Composite Materials for Nuclear Applications II: Tungsten Composites and TRISO Fuel
Sponsored by: TMS Structural Materials Division, TMS: Nuclear Materials Committee, TMS: Composite Materials Committee, TMS: Mechanical Behavior of Materials Committee, TMS: Advanced Characterization, Testing, and Simulation Committee
Program Organizers: Anne Campbell, Oak Ridge National Laboratory; Dong Liu, University of Oxford; Rick Ubic, Boise State University; Lauren Garrison, Commonwealth Fusion Systems; Peng Xu, Idaho National Laboratory; Johann Riesch, Max-Planck-Insitut Fuer Plasmaphysik

Monday 2:00 PM
March 20, 2023
Room: 24B
Location: SDCC

Session Chair: Johann Riesch, Max-Planck-Institut für Plasmaphysik; Dong Liu, University of Bristol


2:00 PM  Invited
Progress in the Development of Tungsten Fibre-reinforced Copper Composites for Heat Sink Applications in Plasma-facing Components: Alexander Von Mueller1; Maximilian Fuhr1; Katja Hunger1; Patrick Junghanns1; Rudolf Neu1; Johann Riesch1; Jeong-Ha You1; Markus Milwich2; Lena Müller2; Michael Decius3; Selanna Roccella4; 1Max-Planck-Institut fuer Plasmaphysik; 2Deutsche Institute für Textil- und Faserforschung Denkendorf (DITF); 3TEC-KNIT CreativCenter für technische Textilien GmbH; 4ENEA Frascati Research Center
    In future D-T magnetic confinement fusion reactors divertor plasma-facing components (PFCs) will have to sustain intense particle, heat and neutron fluxes. In order that such components are capable of exhausting high heat fluxes during fusion operation reliably PFC heat sink materials with adequate properties as well as sufficient neutron irradiation resistance have to be applied. Currently favoured PFC heat sink materials, i.e. copper (Cu) alloys, suffer from a notable deterioration of mechanical and thermophysical properties under fusion neutron irradiation. A potentially advanced material against this background is a composite reinforced with tungsten (W) fibres that are embedded in a Cu (alloy) matrix. In the present contribution, recent progress regarding the fabrication and characterisation of such composites for PFC applications will be summarised. This will especially include results with respect to the textile processing of thin W filaments to fibrous preforms as well as results regarding corresponding composite material property characterisations.

2:30 PM  
Recent Progress in the Development of Tungsten Fibre-reinforced Tungsten Composite: Johann Riesch1; Jan Coenen2; Alexander Feichtmayer1; Maximilian Fuhr1; Lauren Garrison3; Henri Greuner1; Till Höschen1; Alexander Lau2; Robert Lürbke1; Yiran Mao2; Wolfgang Pantleon4; Daniel Schwalenberg2; Thomas Schwarz-Selinger1; Rudolf Neu1; 1Max-Planck-Insitut Fuer Plasmaphysik; 2Forschungszentrum Jülich; 3Oak Ridge National Laboratory; 4 Technical University of Denmark
    Tungsten fibre-reinforced tungsten composites utilize extrinsic mechanisms to improve the fracture toughness and thus mitigate this drawback. In this contribution, we will present the main characteristics and properties of the composite material with a focus on the recent progress. Drawn potassium-doped W wire is used as a ductile, high strength fibrous reinforcement. We will present current work on understanding its deformation behaviour and the change of it by irradiation damage. The matrix of the composite is formed around woven long fibres or randomly orientated short fibres by chemical vapour deposition (CVD) or powder metallurgy (PM), respectively. Recently, the use of W fibre yarns was established in the CVD process and long fibre-reinforcement was achieved in the PM route. The results of high heat flux tests for both production routes will be shown. Based on these tests and due to success in upscaling, the design of new components has been possible.

