Broadway, Jeramie W.

Hickman, Robert R.

Mireles, Omar R.

NASA Technical Reports Server

www.nasa.gov Predecisional: For Planning Purposes Only 
Affordable Development and Optimization 
of CERMET Fuels for NTP Ground Testing 
 
Nuclear Cryogenic Propulsion Stage (NCPS) 
Advanced Exploration System (AES) Project 
Robert Hickman 
Jeramie Broadway, Omar Mireles 
NASA  Marshall Space Flight Center 
 
 
Nuclear and Emerging 
Technologies for Space (NETS) 
February 24-26, 2014 
https://ntrs.nasa.gov/search.jsp?R=20140010103 2019-08-31T20:29:59+00:00Z
Outline 
• Historical CERMET Fuel Fabrication and Test Data 
• AES FY12-14 Fuel Materials Development 
• Development and Qualification Approach 
• AES FY15-17 Plan 
– Materials and Process Optimization 
– Hot Hydrogen Screening 
– Material Property and Irradiation Testing 
– Cost/Schedule 
• Summary  
 
 
 
 
 
 
 
 
2 
CERMET Fuel Materials 
• CERMET fuels consist of a metal matrix with 
embedded ceramic fuel particles 
– W  matrix (high melting point, H2 compatibility) 
– UO2, UN, (U,Zr)CN  fuel particles 
• Developed in 1960’s as an alternate to 
graphite based fuels 
– Long operating life (>10 hrs, 2500 C) 
– Multiple restart capability at high specific 
impulse (800-900 sec) 
• Improved fission product retention 
• Metal phase improves toughness 
3 
ANL 2000MW CERMET Engine W - light phase, UO2 - dark phase 
W-UO2 Materials and Process 
• Current work is based on ANL and GE710 Programs 
– Detailed specifications developed for GE710 
– Extensive capabilities that do not currently exist 
• No qualified fuel fabrication processes 
• Key risk for NTP 
• Must recapture and certify process 
• CERMET fuel loss mechanisms are known 
– Vaporization of UO2 
– Diffusion through pores and cracks 
– Differences in CTE of W matrix and UO2 
– Thermal decomposition of fuel/matrix 
• Proven M&P approaches to inhibit fuel loss 
– Complete surface cladding with tungsten 
– W coated spherical UO2 
– Addition of oxide stabilizers to UO2 
4 
W-UO2 CERMET Samples 
fabricated during ANL Program 
GE710 W-UO2 Fuel Fabrication 
• Powder processing 
– Sieving, weighing, and blending 
– Isostatic pressing of fuel segments (wafers) 
– Hydrogen sintering (consolidation of segments) 
• Fuel segment machining 
– Face grinding of fuel segments 
– Channel hole drilling 
• Cladding/component fabrication 
– EDM for cladding and HIP can components 
– End plates, inner/outer cladding tubes 
• Assembly and bonding process 
– Stacking of fuel segments 
– Insertion of cladding tubes 
– E-beam welding of HIP cans 
– HIP bonding of integrated assembly 
• Successfully fabricated and tested numerous elements 
5 
OD Cladding 
Tubes 
Fuel Segment 
ID Cladding 
Tubes 
W-UO2 CERMET Test Data 
• Limited data available with a large variation in 
starting materials, processing, and testing 
• Surface claddings enhance fuel retention and 
thermal cyclic life 
– 27 wt% loss in unclad vs. 3 wt% for clad samples 
• Particle coatings shown to improve UO2 
distribution and provide continuous W matrix 
• 23 wt% loss at 2500 C for 2 hours vs. 0.8 wt% 
loss of samples with W coated UO2 
• Addition of oxide stabilizers decrease fuel loss 
by preventing the reduction of UO2 
 
6 
Powder Coated 
Particles 
Vapor Coated 
Particles 
Uncoated 
Particles 
Charts courtesy of Jon Webb, 
“Literature Review of Historical W-
UO2 Fabrication and Testing 
Efforts”, Idaho National 
Laboratories, Internal Document. 
GE710 Irradiation Testing 
• No in-pile testing at current prototypic NTR conditions 
• Majority of samples tested at low temps and longer durations 
– 1500C, 1000’s of hours 
• Fission gas containment to burn up levels exceeding 9x1019 fissions/cm3 
– Equivalent to dozens of Mars missions 
7 
FY12-14 NCPS CERMET Development 
• UO2 feedstocks (ORNL sol gel, CSNR alginate) 
• Powder handling (glove box sieving, blending, filling) 
• CVD W coated UO2 spheres, W claddings 
• Hot Isostatic Pressing (HIP) 
• Post Machining (sectioning, grinding) 
• Compact Fuel Element Testing (CFEET) 
• Successful fab/test of W-UO2 sample 
8 
W/ZrO2 
W Clad 
Dedicated Depleted Uranium Labs 
W-UO2 Samples 
CERMET Fuel Development Path 
9 
Fuel Materials
& Process
Optimization Hot Hydrogen 
Screening
(CFEET)Hot Hydrogen 
Screening
(NTREES)
Material Property & 
Irradiation Testing
CoDR
PDR
CDR
Flight Technology 
Demo Mission
Sub-Element
Testing
Fuel Element
Qualification
Reactor/Engine 
System Test
System Milestones
Pre-ATP Activities (FY15-17)
Post-ATP Activities
Ground 
Test ATP
AES FY12-14
Successful Fuel Element Fab/Test
ATP - Authority to Proceed for Major Program
Fuel Development and Qualification 
• “Certify” fuel material and fabrication process 
• Separate effects testing 
– Thermal chemical and cyclic stability in H2 
– Irradiation for fission tolerance and retention 
• Combined effects testing ($$$$) 
– Radiation, temperature, H2, and pressure 
– Subscale HFIR or ATR 
– Single element and/or bundle in ATR 
– Nuclear Furnace? 
• High cost for prototypic testing 
• Affordable option-separate effects and fuel 
modeling to eliminate combined effects? 
– What are the risks for engine ground test? 
 
