Aaron Aoyama

Development Status of a SiC-Foam Based Flow Channel Insert for a U.S.-ITER DCLL TBM

Abstract The U.S.-ITER DCLL (Dual Coolant Liquid Lead) TBM (Test Blanket Module) uses a Flow Channel Insert (FCI), to test the feasibility of high temperature DCLL concepts for future power reactors. The FCI serves a dual function of electrical insulation, to mitigate MHD effects, and thermal insulation to keep steel-PbLi interface temperatures below allowable limits. As a non-structural component, the key performance requirements of the FCI structure are compatibility with PbLi, long-term radiation damage resistance, maintaining insulating properties over the lifetime, adequate insulation even in case of localized failures, and manufacturability. The main loads on the FCI are thermally induced due to through the thickness temperature gradients and due to non-uniform PbLi temperatures along the flow channel (∼1.6 m). A number of SiC-based materials are being developed for FCI applications, including SiC/SiC composites and porous SiC bonded between CVD SiC face sheets. Here, we report on an FCI design based on open-cell SiC-foam material. Thermo-mechanical analysis of this FCI concept indicate that a SiC-foam FCI structure is capable of withstanding anticipated primary and secondary stresses during operation in an ITER TBM environment. A complete 30 cm long prototypical segment of the FCI structure was designed and is being fabricated, demonstrating the SiC-foam based FCI structure to be very low-cost and viability candidate for an ITER TBM FCI structure.

Neutronics Analysis of the Divertor Interferometer Diagnostics Inside the Lower Port #8 Plug of ITER with ATTILA 3-D CAD-Based FEM Code

Abstract The Divertor Interferometer Diagnostics is located inside the 8th lower port plug of ITER and consists of 16 laser beam channels. The beam channels start from windows at the rear vacuum enclosure door of the port and pass through a shield block mounted on a structural sled. The cassette box of the laser beams is mounted on the central divertor cassette and the branching beams pass through the 20-mm gaps between the divertor cassette. Nuclear heating and damage (DPA and helium production) rats are calculated in structure of the divertor components and at the sensitive mirrors that direct the laser beams. Personnel dose rates are also calculated inside the port and at the inter space behind the port enclosure. The Distributed Memory Parallel (DMP) version of ATTILA code, SEVERIAN, is used in assessing the heating and damage rate while the dose rate analysis is performed using the serial ATTILA. A 40-degrees CAD model was constructed based on ALITE03 and ALITE04 MCNP CATIA model. About 1.88M cells were used with Sn32P3 approximation along with a 46n-21γ cross section library based on FENDL2.1.

ASSESSMENT OF THE DCLL TBM THERMOSTRUCTURAL RESPONSE BASED ON ITER DESIGN CRITERIA

Abstract The U.S. Dual Coolant Lead Lithium (DCLL) ITER Test Blanket Module (TBM) is under development for operation in the ITER reactor. The DCLL TBM must satisfy the Structural Design Criteria for ITER In-vessel Components (SDC-IC), which provides rules for the design evaluation and stress analyses of in-vessel mechanical components of ITER with the purpose of ensuring that required safety margins are maintained relative to the types of mechanical damage which might occur as a result of imposed loadings. Primary stresses on the blanket structure come from the pressurization of coolants, the weight of the blanket element, and any electromagnetic forces due to plasma disruptions events. Secondary stresses in the materials due to thermal stress resulting from temperature gradients also contribute to the stress state of the structure. The response to primary stresses will depend on the distribution of loads, the blanket support, as well as material thermo-physical properties, which depend on operating temperatures, loads, fabrication and heat treatment and changes caused by neutron irradiation effects. A detailed structural and thermal analysis of the DCLL TBM under typical loading conditions was performed. Highly stressed locations in the TBM were identified and the stress was broken down into membrane, bending, secondary, and peak stress for evaluating local stress intensities and equivalent stress in order to apply the SDC-IC design rules. Both low- and high temperature damage rules were evaluated to show lack of excessive deformation and negligible thermal creep.

