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

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. 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. The TBM-CA groups six Associates: CEA, CIEMAT, ENEA, FZK, NRI and RMKI. The TBM-CA is a strategic and organisational cooperation among associates to determine the rules they agree to apply in order to make proposals for and to implement contracts with the domestic agency to develop, produce, qualify, install and operate the EU TBM Systems in ITER. 1 | Recent developments in the design of the EU HCPB –TBM, Fabio Cismondi

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. Test objectives in ITER: The TBM test programme in ITER has, as main objectives: demonstrate tritium breeding capability and verify on-line tritium recovery and control systems to ultimately enable the extrapolation to a full size blanket; ensure high grade heat production and removal to demonstrate the feasibility of electricity production; validate and calibrate the design tools and the database used in the blanket design process including neutronics, electromagnetics, heat transfer and hydraulics; demonstrate the integral performance of the blanket systems in a fusion relevant environment. DEMO relevancy In order to fulfill the test objectives, the HCLL-TBM shall insure maximum resemblance to the corresponding DEMO blanket (DEMO relevancy). The issue of DEMO relevancy and how to achieve it in the TBM testing programme has extensively been discussed in. Methods to quantify the DEMO relevancy of the TBM design have been proposed in DEMO relevancy for the TBMS From a design point of view, the requirement of DEMO relevancy imposes the following constraints: maximum geometrical similarity between the design of the TBM and the corresponding DEMO blanket modules; an active cooling of the structure by circulating 8 MPa Helium with 300°C/500°C inlet/outlet temperatures, the maximum structure temperature being limited to 550°C; same structural materials; same manufacturing and assembly techniques. Moreover, the TBM being an ITER component, it must comply with the general requirements defined by Structural material The HCPB and HCLL TBMs structural material is Eurofer97 Reduced Activation Ferritic-Martensitic (RAFM) steel. RAFM steels are derived from the conventional modified 9Cr-1Mo steel, but with the high activation elements (Mo, Nb, Ni, Cu and N) eliminated. main advantages excellent dimensional stability (low creep and swelling) under neutron irradiation. Drawback: ductility characteristics are considerably lower than austenitic steels and furthermore severely reduced following irradiation. 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. 2 | Recent developments in the design of the EU HCPB-TBM, Fabio Cismondi

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 First Wall Vertical SGs Breeder Units Horizontal Caps Plasma side 1660mm 710mm Manifold plates Back plate He outlet He inlet Purge gas in/outlet By pass Helium at 80bar cools the TBM box components and the BUs CPs. Helium at 4bar purges the Breeder Zone for tritium removal 1660 mm (poloidal) × 484 mm (toroidal) × 710 mm (radial) steel box robust box (First Wall and Caps) reinforced by an internal structure of Stiffening Grids (SGs). The Breeder Units (BUs) are arranged in a modular array in the space defined by the SGs. BUs based on Cooling Plates (CPs) extracting the heat from the breeder material: two U-shaped CPs are supported by the BU back plate and are filled with ceramic breeder pebbles (Li4SiO4). The Beryllium pebbles (neutron multiplier) fills the space between the canister outside surface and the SGs. Helium at 80bar is cooling the TBM box components and the BUs CPs. For tritium removal a purge gas circuit is incorporated into the BUs The structural material is the RAFM steel EUROFER 3 | Recent developments in the design of the EU HCPB-TBM, Fabio Cismondi

Design development strategy FW: larger bending radius (150mm) in HCPB TBM Manifolds: Horizontal SGs crossing the TBM box (HCPB), Stiffening rods (HCLL) 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 Design development strategy Requirement: develop a design of the TBM boxes maximizing the similarities. Ideal final goal: the 2 TBM boxes are identical Strategy: synergies are maximized but differences have been kept in the most critical points to investigate two different design options Critical points: FW, fabrication issues Manifold, design different for the different internal engineering of the 2 TBMs 4 | Recent developments in the design of the EU HCPB-TBM, Fabio Cismondi

Detailed view of BU design Purge gas MFs Back plate MF.1 MF.4 MF.3 MF.2 Radial-poloidal cut and BU detail Li4SiO4 Be He at 8 MPa, T 300 to 500 °C 5 | Recent developments in the design of the EU HCPB-TBM, Fabio Cismondi

Detailed view of BU design Purge gas MFs Back plate MF.1 MF.4 MF.3 MF.2 Be pebble bed Li pebble bed PLASMA First Wall n 14,08 MeV Cooling/stiffening grid He coolant He purge gas 6 | Recent developments in the design of the EU HCPB-TBM, Fabio Cismondi

