Gerrish, Harold P., Jr.

NASA Technical Reports Server

11
Current Ground Test Options 
for Nuclear Thermal Propulsion
Harold P. Gerrish Jr
Marshall Space Flight Center
February 25, 2014
Agenda
• Past Rover/NERVA Ground Test Options
• Test Cells
• Engine Test Stand
• Current Environmental Regulations
• Scrubber Options
• Nuclear Furnace Demonstration
• ARES Concept
• Borehole Options
• Nevada Test site
• Idaho Engineering Laboratory
• Total Containment Options
• Los Alamos Study
• NASA concept
• Conclusions
https://ntrs.nasa.gov/search.jsp?R=20140008803 2019-08-31T20:21:58+00:00Z
23
Rover/NERVA Test Cells
• Test cells “A” and “C” were used to test all reactor/engines except 
XE’ from 1959-1972 at the Nevada Test Site
• All engines fired upward into open air
• The test cells were re-used after various engine failures
4
Engine Failure at Test Cell C
Video of engine failure After waiting six weeks, the decontamination crew cleaned up the test site 
in two months and prepared for the next test. Average dose .66 rem.[1]
• Phoebus 1A was a 1100 MWt 
engine, which failed from false 
gauge readings and ran out of 
LH2. 
• Emergency shutdown LH2 now 
used.
• 5 other engines followed Phoebus 
1A and were tested at test cell C
Dose rates at test cell C after 
failure. 20% core ejected. [1]
35
Nevada Test Site Operation Safety and 
Health Record 1959-1972
[2]
6
Engine Test Stand-1 (ETS)
• XE’ only engine tested at ETS
• 77,000 gallon LH2 run tank
• Structure made of aluminum
• Engine surrounded by clamshell to provide high altitude simulation and reduce radiation effects on 
facility
• Duct made from 347 SS
• Steam ejectors reduced ambient pressure to 8 psia
• As engine pressure increased to 210 psia, ambient pressure dropped to 1 psia, then rose to 1.6 psia at 
510psia
47
Current Environmental Regulations
Radionuclides released into the air from DOE facilities are regulated by 
the National Emission Standards for Hazardous Air Pollutants (NESHAP 
40 CFR61.90):
Emissions of radionuclides to the ambient air from Department of Energy 
facilities shall not exceed those amounts that would cause any member of 
the public to receive in any year an effective dose equivalent of 10 
mrem/yr.
An effluent treatment system is 
needed for NTP to insure 
emissions remain within regulations 
under all possible operating 
scenarios
8
Effluent Treatment Options
[3]
59
Objectives of Effluent Treatment System (ETS)
1. Ensure that radioactive material entering the ETS remains in the 
subcritical geometry
2. Cool the test article effluent to temperatures acceptable for normal 
engineering materials used
3. Remove particulates and debris from the effluent stream
4. Remove halogens, noble gases, and vapor phase contaminates from 
the effluent stream
5. Flare hydrogen gas to the atmosphere
6. During test operations and accident conditions (including impacts of 
accumulated radiological material in the ETS) the releases are 
reduced to limits derived from the exposure regulation limits for 
workers and the public.
Note: Objectives from the Final EIS of the SNTP program 1993 [4]
10
Effluent Treatment System Concept
1993 SNTP FEIS [4]
611
Nuclear Furnace NF-1
• 44 MW in size and ran on GH2. 4500-5000 MW/m3 power density
• NF-1 test started in Summer 1972 and was last reactor test done before program canceled
• Six runs were made. Final two runs completed without incident
• Exit gas temperature above 4000R for 121 minutes and above 4400R for 109 minutes total
• Composite fuel achieved better corrosion performance, while carbide fuel had cracked 
extensively near center of reactor
• Only Rover/NERVA reactor test with filtered exhaust before burning hydrogen in flare stack and 
operated successfully
[5]
NF-1 Transverse View
12
How did NF-1 Exhaust System Work?
Exhaust System:
• Some water after leaving the reactor is injected into the hydrogen exhaust to reduce temperature to 1100R and help 
capture many fission products released. Most water cooling reactor goes to holdup tank
• Filter is a two stage radial outflow with wire mesh screen
• The water/gas mixture passed through a series of heat exchangers and water separators. Collected water goes to 
waste disposal. Process water cooling the steam jenny and heat exchanger is vented to the atmosphere as steam or 
drained.