Heat Testing of a Prototypical SiC-Foam-Based Flow Channel Insert

As part of the U.S. ITER test blanket module development effort, several flow channel insert (FCI) concepts using a variety of porous SiC and SiC/SiC composites are being developed. Using porous SiC, prototypes of FCI segments as large as 0.12 m × 0.75 m × 0.015 m were fabricated and heat tested with a maximum ΔT of ~150°C across the FCI walls. In this paper, we report on two heat tests of the FCI prototypes. The first test used radiative heating of the inside of the FCI along with convective cooling of the outside of the FCI, which resulted in a temperature drop of about ~147°C across the FCI wall. The second test involved partial submersion of the FCI structure in liquid PbLi, resulting in an inner wall surface temperature of about 600°C and an outer wall temperature of about 450°C (ΔT ~ 150°C). Detailed thermomechanical analyses of the tests were conducted, and results of the simulations are discussed in the context of actual FCI operating conditions.

Design and Fabrication of a Rectangular He-Cooled Refractory Foam HX-Channel for Divertor Applications

Abstract A rectangular single channel low pressure drop helium-cooled refractory metal heat exchanger (HX) tube for divertor applications was designed and manufactured for testing in the SNL E-beam facility. A unique fabrication feature of the rectangular HX channel design is that all welds, brazes, and joints are located at or near the bottom of the rectangular channel, i.e., far from any heated surface. The HX tube concept uses a thin (˜2mm) layer of open-cell refractory foam bonded underneath the heated surface to enhance heat transfer to the helium coolant. The helium coolant flows through a 2-mm-wide slot and then through the thin foam layer (˜2 mm × 12 mm × 127 mm; H/W/L) from the inlet to the outlet plenum. This design minimizes the path of helium flow through foam to about 11 mm and thus the pressure drop through the porous media is more or less constant along the length of the channel. The concept is scalable for cooling large flat surfaces, such as a flat-plate divertor, without substantially increasing the coolant pressure losses. We present CFD analyses used to optimize the design for minimum pressure drop through the porous media and for highest uniformity of surface temperatures. A design-for-manufacturing concept for a single HX-channel was developed with the goal to minimize welds or joints near heated surfaces. Based on the advanced HX-channel design a number of HX-channels were manufactured using Mo as a surrogate material instead of tungsten.

Design and Fabrication of a Flat-Plate Multichannel He-Cooled Refractory HX for Divertor Applications

Abstract A flat-plate He-cooled divertor would provide a flat surface facing the plasma, would minimize the number of otherwise complex sub-modules needed to cool large areas, and could greatly reduce the complexity of the coolant manifold systems. We recently designed and manufactured a unique flat-plate multichannel refractory metal heat exchanger (HX) that employs open-cell refractory foam to enhance heat transfer from the heated plate to the helium coolant. The structural material of the flat-plate HX box (102 mm wide and 165 mm long) is powder metallurgy molybdenum. Three flat-plate HX boxes were fabricated, two with a heated surface plate made of 4-mm thick Mo, TZM, and one 3-mm thick W. Four supply- and five return ducts, each 4.8 mm wide by 61 mm long run parallel underneath the heated plate. A thin sheet of Mo-foam (˜2 mm × 70 mm × 80 mm; H/W/L) is sandwiched between the ducts and the heated plate. Advantages of using foam are detailed in a separate paper in these proceedings. The supply ducts push helium up towards the heated plate and then circumferentially through the foam into the neighboring return ducts. Key to optimizing the design was achieving uniform helium flow upwards to the heated plate along the entire length of the supply ducts, while simultaneously minimizing end-effects due to the short active duct length (˜80 mm). A series of geometric features were designed to obtain relatively uniform flow distributions throughout the HX box. Here we report on the final design based on CFD analysis and thermo-structural finite element.

Thermo-mechanical analysis of a prototypical SiC foam-based flow channel insert

As part of the US ITER Test Blanket Module development effort several FCI concepts using a variety of porous SiC and SiC/SiC composites are being developed. In this work we report on the thermo-mechanical analysis of a SiC foam-based FCI. Prototypes of FCI segments as large as 0.12 m × 0.75 m × 0.015 m were recently fabricated and heat tested with a maximum ΔT of ∼150 °C across the FCI walls. No visible damage was observed after testing. A detailed thermo-mechanical analysis of the test was conducted and results of the simulations are discussed in context of actual FCI operating conditions.