2:50 PM  
Is there Residual Stress in Tungsten Fiber Reinforced Tungsten Composites: Hanns Gietl1; Johann Riesch2; T. Höschen2; S. Schönen3; Ch. Le Bourlot4; J-Y. Buffière4; Wolfgang Pantleon5; J.W. Coenen6; 1Idaho National Laboratory; 2Max-Planck-Insitut Fuer Plasmaphysik; 3Forschungszentrum Jülich GmbH, Institut für Energie und Klimaforschung, Partner of the Trilateral Euregio Cluster (TEC), ; 4Laboratoire de Mécanique des Contact et des Solides, INSA de Lyon; 5Technical University of Denmark; 6Forschungszentrum Jülich GmbH, Institut für Energie und Klimaforschung, Partner of the Trilateral Euregio Cluster (TEC)
     The development of materials for plasma facing components is a key challenge on the path to a fusion power plant. Tungsten fiber reinforced tungsten (Wf/W) can overcome the inherent brittleness of tungsten and its embrittlement during operation which are limiting factors for its use.Residual stress is known to have a strong impact on the materials properties of composite materials. For Wf/W it was seen that residual stress is present during push-out and pull-out tests in the single-fiber composites consisting of a drawn W-fiber, an interlayer material like Y2O3 and a CVD tungsten matrix. Residual stress caused by thermal mismatch should be minimal, but the fibers are under tension during matrix deposition. Although residual stress was also confirmed by finite element modelling the absolute amount was still unknown. The objective of this study is to determine the residual stress in Wf/W by means of synchrotron X-Ray transmission diffraction measurements.

3:10 PM  
Effect of Hot Rolling and High Temperature Annealing on the Microstructure and Mechanical Properties of Hot-rolled 90W7Ni3Fe WHA: Md Ershadul Alam1; Charles Henager Jr.2; Jing Wang2; Wahyu Setyawan2; G.R. Odette1; 1University of California, Santa Barbara; 2Pacific Northwest National Laboratory, Richland
    The 90W7Ni3Fe is a ductile phase (DP) toughened tungsten (W)-based heavy metal alloy (WHA) composite that shows much improved tensile strength, ductility and fracture toughness over monolithic W. The effect of hot rolling (HR), and HR plus annealing on the room temperature (RT) mechanical properties of a 90W7Ni3Fe (by wt%) WHA, at different thickness reductions (0, 62, 74 and 87%) has been explored to take advantage from its deformed brick-and-mortar microstructure. The strength and fracture toughness of HR 90W WHA shows that the 0/87% HR alloys experience highest toughness (KJm ≈ 100 MPa√m) along with stable crack growth. In contrast, the 62/74% HR WHA experience fracture, at a lower elastic KIm (≈ 36 MPa√m). The opposite trend is observed in the microhardness and tensile strength. The 1300ºC/24h anneal homogenizes microstructure, and the RT mechanical properties are nearly the same for all HR 90W WHA.

3:30 PM Break

3:50 PM  Invited
W2C-reinforced Tungsten: A Promising Candidate for EU DEMO Divertor Material: Petra Jenus1; Aljaž Iveković1; Matej Kocen1; Anže Abram1; Andreja Šestan Zavašnik1; Sabina Markelj1; Andrei Galatanu2; Magdalena Galatanu3; Elena Tejado4; Jose Ygnacio Pastor4; Marius Wirtz5; Saša Novak1; Gerald Pintsuk5; 1Jožef Stefan Institute; 2National Institute of Materials Physics, Magurele, Romania ; 3National Institute of Materials Physics, Magurele, Romania; 4Dpto. de Ciencia de Materiales-CIME. Universidad Politécnica de Madrid, Spain; 5Institute for Energy and Climate Reseach, Forschungszentrum Juelich GmbH
     Tungsten is considered as the material of choice for the divertor application of fusion power plants due to its intrinsic thermo-physical properties. One main drawback is the recrystallization induced reduction of its mechanical properties at elevated temperatures. The aim of this research was to improve the material properties to be able to sustain plasma-facing conditions, especially to be able to resist high thermal loads imposed on the divertor during operation. The reinforcement of tungsten by incorporation of carbide nanoparticles, resulted in a material with a stable microstructure and promising behaviour. WC nanoparticles were used as a source for the in-situ formation of W2C inclusions in the W matrix during the thermal treatment of powder mixtures with a field assisted sintering technique.This work has been carried out within the framework of the EUROfusion Consortium No633053. The projects ARRS: P2-0087-2, P2-0405-5 and J2-8165 and MAT2015-70780-C4-4-P and S2013/MIT-2862-MULTIMATCHALLENGE are acknowledged.

