Presented by: Dr Fabio CISMONDI Karlsruher Institut für Technologie (KIT)

1. Recent design developments in the EU HCPB TBM F. Cismondi1, S. Kecskes1, B. Kiss2, F. Hernandez1, L.V. Boccaccini1 1Karlsruhe Institute of Technology, Germany, 3Budapest University of Technology and Economic, Hungary Presented by: Dr Fabio CISMONDI Karlsruher Institut für Technologie (KIT) Institut für Neutronenphysik und Reaktortechnik e-mail: fabio.cismondi@kit.edu

2. Contest of the study • Helium Cooled Pebble Beds (HCPB) and Helium Cooled Lithium Lead (HCLL) Test Blanket Modules (TBMs) are the two DEMO blankets concepts selected by EU to be tested in ITER. • The Test Blanket Systems (TBS) are developed by different Associations throughout EU. • The European Joint Undertaking “Fusion for Energy” is in charge of delivering the Test Blanket Modules System (TBS) to ITER. • The European partners developing the TBS are joint together into a Consortium Agreement (TBM-CA). • The TBM CA works under contracts with F4E • KIT and CEA develop within TBM CA the design of the HCLL and HCPB TBMs.

3. Contest of the study • TBM test programme main objectives in ITER • Demonstrate tritium breeding capability and verify on-line tritium recovery and control systems; • Ensure high grade heat production and removal; • Demonstrate the integral performance of the blanket systems in a fusion relevant environment; • Validate and calibrate design tools and database used in the blanket design process. • DEMO relevancy for the TBMs: • Maximum geometrical similarity between the design of the TBM and the corresponding DEMO blanket modules; • Active cooling of the structure by Helium at 8 MPa with 300°C/500°C inlet/outlet temperatures, • Same structural materials; • Maximum structural temperature limited to 550°C; • Same manufacturing and assembly techniques. • Same functional materials and relevant Be and OSI temperatures. Structural material HCPB and HCLL TBMs structural material is the Reduced Activation Ferritic-Martensitic (RAFM) steel EUROFER97. RAFM steels derive from the conventional modified 9Cr-1Mo steel eliminating the high activation elements (Mo, Nb, Ni, Cu and N). Main advantages:excellent dimensional stability (low creep and swelling) under neutron irradiation. Drawback:ductility characteristics considerably lower than austenitic steels and severely reduced following irradiation.

4. 710mm First Wall Vertical SGs Manifold plates Back plate 1660mm Plasma side Breeder Units By pass He outlet He inlet Caps Purge gas in/outlet Horizontal SGs HCPB TBM design description • 1660 mm (poloidal) × 484 mm (toroidal) × 710 mm (radial) • Robust box (First Wall and Caps) • Internal structure of Stiffening Grids (SGs) • 5 backplates (BP) constitute the coolant manifolds • Horizontal SGs crossing the TBM box to ensure the box stiffness • Breeder Units (BUs): • Arranged in the space defined by the SGs. • Filled by ceramic breeder pebbles (Li4SiO4) and Beryllium neutron multiplier pebbles • Based on U-shaped Cooling Plates (CPs) extracting the heat • Helium at 80bar cools the TBM box components and the BUs CPs. • Helium at 4bar purges the Breeder Zone for tritium removal 3 | Recent developments in the design of the EU HCPB-TBM, Fabio Cismondi

5. Design development strategy • FW: larger bending radius (150mm) in HCPB TBM • Objective: develop a design of the TBM boxes maximizing the similarities. • Strategy: synergies are maximized but differences are kept in the most critical points to investigate different design options and minimize the risk. • Critical points: • FW, fabrication issues • Manifold, design different for the different internal engineering of the 2 TBMs Manifolds: Horizontal SGs crossing the TBM box (HCPB), Stiffening rods (HCLL)

6. Detailed view of BU design MF.2 MF.3 MF.1 Back plate Radial-poloidal cut and BU detail Li4SiO4 Be MF.4 He at 8 MPa, T 300 to 500 °C Purge gas MFs

7. PLASMA Detailed view of BU design MF.2 MF.3 MF.1 First Wall Back plate Be pebble bed He coolant Li pebble bed Be pebble bed He purge gas n 14,08 MeV Li pebble bed Be pebble bed He coolant Cooling/stiffening grid MF.4 Purge gas MFs