THERMO-MECHANICAL ANALYSIS OF THE HIBACHI FOIL FOR THE ELECTRA LASER SYSTEM

In support of the High Average Power Laser (HAPL) project the Electra Laser, a KrF Gas Laser system is being developed at NRL. The laser uses high voltage (500 - 800 keV), high current (100 - 500 kA), short pulse (100 - 600 ns) electron beams to pump the 0.14 MPa (20 psi) pressurized KrF gas cell, which is separated from the vacuum region by a 25 μm-thick stainless steel foil, the Hibachi Foil. The foil is made of SUS304, operates between 180 °C and 450 °C, and has typical dimensions of about 0.3 m × 1.0 m. The laser pulses at up to 5 Hz, and the foil is subjected to repetitive thermal and mechanical stresses. In typical experiments, the foil lasts 1000 - 20,000 shots before suffering a catastrophic failure. In an attempt to improve foil performance a variety of design modifications are being considered along with changes in foil material. Earlier Hibachi foil designs used flat foils resting on 0.3 m long square water-cooled supporting ribs (1 cm wide). There is a 3.4 cm gap between ribs. Advanced Hibachi foil concepts are under development using a scalloped foil design. In this paper we report on the comparative thermo-mechanical analysis between flat and scalloped foil geometries. It is demonstrated that the scalloped design reduces stresses to within yield limits of the stainless steel material.

Development Status of the Helium-Cooled Porous Tungsten Heat Exchanger Concept

The development status of a helium cooled refractory metal heat exchanger (HX) concept using tungsten foam for enhanced heat transfer is presented. The HX design is based on azimuthal flow of helium through the foam sandwiched between two concentric tungsten tubes. This concept holds the promise for an efficient and low pressure-drop HX concept for plasma facing components, such as divertors. A prototypical flat-top HX-tube is being manufactured for testing at the high heat flux testing facility at SNL. Concept design optimization requires knowledge of the enhanced heat transfer coefficients due to the foam structure. Solid models of representative metal foams were developed for use in CFD analysis. Initial CFD results show improved heat transfer between the heated wall to the coolant. For a 1-mm thick foam with a specific density of 12% and a pore density of 65 PPI an average heat transfer coefficients of 40 000 W/m2-K was estimated, along with a pressure drop of ~60 kPa. For a 10 MW/m2 surface heat load and an inlet helium temperature of 600degC at a pressure of 4 MPa, maximum structural temperatures were estimated to be 1060degC. This preliminary design has a maximum combined primary plus secondary von Mises stress of less than 600 MPa.

THERMOMECHANICAL ANALYSIS OF THE REVISED U.S. ITER DCLL TEST BLANKET MODULE

Abstract The US Fusion Nuclear Science and Technology program selected the Dual Coolant Lead Lithium (DCLL) concept as the primary Test Blanket Module (TBM) for testing in ITER. The DCLL blanket concept has the potential to be a high-performance DEMO blanket design with a projected thermal efficiency of >40%. Reduced activation ferritic/martensitic (RAF/M) steel is the structural material, helium is used to cool the first wall and blanket structure, and the self-cooled Pb-17Li breeder is circulated for power conversion and tritium extraction. The DCLL TBM has undergone major design changes since 2005. We present here the most recent thermo-mechanical analysis of the newly revised DCLL TBM. The analysis described here is aiming to verify the thermo-mechanical response of the DCLL TBM under relevant normal operating conditions as well as during a loss of coolant accident (LOCA). A full 3-dimensional solid model of the entire DCLL TBM structure was developed, which included FW, top and bottom lids, internal supporting ribs, manifolds, plena, and flexible frame-attachment supports. A coupled thermo-mechanical analysis was performed for both normal- and off-normal operating conditions. Thermal loads included surface heat load, volumetric heating, as well as detailed position- and location dependent heat transfer along all coolant channels. Structural loads incorporated helium coolant pressure loads, self-weight, as well as the weight of the PbLi. Maximum structure temperatures of nearly 560 °C along with a maximum resultant net displacement of more than 10 mm were mapped for normal operating conditions and a number of stress concentration locations were identified. The ITER SDC-IC-1300 criteria were applied to the LOCA analysis results. It is shown that the DCLL TBM exhibits admissible behavior regarding the ITER Design Criteria and that the most recent design modifications did not compromise the structural integrity.