4:20 PM  
Thermal Properties of Dispersoid-strengthened Tungsten Alloys for Fusion Applications: Chase Hargrove1; Trevor Marchhart1; Nathan Reid2; Xing Wang1; Jean Paul Allain1; 1Pennsylvania State University; 2Oak Ridge National Laboratory
     Tungsten (W) is a candidate as a plasma facing component in the divertor region of fusion tokamaks due to its high yield strength and melting point (3422°C), and low coefficient of linear thermal expansion at elevated temperatures relative to other refractory metals. As a PFC, W will be exposed to short (ms) pulsed heat loads on the order of GW/m2. The effects of carbide additions on the thermal properties of W warrant further study as these are essential to the thermal shock and fatigue response. W-TaC samples fabricated via spark-plasma sintering (SPS) have been shown to possess a lower thermal conductivity than pure W; this behavior is intrinsically dependent on the microstructure. In this work, samples of W-TaC, W-TiC, and W-ZrC are fabricated via SPS. Thermal conductivity is calculated from the measured electrical resistivity. Work supported by DOE Contract DE-SC0021119

4:40 PM  
Oxidation Response of Irradiated and Unirradiated TRISO Fuel: Tyler Gerczak1; Darren Skitt1; Rachel Seibert1; John Hunn1; 1Oak Ridge National Laboratory
    Potential high temperature gas-cooled reactor (HTGR) accident scenarios involve air ingress into the core subjecting the fuel to oxidizing conditions. Understanding the response of tristructural isotropic (TRISO) coated particle fuel under these accident conditions is necessary to develop predictive models. The Furnace for Irradiated TRISO testing (FITT) was implemented at Oak Ridge National Laboratory (ORNL) to conduct thermal exposures under controlled atmospheres of irradiated TRISO fuel from the Advanced Gas Reactor Fuel Development and Qualification (AGR) Program. Unirradiated and irradiated TRISO particles from the AGR-2 and AGR-5/6/7 experiments have been simultaneously subjected to oxidizing conditions in FITT. The experimental conditions spanned 1200–1400ºC for 50–400 h at pO2 2–21%. Results indicate minor variation in oxidation kinetics between the unirradiated and irradiated TRISO particles although clear variations in oxide morphology are observed for exposures 50–100 h.

5:00 PM  
Correlating Heterogeneous Pore Distribution with Stochastic Fracture in the Pyrocarbon Buffer Layer in TRISO Fuel Particles: Yongfeng Zhang1; Aashique Rezwan1; Claire Griesbach1; Ramathasan Thevamaran1; Wen Jiang2; Tyler Gerczak3; Karim Ahmed4; 1University of Wisconsin; 2Idaho National Laboratory ; 3Oak Ridge National Laboratory ; 4Texas University A&M
    The tristructural isotropic (TRISO) fuel particle contains a U-bearing fuel kernel, enclosed by a pyrocarbon buffer, an inner pyrocarbon (IPyC), a SiC, and an outer pyrocarbon (OPyC) shells, respectively. The buffer is made of porous pyrocarbon and experiences fearing, i.e., formation of circumferential or radial cracks, during fuel operation. Both the crack location and orientation are stochastic, influencing the probability of eventual TRISO particle failure. Here, via three-dimensional characterization of porous microstructure using FIB-SEM tomography and finite-element-method (FEM) modeling using the BISON code, a correlation is established between heterogeneous pore distribution with stochastic fracture. Both the average porosity and its fluctuation are found to increase radially experimentally, with elongated pores orientated along the circumferential direction preferentially. Informed by the experiments on porosity distribution, FEM modeling show that the heterogeneous pore distribution dictates the stochastic nature of buffer fracture, which initiates preferentially along the circumferential direction near the buffer-IPyC interface.