Bradley, David E.

Hickman, Robert R.

Mireles, Omar R.

NASA Technical Reports Server

2201 
LOW COST NUCLEAR THERMAL 
ROCKET CERMET FUEL ELEMENT 
ENVIRONMENT TESTING (CFEET) 
David E. Bradley 
 
Nuclear Systems, NASA MSFC 
Huntsville, AL 
 
DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. 
https://ntrs.nasa.gov/search.jsp?R=20120002970 2019-08-30T19:26:07+00:00Z
Purpose of Test Hardware 
• Low-Cost, small scale testing of NTR fuel 
element samples to obtain non-fissile 
materials data. 
• Concentrated heating of fuel sample to near-
prototypical temperatures (and expose to 
Hydrogen) to identify material failure modes. 
• Allow for rapid turnaround testing of fuel 
elements manufactured using variety of 
materials and techniques. 
Illustration of Test Setup 
Vacuum Chamber 
Fuel Element 
Pyrometer 
Sight Glass RF Coil 
Fuel Element 
Pedestal 
Pyrometers 
Test Setup Dimensions 
RF Coil, Fuel Element, Pyrometer Detail 
Fuel Sample 
Pedestal 
Details 
Vacuum Chamber Setup – front view 
Analog Vacuum 
Gauge – since replaced 
by digital sender. 
Chamber Relief 
Valve 
Pyrometer Sight 
Glass 
Vacuum Chamber 
RF Coil 
Feedthrough 
Vacuum Chamber Setup – rear view 
Chamber Relief 
Valve 
Turbo Pump 
Vacuum Chamber 
Turbo Pump 
Isolation Valve 
Roughing Pump 
(under table) 
Pyrometer 
Sight Glass 
View Inside Vac Chamber Showing RF Coil 
Non-Contact Pyrometers 
Vacuum Chamber 
Sight Glass 
FAR Pyrometer 
Lens and Optical 
Fiber 
Mikron M770S 
Pyrometer 
View Into Sight Glass During Heating Test 
Temperature Scale Shown for Reference – NOT ACTUAL ELEMENT TEMPERATURE 
* http://www.blksmth.com/heat_colors.htm 
Data Plot from 1.5kW Non-Melt Test of 
308 stainless steel sample 
201106241306 winplot format.csv
M
ik
ro
n 
Py
ro
m
et
er
 8
00
 - 
15
00
°C
,F
AR
 P
yr
om
et
er
 L
ow
 8
00
 - 
25
00
°C
,R
F 
Po
we
r 0
 - 
15
 k
W
Ed
it 
w/
m
en
u 
St
yl
e-
>N
om
en
cl
at
ur
e-
>S
et
 S
ub
-T
itl
e
105 200 295 390 485 580 675 770
1200
1000
800
600
400
200
0
1200
1000
800
600
400
200
0
2.0
1.5
1.0
0.5
0.0
-0.5
-1.0
Time sec        Mikron Pyro    FAR Pyrom     RF Power 0  
WinPlot v4.50
1:43:18PM 06/24/2011
Mikron Pyrometer 800 - 150   FAR Pyrometer Low 800 - 2   RFPower 0 - 15 kW   
RF Power 
Mikron Pyrometer (Orange) 
FAR Pyrometer (Green) 
Pyrometer Viewport During Melt Test 
Melt Test Videos 
• melt test view 1.mp4 
• melt test view 2.mp4 
304 Fuel Element in RF Coil Before and After Melt 
Estimated RF Heating Efficiency during 
Melt Test, no shielding 
Thermodynamic Modeling 
• Using simple equations for conduction and 
thermal radiation heat transfer, heat loss rates 
were predicted. 
• Conduction heat loss is proportional to the 
element temperature. 
• Thermal radiation heat loss is proportional to the 
fourth power of element temperature. 
• At higher operating temperatures, thermal 
radiation dominates. 
Shielding Techniques 
• Reducing thermal radiation heat loss from the 
fuel element to the vacuum chamber requires 
a shield of some kind. 
• An Alumina ceramic insulator was fabricated 
to fit between the fuel element and the RF 
coil. 
Alumina Sleeve Insulator as Installed 
Alumina Sleeve Insulator during Test 
Low Power Heating Tests, 
Element Temp During Heating 
600 
700 
800 
900 
1000 
1100 
1200 
1300 
1400 
0 60 120 180 240 300 360 420 480 
Te
m
pe
ra
tu
re
 (°
C)
 
Time (seconds) 
No insulation, vacuum pumps isolated. 
With insulation, vacuum pumps isolated. 
With insulation, vacuum pumps operating. 
No insulation, vacuum pumps operating. 
Low Power Heating Test, 
 Element Temp During Cool Down 
500 
600 
700 
800 
900 
1000 
1100 
1200 
0 60 120 180 240 300 360 420 480 540 600 
Te
m
pe
ra
tu
re
 (°
C)
 
