John Herczeg, Deputy Assistant Secretary for Nuclear Technology Research and Development, DOE-NE Stephen Kung, Program Manager, DOE-NE ORNL Creative Services and ORNL Research Library Deborah Counce, LeJean Hardin, Cindy Johnson, Kathy Jones, James Kidder This publication can be seen here: https://www.ornl.gov/content/molten-salt-chemistry-workshop Technology and Applied R&D Molten Salt Chemistry Workshop Table of Contents Abbreviations, Acronyms, and Initialisms ............................................................................................... v Executive Summary .................................................................................................................................. vii 1. Introduction ......................................................................................................................................... 1 1.1 Workshop Organization ................................................................................................................ 3 1.2 Future Research Directions ........................................................................................................... 3 References ............................................................................................................................................. 4 2. FRD 1: Understanding, Predicting, and Optimizing the Physical Properties of Molten Salts ...................................................................................................................................................... 5 2.1 Background and Current Status ..................................................................................................... 5 2.2 Technical Challenges and Research Directions ............................................................................ 7 2.2.1 Determining the Physical Properties of Molten Salts ....................................................... 7 2.2.2 Predicting the Chemical Speciation, Structure, and Dynamics of Molten Salts Solutions .............................................................................................................................. 15 References ........................................................................................................................................... 19 3. FRD 2: Understanding the Structure, Dynamics, and Chemical Properties of Molten Salts .................................................................................................................................................... 23 3.1 Background and Current Status ................................................................................................... 23 3.2 Technical Challenges and Research Directions .......................................................................... 28 3.2.1 Determining Molecular Structure by X-ray and Neutron Scattering and Spectroscopy ....................................................................................................................... 28 3.2.2 Correlating Electrochemistry and Spectroscopy for Online Monitoring and Predictive Modeling ............................................................................................................ 30 References ........................................................................................................................................... 33 4. FRD 3: Understanding Fission and Activation Product Chemistry and Radiation Chemistry .......................................................................................................................................... 37 4.1 Background and Current Status ................................................................................................... 37 4.2 Technical Challenges and Research Directions .......................................................................... 38 4.2.1 Understanding the Physical, Chemical, and Radiochemical Properties of the Fission and Activation Products in Molten Salts ................................................................. 38 4.2.2 Correlating Fission and Activation Product Behavior with Surrogates .......................... 40 4.2.3 Understanding the Physical and Chemical Impact of Short-lived Isotopes .................... 42 References ........................................................................................................................................... 43 5. FRD 4: Understanding Materials Compatibility and Interfacial Phenomena ............................ 45 5.1 Background and Current Status ................................................................................................... 45 5.2 Technical Challenges and Research Directions .......................................................................... 46 5.2.1 Advancing Spectroscopic and Scattering Investigation of MSR Interfaces.................... 46 Table of Contents iii Molten Salt Chemistry Workshop 5.2.2 Understanding Materials Compatibility in the Molten Salts Reactor Environment ........................................................................................................................ 47 5.2.3 Understanding Degradation Processes at the Material–Salt Interface ............................ 50 5.2.4 Understanding the Combined Effect of Chemistry and Radiation at the Interface ......... 51 5.2.5 Predicting Interfacial Interactions between Molten Salts and Structural Materials and/or Gases ........................................................................................................................ 53 References ........................................................................................................................................... 56 6. FRD 5: Guiding Next-Generation Materials for Molten Salt Reactors ....................................... 59 6.1 Background and Current Status ................................................................................................... 59 6.2 Technical Challenges and Research Directions .......................................................................... 59 6.2.1 Enabling Rapid Deployment of MSR Materials: Computational Challenges ................. 59 6.2.2 Guiding Experimental Exploration of Advanced “Super” Materials .............................. 63 6.2.3 Advancing Code Qualification of New Materials ........................................................... 64 References ........................................................................................................................................... 66 7. FRD 6: Creating a Virtual Reactor Simulation ............................................................................. 67 7.1 Background and Current Status ................................................................................................... 67 7.2 Technical Challenge and Research Directions ............................................................................ 67 7.2.1 Creating a Virtual Reactor Simulation ............................................................................ 67 References ........................................................................................................................................... 70 APPENDIX A: WORKSHOP RESOURCE DOCUMENT ................................................................ A-1 APPENDIX