8. Start HCPB TBM design life cycle Structural concept Material selection Neutronic Nuclear heating rate Tritium breeding Ratio Support concept, manteinance Fabricability Thermal-hydraulics Tritium recovery Temperature of structural, functional materials Coolant velocity and pressure loss Thermo-mechanics Stress evaluation Overall performance evaluation End

9. 3D CFD model of the TBM box Temperature distribution at t1=40s. Primary + secondary stress field on the TBM at t2=500s • Design Description Document (DDD) of the TBM box released (complete set of Build To Print CAD drawings performed) MPa 0 120 240 360 450 • Improved modeling of pebble beds region: • thermal conductivity temperature and strain (for Be) dependent • thermal contact resistance temperature dependent.

10. 3D CFD model of the BU Goal: determine helium coolant mass flow rate in the different subcomponents and heat fluxes generated in BU and deposed on the subcomponents. First Wall Breeder Unit CFD model • Improved modeling of pebble beds region: • thermal conductivity temperature and strain (for Be) dependent • thermal contact resistance temperature dependent. Horizontal SGs Vertical SGs Cooling Plates Thermal contact resistance between pebble beds and structural material: correlations from Yagi & Kuniused to define the HTC between pebble beds and structural material: • Improved modeling of pebble beds region: • thermal conductivity temperature and strain (for Be) dependent • thermal contact resistance temperature dependent.

11. z x 3D CFD model of the BU Structural analyses: secondary stresses and structural deformation ∆x ≈ - 0,31mm ∆x ≈ - 0,5mm ∆sbed ≈ 0,4mm ∆x ≈ + 0,09mm ∆x ≈ + 0,17mm y ∆y ≈ + 2,09mm ∆y ≈ + 1,96mm • Improved modeling of pebble beds region: • thermal conductivity temperature and strain (for Be) dependent • thermal contact resistance temperature dependent.

12. 3D CFD model of the BU Beryllium: k as a function of the temperature T and the pebble bed strain ε: values of ε=0.2%, 0,32% and 0,5% (corresponding respectively to a pressure of 2.0, 1.0 and 0.5MPa) have been considered as being characteristic for the three zones OSI: variation of the OSi thermal conductivity with the temperature : The OSi thermal conductivity has the same order of magnitude than the purge gas one and its variation with the temperature is limited. • Improved modeling of pebble beds region: • thermal conductivity temperature and strain (for Be) dependent • thermal contact resistance temperature dependent.

13. 3D CFD model of the BU • Transient analyses performed (typical ITER pulse). • Maximal temperatures: • Low strain region in Be 760˚C. • OSi pebbles 870˚C. • Helium outlet stable at 490˚C by the end of the pulse. • Improved modeling of pebble beds region: • thermal conductivity temperature and strain (for Be) dependent • thermal contact resistance temperature dependent.

14. 3D CFD model of the BU • Transient analyses performed (typical ITER pulse). • Maximal temperatures: • Low strain region in Be 760˚C. • OSi pebbles 870˚C. • Helium outlet stable at 490˚C by the end of the pulse. • Improved modeling of pebble beds region: • thermal conductivity temperature and strain (for Be) dependent • thermal contact resistance temperature dependent.

15. 3D CFD model of the BU Transient analyses performed (typical ITER pulse). Temperatures in Be and OSI at the end of the plasma pulse First Wall Breeder Unit CFD model Horizontal SGs Vertical SGs Cooling Plates

16. Transient thermo mechanical analyses of the BU Goal: Evaluate thermo-mechanical performance of the BU. Design changes implemented to fulfill the design criteria. The selected design C&S is RCC-MR 2007 completed by SDC-IC ITER rules (adressing irradiation damages). SM2 SM1 Primary stress in base design. Equivalent Von Mises

17. Transient thermo mechanical analyses of the BU Submodel 2: BU manifold center region BU base design Design improvement: 20mm thick BU backplate and stiffeners

18. Transient thermo mechanical analyses of the BU • M-Tpe damages assessment 3 10 9 4

19. Transient thermo mechanical analyses of the BU • M-Tipe damages assessment • C-Tipe damage assessment 3 10 4

20. Progress in fabrication • 4x Cooling plates (CPs) • 2x U-shaped CPs • 4x Lateral Wraps • 2x U-shaped Lateral Wraps • 1 BU Backplate • 1x Inlet + 1x Outlet pipes • 2x Ditributor Frontplate • 2x Distributor Backplate • 2x Grill plate • Complexity of the BU manufacturing is mainly in the CPs: manufacturing test mock-ups are addressed to study the CPs fabrication techniques. • Complex mounting sequence: TIG orbital welding adressed.

