1 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 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 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 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 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Liquid Metal Compatibility is Controlled by several mechanisms Dissolution –Numerous phenomena can affect mass transfer across metal-liquid interface, J=k (C 0 -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 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY There are two major contributors to dissolution mass transfer 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 J=k (C 0 -C)

5 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Eventually, Compatibility Issues Need To be Examined Under Dynamic,  T Conditions J i = k(C sol,i – C i )  Constant driving force for dissolution  Positive results from isothermal capsule experiments may not be reproduced under these conditions

6 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 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 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 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 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Chemical Analyses of the Pb-Li Revealed Little Reaction With SiC after 1000h Li (at.%) Si (ppma) C (ppma) O (ppma) N (ppma) Startn.d.<40< <40 800˚C 1000h 17.5%< °C 1000h 16.3%< ˚C 2000h 16.0%  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 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Specialized Capsule Experiments Have Been Used For SiC Exposures In Pb-17Li 800 and 1000˚C, 1000 h

10 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Negligible Change In Specimen Mass Before Or After Cleaning Was Observed

11 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 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 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Al-Containing (Al 2 O 3 -forming) Alloys Showed Significantly Reduced Mass Losses In Pb-17Li SpecimenCapsule Mass Change (mg/cm 2 ) 316 SS SSFe SSMo-3.8 ODS FeCrAlMo-0.2 Fe-28Al-2Cr+ZrMo-0.2 Ni-42.5AlMo-0.1 Capsule test: 1000 h, 700˚C, Pb-17Li 0.25  m *no preoxidation of specimens

13 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 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 J i = k(C sol,i – C i )

14 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Surface Morphology Of Exposed Stainless Steel Was Consistent With Dissolution 1  m 316SS in Mo Capsule, 1000 h, 700˚C, Pb-17Li

15 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Examination Of Cross Sections Confirmed Some Dissolution Had Occurred in Stainless Steel 10  m 2  m 1000 h, 700˚C, Pb-17Li

16 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Nickel Depletion Was Observed in Stainless Steel Counts Energy, ev Ni Counts Energy, ev 10  m 1000 h, 700˚C, Pb-17Li

17 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Aluminide-Formers Showed Little Mass Loss And Tended To From Stable, Protective Al-Rich Layers 2  m 1000 h, 700˚C, Pb-17Li ODS-FeCrAl in Mo Capsule Ni-42.5Al in Mo Capsule 2  m

18 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Fe Energy, ev Qualitative Analysis Indicated These Surface Layer Were Rich in Al and O (Likely Al 2 O 3 ) Al O Counts Energy, ev 1000 h, 700˚C, Pb-17Li ODS-FeCrAl in Mo Capsule Surface Layer Subsurface Alloy

19 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Example Cycle Efficiency as a Function of Interface FS/Pb- 17Li Temperature  For a fixed maximum neutron wall loading ~4.7 MW/m 2, -the max. η~38.8%, T max,FS <<550 o C for an interface FS/LiPb temperature of 475 o C; -the max. η~41.5%, T max,FS <<563 o C for an interface FS/LiPb temperature of 510 o C. T LiPb,out =700 o C;T max,FW =800 o C T ave,FW =700 o C; P pump /P thermal << 0.05