• Hydrogen continues through silica gel dryer and heat exchangers
• Dry hydrogen then passes through charcoal trap before the flare stack
• LH2 mixes with the flow to produce temperatures between 250-350R in the charcoal trap 
• Collected water is held for radiation levels to drop with time, filtered, then disposed of in subsurface tile field. 
Contaminated water is filtered before disposal
NF-1 Test Facility
[5]
Reactor:
• Heterogeneous water moderated beryllium 
reflected reactor containing 49 cells (47 
composite and 2 carbide)
• Neutronic control by 6 rotatable drums
• GH2 supplied by tank farm at 3.7 lbs/sec at 
690 psi
• Water flow to assembly is 50 lbs/sec
• Emergency water cooling for 200 seconds 
during shutdown to cool exhaust ducts
713
Radiation Levels in Effluent Exhaust System
• Radiation levels measured at typical 
positions in the exhaust system over 
sufficient length of time
• Measurements taken with gamma ray survey 
meter
• All components measured decay for 8 Ms
with the half life of 140La
• High energy gamma rays in the exhaust 
system was high and slow to decay because 
of 140Xe (13.1 second half life) leading to the 
deposition of 140La on the system surfaces. 
~10 seconds to travel through exhaust 
system
• Radiation level not attenuated greatly by 
steel of exhaust system components
• Decay of 141Ce was also noticed throughout 
the system
Radiation Levels in Effluent Cleanup System after NF-1 Test
Mixture of fission 
products from 235U
140La half life
[5]
14
• Overall, the effluent treatment system was successful
• Pressure drop across filter much larger than expected
• Charcoal trap removed both radiokrypton and radioxenon from gas 
stream
• High energy gamma rays in the exhaust system was high and slow to 
decay because of 140Xe (13.1 second half life) leading to the deposition 
of 140La on the system surfaces.
• Decay of 141Ce was also noticed throughout the system
• The cause for various instrumentation malfunctions was not “fruitful”
NF-1 Exhaust System Lessons Learned
[5]
815
ARES Nuclear Thermal Propulsion Test Facility Concept
Debris Trap
Activated Charcoal 
adsorber Beds
Engine Test Cell
Engine Test Cell with Exhaust Processing Facility
Top View• Thrust=50k lbf• Mass flow=57 lbs/sec
• Isp=875 seconds
• Exit area ratio 15:1
• Thrust Chamber Pressure=450 psia
• Total exhaust temperature= 4860R
• Max single run time 1 hour
[6]
16
Diffuser and LH2 Injection Water Heat Exchanger LN2 Heat Exchanger
Absorber BedsHEPA FilterDebris Trap and Flow Divider
How does the ARES Concept Work?
• Diffuser slows the flow down to subsonic velocity
• LH2 spray injection brings exhaust down to 1800R. 93 lbs/sec
• Debris trap is two stage with large and small debris screens
• Flow divider divides the exhaust stream into as many as four parallel paths
• Water heat exchanger brings gases down to 590R. 3.5 Mgallons
• HEPA filter array to catch fine particulates
• Liquid nitrogen heat exchanger to bring down temperature to 180R. ~.9 Mgallons
• Absorber beds use 8300 lbs of charcoal each
• Flare stack releases hydrogen and burns with the atmosphere
Flare Stack[6]
917
Borehole Option at Nevada Test Site (NTS)
• SAFE-Subsurface Active Filtering of Exhaust. Proposed by Steve Howe in the late 
1990’s.
• Direct NTP into borehole and allow soil to filter exhaust of radioactive particulates 
and noble gases. NTS has unused boreholes ~1200’ deep and ~8’ diameter
• Eliminates many above ground scrubber sections
• Soil permeability is the driving factor for feasibility
• Exhaust entering borehole must be <600 C to avoid damage to borehole casing and 
alluvium soil
Effluent Treatment System
[7]
Engine firing down a borehole
18
How does Borehole Concept Work?
15
20
25
30
35
40
0 20 40 60 80 100 120 140
Bo
re
ho
le
 P
re
ss
ur
e 
(p
si
a)
Time (mins)
100 % thrust
30 % thrust
100% thrust (162 lbs/sec water, 1.41 lbs/sec excess H2) and 
30% thrust (45.2 lbs/sec water and .73 lbs/sec excess H2). [7]
Mass fraction of 85Kr between 1hr and 100 years 
without hydrogen buoyancy. Up to two hours of 
injection. [8]
• Various soil models predict Alluvium 
permeability having potential to keep back 
pressure within 30 psia for long duration 
engine burns
• Exposing the exhaust to the borehole soil at 
deep locations will take the noble fission 
product gases (e.g., 85Kr) a long time to 
reach the surface
10
19
Past Borehole Test Results at NTS
Field Measurements of Alluvium Permeability. Air Injector Setup at 
subscale hole.  [9]
A variety of soil models were used 
to determine borehole 
performance, but each had 
limitations. An investigation of 
other past borehole tests at NTS, 
which could be related to SAFE.
