Comments on Top-level Issues for Proposed ITER Molten Salt Test. Blanket Modules. UCLA, February 23-25, ITER TBM Project Meeting. S.J.

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1 Comments on Top-level Issues for Proposed ITER Molten Salt Test Blanket Modules S.J. Zinkle Metals and Ceramics Division Oak Ridge National Laboratory ITER TBM Project Meeting UCLA, February 23-25, 2004

2 Overview of key issues Physical properties of coolant Freeze-thaw issues (molten salt expansion behavior is different from metals) Chemical compatibility with surrounding materials Redox: appropriate buffers for TF, F - control Radiolysis effects (F- formation) for concepts that involve solid Flibe Tritium barriers Is tritium permeation allowed within high flux regions of TBM Demonstration of MS tritium recovery technology Recapture technical expertise for processing and handling large quantities of molten salt

3 Summary of some physical property data for candidate molten salts COMPARISON OF THE THERMAL CONDUCTIVITY OF LIQUID COOLANTS COMPARISON OF THE SPECIFIC HEAT OF LIQUID COOLANTS (Ohse1985) (Schulz 1991) (F) 2 BeF 2 (Cantor 1968) Thermal Conductivity (W/m-K) (F) 2 BeF (Ohse 1985) (Schulz 1991) (F) 2 BeF 2 (Cantor 1968) COMPARISON OF THE ELECTRICAL RESISTIVITY OF LIQUID COOLANTS (F) 2 BeF 2 (F) BeF 2 (Ohse, 1985) (Schulz, 1991) (F) BeF 2 (Janz, 1988) (F) 2 BeF 2 (Janz, 1988) Electrical Resistivity (Ω-m) Specific Heat (J/kg-K) (F) 2 BeF 2 COMPARISON OF THE SURFACE TENSION OF LIQUID COOLANTS (Ohse1985) (Schins 1967, Buxbaum 1984) (F) BeF 2 (Janz 1988) (F) 2 BeF 2 (Janz 1988) Surface Tension (N/m) (F)2 BeF 2 (F) BeF

4 Summary of some physical property data for candidate molten salts Physical property data for Flinabe are not available (melting temperature measurements for promising compositions in progress) Physical property data for Flibe only available over limited temperature range COMPARISON OF THE DYNAMIC VISCOSITY OF LIQUID COOLANTS (F) BeF 2 (F) 2 BeF 2 (Ohse1985) (Schulz 1991) (F) BeF 2 (Janz 1988) (F) 2 BeF 2 (Janz 1988) Dynamic Viscosity (Pa-s)

5 Chemical compatibility: Structural material interface temperature limits with molten salts Published experimental compatibility data are not available for candidate molten salts and structural materials* APEX program assumed an upper temperature limit of 700 C for ferritic steel and Flibe due to corrosion considerations Based on studies for 304 and 316 austenitic stainless steel performed at 650 C with carefully controlled redox chemistry From chemistry viewpoint, corrosion of many materials in Flibe is controlled by impurities Redox control is critical for corrosion control Ni-based alloys have better compatibility than Fe base alloys Interface limits also need to be obtained for nonstructural materials *S.J. Zinkle and N.M. Ghoniem, Fus. Eng. Des (2000) 55

6 Chemical compatibility: Structural material interface temperature limits for Flibe (similar interface limits need to be compiled for nonstructural materials) Estimated Operating Temperature mits for Structural Alloys in Fusion Reactors: Flibe Coolant W Mo (TZM) Ta-8W-2Hf Nb-1Zr-.1C V-4Cr-4Ti ODS ferritic st. F/M steel 316 SS SiC/SiC Temperature ( C) () () (F) 2 (BeF 2 ) Tmelt=470 C The question marks indicate uncertainties in the upper operating temperature limit due to lack of data on chemical compatibility with Flibe. S.J. Zinkle and N.M. Ghoniem, Fus. Eng. Des (2000) 55

7 Personal comment Some innovative solutions have been identified to resolve many of the key technical issues for molten salt TBMs Dual cooled concept Flinabe instead of Flibe Tritium recovery systems but very substantial effort is required to validate their behavior Given realistic budget projections for ITER TBM R&D in the US (and including collaborative work by international partners), is it feasible to develop key MS TBM technologies within ~10 year period

8 Summary of key issues Physical properties of coolant Requires several years of significant effort Freeze-thaw issues (molten salt expansion behavior is different from metals) Was >1 year up-front analysis effort for dismantling of MSRE Chemical compatibility with surrounding materials Redox: appropriate buffers for TF, F - control Radiolysis effects (F- formation) for concepts that involve solid Flibe Tritium barriers Is tritium permeation allowed within high flux regions of TBM Demonstration of MS tritium recovery technology Some promising candidates have been identified, but very substantial effort is required to validate their behavior Recapture technical expertise for processing and handling large quantities of molten salt Move from beakers to vats.