HCPB TBM design life cycle Start Structural concept Material selection Neutronic Tritium breeding Ratio Nuclear heating rate Thermal-hydraulics Temperature of structural, functional materials Coolant velocity and pressure loss Thermo-mechanics Stress evaluation Overall performance evaluation End Tritium recovery Fabricability Support concept, manteinance 7 | Recent developments in the design of the EU HCPB-TBM, Fabio Cismondi

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 8 | Recent developments in the design of the EU HCPB-TBM, Fabio Cismondi Improved modeling of pebble beds region: thermal conductivity temperature and strain (for Be) dependent thermal contact resistance temperature dependent.

Improved modeling of pebble beds region: 3D CFD model of the BU First Wall Vertical SGs Breeder Unit CFD model Horizontal SGs Cooling Plates Goal: determine helium coolant mass flow rate in the different subcomponents and heat fluxes generated in BU and deposed on the subcomponents. Improved modeling of pebble beds region: thermal conductivity temperature and strain (for Be) dependent thermal contact resistance temperature dependent. Thermal contact resistance between pebble beds and structural material: correlations from Yagi & Kuni used to define the HTC between pebble beds and structural material: 9 | Recent developments in the design of the EU HCPB-TBM, Fabio Cismondi Improved modeling of pebble beds region: thermal conductivity temperature and strain (for Be) dependent thermal contact resistance temperature dependent.

Improved modeling of pebble beds region: 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 x z y ∆y ≈ + 2,09mm ∆y ≈ + 1,96mm 10 | Recent developments in the design of the EU HCPB-TBM, Fabio Cismondi Improved modeling of pebble beds region: thermal conductivity temperature and strain (for Be) dependent thermal contact resistance temperature dependent.

Improved modeling of pebble beds region: 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. 11 | Recent developments in the design of the EU HCPB-TBM, Fabio Cismondi Improved modeling of pebble beds region: thermal conductivity temperature and strain (for Be) dependent thermal contact resistance temperature dependent.

Improved modeling of pebble beds region: 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. 12 | Recent developments in the design of the EU HCPB-TBM, Fabio Cismondi Improved modeling of pebble beds region: thermal conductivity temperature and strain (for Be) dependent thermal contact resistance temperature dependent.

Improved modeling of pebble beds region: 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. 13 | Recent developments in the design of the EU HCPB-TBM, Fabio Cismondi Improved modeling of pebble beds region: thermal conductivity temperature and strain (for Be) dependent thermal contact resistance temperature dependent.

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 Vertical SGs Breeder Unit CFD model Horizontal SGs Cooling Plates 14 | Recent developments in the design of the EU HCPB-TBM, Fabio Cismondi

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 15 | Recent developments in the design of the EU HCPB-TBM, Fabio Cismondi

Transient thermo mechanical analyses of the BU Submodel 2: BU manifold center region BU base design Design improvement: 20mm thick BU backplate and stiffeners 16 | Recent developments in the design of the EU HCPB-TBM, Fabio Cismondi

3 4 9 10 Transient thermo mechanical analyses of the BU M-Tpe damages assessment 3 4 9 10 17 | Recent developments in the design of the EU HCPB-TBM, Fabio Cismondi

3 4 10 Transient thermo mechanical analyses of the BU M-Tipe damages assessment C-Tipe damage assessment 3 4 10 18 | Recent developments in the design of the EU HCPB-TBM, Fabio Cismondi

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. 19 | Recent developments in the design of the EU HCPB-TBM, Fabio Cismondi

Progress in fabrication Complete set of Build To Print CAD drawings performed and Design Description Document (DDD) of the BU released : 20 | Recent developments in the design of the EU HCPB-TBM, Fabio Cismondi

Progress in fabrication Manufacturing of CP mock-ups Qualification of TIG orbital welding Slight bump, poor torch orientation 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) 21 | Recent developments in the design of the EU HCPB-TBM, Fabio Cismondi

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 22 | Recent developments in the design of the EU HCPB-TBM, Fabio Cismondi

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). 23 | Recent developments in the design of the EU HCPB-TBM, Fabio Cismondi

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 24 | Recent developments in the design of the EU HCPB-TBM, Fabio Cismondi

25 | Thermo-mechanical performance of the EU TBMs under a typical ITER transient; Fabio Cismondi