21. Progress in fabrication • Complete set of Build To Print CAD drawings performed and Design Description Document (DDD) of the BU released :

22. Slightbump, poortorchorientation Progress in fabrication • Manufacturing of CP mock-ups • Qualification of TIG orbital welding Qualification in welding laboratories of CEA Saclay to obtain welding parameters for BU TIG2 (purge gas pipe with backplate manifold, RCC-MR and ISO starndards) • Qualification of fabrication techniques • BU bending radius (Uni Stuttgart) • Cooling channels with Spark Erosion (industry)

23. BU mock-up testing program in EU • BU container, optimal shape for: • the interface with Heblo facility • leak tightness • instrumentation • access to the testing zone • experimental plan flexibility • Goal: Design and Procurement of a BU Mock-up Instrumentation access from the mock up side: high testing possibilities and flexibility Possible access for the instrumentation from the back side BU cell, 1 to 1 BU dimensions

24. TBM design requirements • Several functional requirements for the HCPB Blanket are related to the Solid Breeder performances. They concern: • Neutronic performances for T self-sufficiency (TBR, Tritium Breeding Ratio); • Temperature control; • Long Blanket lifetime; • Tritium extraction; • Material compatibility; • Low tritium inventory in materials; • Low activation (for waste management and recycling). • Most of these requirements have been quantified for the design of DEMO and FPP, e.g. a calculated TBR not lower than 1.12 is requested for DEMO and FPP or a blanket lifetime compatible with a neutron fluence of ~15 MWa/m2 is assumed in the FPP. • These requirements are the basis on which sets of specification for the pebble production have been generated. • The connection among these general functional requirements and specification of the pebble (e.g. density, Li-6 enrichment, etc.) and pebble beds (e.g. effective thermal conductivity, packing factor, etc.) can be reconstructed for some of them, but can be very complicated in other case. • E.g. the nuclear analyses can correlate well properties like material density, pebble bed packing, ceramic composition with the TBR, allowing to determine the required properties for the pebble production. More complicated is to state the impact that e.g. the crash load value has on functional requirements like the T extraction or lifetime; fragmentation of pebble (that can impact the purging functionality) should be minimised, but a quantification of an upper limit necessitate further R&D. • Then ITER TBM has specific functional requirement. The specifications of the pebbles for TBM are oriented to the specification generated for DEMO/FPP. I.e. in TBM relevant reactor pebble beds will be tested trying to reproduce the most relevant reactor conditions. Deviations are introduced to cope with specific ITER relevant requirement; e.g. Li-6 enrichment in the ceramic is used at the “maximum” enrichment level of 90 in order to compensate the lower T and heat production related to lower neutron wall load in ITER (0.78 vs. 2.5 MW/m2 in a FPP).

25. Conclusions • Main results achieved: • Definition of C&S for TBM design and analyses • Definition and analyses of main TBM specific loading conditions • Transient thermo mechanical analyses of a standard ITER pulse. • Release of DDD for TBM box and Bus. • Important outcomes of the TBM transient analyses: • Several junctions present peak stresses : design optimization is on-going. • Open issues: • Design rules developed mainly for austenitic-type steels (i.e. 316L(N)-IG ITER shielding steel) • Limited experience with martensitic-type steel in a fusion relevant environment, • Concerns regarding the validity/degree of conservatism of the C&S rules when taking into account Eurofer97 mechanical properties. • Next priorities: • Develop dedicated models and studies addressing design issues • Assess possible requirements and operating scenarios limiting the margins under which the design can evolve. • Experiments validating FE modeling: pebble beds thermo mechanics, fluid dynamic, structural material behavior