10 
FY15-17 Development and Optimization 
• Goal is to mature fuel for future ground test program 
– Enable qualification and production in FY17-20?? 
– Develop basis for performance, production cost and schedule 
• Complete M&P development and characterization 
– Understand processing-microstructure-property relationships 
– Extensive subscale screening in H2 
– Baseline materials, properties, and specifications 
– Demonstrate prototypical performance of fuel 
• Most of the capabilities currently exist to meet FY15-17 goals 
– May require upgrades for LEU (HEU facility does not exist for fuel fab) 
• Limited material properties and irradiation screening 
• Testing and modeling to anchor designs & performance 
– Structural, thermal, chemical, and neutronics 
– Separate effects testing to validate 
11 
CERMET Fuel Development Timeline 
12 
• Iterative M&P optimization and subscale H2 screening 
• Continuous improvement and validation of modeling 
• Validation of fuel element design and performance 
 
Hot Hydrogen Testing
CFEET
NTREES
Modeling/Analysis
Irradiation/Properties Assess capability/needs Fab and test
FY15 FY16 FY17
Verify microstructure, phases, chemistry
Develop material specs
Stability vs temp/duration/cycles
Materials and 
Process 
Optimization
Define fab rqmts
Assess structural, thermal, chemical performance
Ground Test 
ATP
Validated Fuel 
M&P Dev
Complete
CERMET Fuel Development Tasks 
• UO2 feedstock (spheres) 
– Sol Gel (ORNL) 
– Ammonium Alginate (CSNR) 
– Develop particle size constraints, yields, etc. 
• W coated UO2 (MSFC) 
– Optimize processing of various size UO2 spheres 
– Develop production approach 
• W-UO2 fuel segment consolidation 
– Hot Isostatic Press (MSFC) 
• Full length net shape consolidation 
• Integral claddings 
– Spark Plasma Sintering (CSNR) 
• Similar to GE710 but improved consolidation 
• Stacked and bonded segments/claddings 
• Net shape fabrication of cooling channels 
13 
UO2 Spheres 
UO2 CERMET (CSNR) 
W/ZrO2 
W Clad 
W Clad CERMET (MSFC) 
(CSNR) (ORNL) 
CERMET Fuel Development Tasks 
• Hot hydrogen testing (MSFC) 
– Subscale screening in CFEET 
– Full length validation in NTREES 
• Material characterization (MSFC, INL) 
– Consolidated microstructure, phases, density 
– Chemistry 
– Fuel loss and migration  
• Material properties (MSFC, INL, Industry) 
– Thermal expansion, conductivity (diffusivity, specific heat) 
– Tensile, modulus, bend ductility 
• Production facility study (NASA, INL, Industry) 
– Process needs, location, facility requirements, etc. 
14 
H2 Testing of W-UO2 
sample at MSFC 
FY15-17 Irradiation Testing 
• Irradiation may not be a key driver in fuel failure/design 
– GE710 fuel “qualified” for 100 hours at 2148 C with minimal testing 
– Must be verified to understand risk 
– Combined effects testing required at some point for qualification 
• Irradiation testing (ORNL, INL, or University) 
– LEU or HEU? (need fission heating) 
– Subject samples to nuclear environment 
– Evaluate fission product tolerance and containment 
– Dimensional stability and swelling 
– Perform post test metallographic evaluation 
• Limitations 
– Temperature, pressure, and H2 environment 
– How much can we really learn? 
• Goal is to develop basis for future qualification 
 15 
Cost/Risks 
• Costs 
– Costs comparable to current AES effort 
– More funding for DOE and Industry participation 
– Characterization capability does not exist at NASA 
• Risks 
– RF heating/NTREES may not work for validating fuel element 
– Monolithic designs not feasible (may require segmented design) 
– LEU/HEU required for irradiation testing (no fabrication facility) 
16 
FY15 FY16 FY17
UO2 feedstocks 850 850 850
Fuel Segment Consolidation 750 750 750 $M
Characterization 650 650 650 Total FY15-17 CERMET 15.9
Material Properties 450 600 600 Total FY12-14 CERMET 12.3
Irradiation Testing 150 1150 1150
Modeling/Analysis 600 600 600 $M
Hot Hydrogen Testing 475 625 625 NASA 8.2
Industry 500 500 500 DOE/Industry 7.7
4425 5725 5725
Summary 
• Materials, processing, and fuel failure mechanisms are defined 
from previous ANL and GE710 programs 
• Demonstrated fabrication and testing of W-UO2 samples during 
current AES FY12-14 effort 
– Developed critical capabilities and technologies 
• AES FY15-17 CERMET development and optimization 
– Optimize materials and processes, hot hydrogen screening, irradiation and 
material properties testing to form basis of ground test program 
• What makes this affordable? 
– Existing facilities/capabilities to complete optimization 
– Limited testing to validate fuel and obtain critical irradiation/property data 
– Exploratory irradiation testing 
• Defer expensive in-pile testing until qualification approach is clear 
– Separate effects testing and modeling to evaluate the need for combined 
effects testing in prototypic reactor conditions 
 
17 
Acknowledgements 
• Jim Werner – Idaho National Laboratory (INL) 
 
 
 
Questions? 
18 


Affordable Development and Optimization of CERMET Fuels for NTP Ground Testing

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