Comments on Corrosion R&D Needs for DCLL

1. Comments on Corrosion R&D Needs for DCLL B.A. Pint and P.F. Tortorelli Presented by S.J. Zinkle Oak Ridge National Laboratory US ITER-TBM Meeting Idaho Falls, ID August 10-12, 2005

2. Compatibility in the DCLL system will likely involve multiple materials • In-vessel TBM • ferritic/martensitic steel, SiC FCI • External piping • Ni-base superalloy? • Tritium processing • Refractory alloy??, tritium permeation barrier materials?? • Heat exchanger • Material options??

3. Liquid Metal Compatibility is Controlled by several mechanisms • Dissolution • Numerous phenomena can affect mass transfer across metal-liquid interface, J=k (C0-C) • Laminar vs. turbulent flow (including magnetic field effects) • Solubility temperature dependence • Impurity and interstitial transfer • Very important for refractory metals (and BCC metals in general) • Alloying between the liquid metal and solid • Typically eliminated early on in selection process (showstopper) • Compound reduction • Often most relevant for ceramics (e.g., SiC insert) • The last three mechanisms can be roughly evaluated using low-cost capsule experiments; the 1st mechanism requires flowing loop tests

4. There are two major contributors to dissolution mass transfer J=k (C0-C) • Static isothermal mechanisms • Capsule tests can provide initial data on solubilities (infinite dilution steady-state approximation) • Flowing, nonisothermal mechanisms • Rate-controlling steps include surface reaction, liquid-phase diffusion through boundary layer, and solid state diffusion

5. Eventually, Compatibility Issues Need To be Examined Under Dynamic, DT Conditions Ji = k(Csol,i – Ci) • Constant driving force for dissolution • Positive results from isothermal capsule experiments may not be reproduced under these conditions

6. Current knowledge of candidate materials for DCLL system is largely limited to static capsule tests • Substantial experimental database on ferritic steel compatibility with flowing Pb-Li • Comprehensive analysis of existing data is needed • Database for other materials generally does not include information for nonisothermal flowing systems and effects of magnetic fields • Very little is known about potential stress corrosion cracking mechanisms

7. Concluding remarks • Need to establish reference design (materials, operating conditions) asap • Near-term compatibility R&D activities would focus on analysis of existing compatibility for ferritic/martensitic steel with flowing Pb-Li • Also continue limited number of static capsule tests on candidate piping materials (possibility to avoid coatings or ceramic inserts) • Medium-term activities would be centered on flowing loop experiments • Thermal convection loop • Other loops? • Scoping experiments on stress-corrosion cracking should also be initiated in the near- to medium-term

8. Chemical Analyses of the Pb-Li Revealed Little Reaction With SiC after 1000h • No significant mass gains after any capsule test • Si detected after 2,000h at 1100°C, still less than Kleykamp • PbLi not analyzed yet for 5,000h 800°C or 1,000h 1200°C

9. Specialized Capsule Experiments Have Been Used For SiC Exposures In Pb-17Li 800 and 1000˚C, 1000 h

10. Negligible Change In Specimen Mass Before Or After Cleaning Was Observed

11. Corrosion-Resistant Metallic Coatings for Pb-17Li • At highest temperatures at and near first wall, SiC flow channel inserts can provide protection • Ducting behind this more likely to be made of conventional steels • Pb-17Li is quite corrosive toward certain ferrous and Ni-based alloys at temperatures above 450°C • One possible solution to ducting protection is corrosion-resistant aluminized coatings on strong conventional alloys: aluminide surface layers should be stable in Pb-17Li (Hubberstey et al., Glasbrenner et al.)

12. Al-Containing (Al2O3-forming) Alloys Showed Significantly Reduced Mass Losses In Pb-17Li Capsule test: 1000 h, 700˚C, Pb-17Li 0.25 m *no preoxidation of specimens

13. 316 SS Results Can Be Understood Based On Fundamental Dissolution Driving Force • Dissolution continues until saturation is reached • For specimens of 316 SS, saturation is reached sooner in a 316 SS capsule because both are contributing solute (mainly Ni) • Fe or Mo capsules are relatively inert Ji = k(Csol,i – Ci)

14. Surface Morphology Of Exposed Stainless SteelWas Consistent With Dissolution 1 mm 316SS in Mo Capsule, 1000 h, 700˚C, Pb-17Li

15. Examination Of Cross Sections ConfirmedSome Dissolution Had Occurred in Stainless Steel 10 mm 2 mm 1000 h, 700˚C, Pb-17Li

16. Nickel Depletion Was Observed in Stainless Steel Counts Counts Energy, ev Energy, ev 10 mm Ni 1000 h, 700˚C, Pb-17Li

17. Aluminide-Formers Showed Little Mass Loss And Tended To From Stable, Protective Al-Rich Layers 2 mm 2 mm 1000 h, 700˚C, Pb-17Li Ni-42.5Alin Mo Capsule ODS-FeCrAlin Mo Capsule

18. Qualitative Analysis Indicated These Surface Layer Were Rich in Al and O (Likely Al2O3) Al Counts O Fe Energy, ev Energy, ev Surface Layer Subsurface Alloy ODS-FeCrAl in Mo Capsule 1000 h, 700˚C, Pb-17Li

19. Example Cycle Efficiency as a Function of Interface FS/Pb-17Li Temperature TLiPb,out=700oC;Tmax,FW=800oC Tave,FW=700oC; Ppump/Pthermal << 0.05 • For a fixed maximum neutron wall loading ~4.7 MW/m2, -the max. η~38.8%, Tmax,FS<<550oC for an interface FS/LiPb temperature of 475 oC; -the max. η~41.5%, Tmax,FS<<563oC for an interface FS/LiPb temperature of 510 oC.