Time (seconds) 
No insulation, vacuum pumps isolated. 
With insulation, vacuum pumps isolated. 
With insulation, vacuum pumps operating. 
No insulation, vacuum pumps operating. 
High Power Heating Tests 
• Some estimate of maximum system 
performance was desired. 
• An in-coil ceramic insulator provided potential 
gains in heating efficiency. 
• A heavier wall Zirconia ceramic insulator was 
cast and installed around a high-melting point 
cermet surrogate fuel element for this testing. 
Cermet Surrogate Fuel Element 
Specifications 
• W: Tungsten, 63% by weight, Cp=132 J/Kg ∙K, MP=3422 °C 
• Rh: Rhenium, 5% by weight, Cp=136 J/Kg∙K, MP=3186 °C 
• HfN: Hafnium Nitride, 32% by weight, Cp≈249 J/Kg∙K, MP= 
3305 °C 
• Sample Mass: 92.881 g 
• Estimated properties (based on mass percentages): Cp=169.8 
J/Kg∙K, MP=3373 °C 
• Dimensions: ½ in. in diameter x 1.5 in. in length 
• Sample Density: 19.2 g/cm3 
RF Coil, Fuel Element and Insulator 
Setup for High Power Test 
Note hole in ceramic insulator 
for pyrometer temperature measurement. 
Time Lapse Photos of High Power Test 
High Power Test Video 
• high power test with W-Rh-HfN.mp4 
High Power Heating 
Fuel Element Temperature Plot 
500 
1000 
1500 
2000 
2500 
38:58.3 41:58.3 44:58.3 47:58.3 50:58.3 53:58.3 
Te
m
pe
ra
tu
re
 (°
C)
 
Time (mm:ss.s) 
FAR Internal Data 
Mikron Pyrometer Data 
High Power Testing Results and Discussion 
• RF Power supply tripped off on high water 
temperature limit (40°C). 
• Water temperature dropped sufficiently to 
resume heating after about 60 seconds. 
• Maximum fuel element temperature 
achieved: 1931°C 
• Heating was limited by a cooling water limit 
and not insufficient heating power. 
High Power Testing Results and Discussion 
(continued) 
• The hardware was observed post-test and 
physical contact between the in-coil insulator 
and the water-cooled RF coil was detected. 
• Excessive conduction of heat from ceramic 
insulator to cooling water most likely cause of 
high water temperature trip. 
• Eliminating physical contact and increasing 
cooling water flow rate should preclude 
further high temperature water trip. 
System Upgrades – Water Supply 
Custom 6” CONFLAT™ 
RF Power Feed-through 
New RF Coil with 
3/8” diameter Copper 
Tubing 
System Upgrades –  
New Ceramic Insulator with Clearance Fit to Coil 
New RF Coil with 
3/8” diameter Copper 
Tubing 
New Two-Piece 
Ceramic Casting: 
Improves Stress Relief 
Due to Thermal Expansion 
Cermet Sample 
Upcoming Future Work 
• Integrate new and upgraded components into system. 
• Install thermocouples on vacuum chamber outer wall. 
• Run system check-out and ceramic bake-out tests using stainless 
steel sample. 
• Run identical heating power profiles with all available combinations 
of insulation/shielding. 
• Install Tungsten/Rhenium/Hafnium sample in chamber. 
• Bake-out ceramics pulling active vacuum. 
• Hard bolt chamber top flange, pull deepest possible vacuum and 
isolate pumps (observe vacuum decay). 
• Test to highest possible fuel sample temperature or to system 
failure whichever comes first. 
BACKUP CHARTS 
 
RF Power Supply Specs 
• Radyne Flexitune +15 2-255750-001 
• 15kW, 150 VAC, 2400A, 20-60kHz 
FAR Full Spectrum Pyrometer Specs 
• Temperature range 
– FMP2: 800 - 2500°C nominal; lower limit is dependent upon the absorption of 
the optical path and emissivity of the target. 
– FMP2x: 2000 - 4000°C nominal. 
• Resolution: 0.1°C 
• Repeatability: 0.015% 
• Accuracy: 0.15% on gray targets; typically better than 0.75% 
on targets with nongray or changing emissivity or with 
absorbing atmospheres 
• Wavelength range 
– 500 - 1000 nanometers 
Mikron M770S Pyrometer Specs 
• Temperature Range, 600 – 1400°C 
• Accuracy: ±0.5% of full scale span 
• Repeatability: 0.1% of full scale span 
• Temperature Resolution: 1 °C/°F 
• Spectral Response: One or two narrow bands near 
infrared 


Low Cost Nuclear Thermal Rocket Cermet Fuel Element Environment Testing (CFEET)

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