Preliminary Findings:
• The bottom half of the borehole only takes away a few more psi of total pressure with 
permeability. [10]
• Permeability seems best 300-600’ depth [11, 12]
• Permeability drops with source pressure at all depths. [11]
• Flow from laminar to turbulent reduces permeability [11]
• Research tests with alluvium soil represented by graded glass beads shows air 
permeability dropping with increased water content [13]
• Tracer gas (SF6) reached surface within a day about 180’ from bore hole due to possible 
cracks, geology variability, and atmospheric pressure changes [9, 10]
20
Borehole Concept at Idaho National Lab (INL)
• Impermeable interbeds above the water table and below the surface allows the 
exhaust to travel horizontal between the impermeable layers
• Preliminary results indicate better permeability than at NTS
Schematic illustrating 
typical geologic 
stratigraphy
Soil pressure distribution after 2 hours of engine run time
[14]
11
21
Total Containment Concept
• Assume 5000 MW engine 
operating for 33 minutes
• Oxygen is injected in 
hydrogen exhaust to produce 
water vapor and then 
condense to room 
temperatures
• Residual gas can be chilled 
further and stored as a liquid 
for months between tests
• Requires 2 Gg of LOX and 8 
Gg of cooling water
• Burner design a formidable 
problem
• Scheme worthy of closer 
examination
[15]
22
NASA Preliminary Concept for Total Containment
How it works:
• Hot hydrogen exhaust from the NTP is run into a water cooled diffuser. 
• The diffuser transitions the flow from supersonic to subsonic to allow more efficient burning in the afterburner
• O2 rich afterburner-burns all H2; Products include steam, excess O2 and a small fraction of noble gases (e.g., 
xenon and krypton)
• Heat exchanger and water spray pulls heat from steam to lower the temperature and condense to liquid
• Water tank farm collects H20 and radioactive particulates. Drainage is filtered.
• Heat exchanger-cools residual gases to LN2 temperatures (freezes and collects most noble gases). Starts the 
flow of LOX
• LOX dewar stores LO2. Drainage via boil-off
• Meets any standards/regulations for post test release
Strategy:
• Fully contain NTP exhaust during 
burns to achieve as low as 
reasonably achievable (ALARA) for 
the best public and political 
support
• Slowly drain containment vessels 
after radiation levels drop to 
favorable levels. Use licensed 
filters.
H2O
12
23
Conclusions
• Current environmental regulations make ground testing 
more complex than open air tests done for Rover/NERVA
• The current NTP engine design is much lower thrust than 
was used in past ground test studies (50-100 klbf) for the 
various concepts.
• The smaller the engine and shorter the burn time, the 
lower the facility cost
• The selection of the most affordable ground test facility 
needs to also consider the entire ground test facility 
infrastructure required for the various exhaust handling 
concepts
24
References
1. Dewar, J.A., “To the End of the Solar System- The Story of the Nuclear Rocket”, Second Edition, Apogee 
Books 2007, p19, 56, 74, 83, 84,182, 207,
2. Gunn, S. V., “Development of Nuclear Rocket Engine Technology” MSFC NTP short course, 1992, section 
14 page 4, 6, 27
3. Shipers, L.R., and Brockman, J. E., “Effluent Treatment Options for Nuclear thermal Propulsion System 
Ground Tests”, SAND—92-2085C, October 1992.
4. ”Final Environmental Impact statement Space Nuclear thermal Propulsion Program Particle Bed Reactor 
Propulsion Technology Development and Validation,” US Air Force May 1993.
5. Kirk, W. L., “Nuclear Furnace-1 Test Report”, LA-5189-MS, 1973, pp 3, 6, 10, 21-24, 73, 74
6. French, J. V., LaRue, P. F., “Nuclear Thermal Propulsion Ground Test Facility Concept Definition”, ARES 
Report 050250112-004, May 2006. 
7. Howe, S. D., Travis, B., Zerkle, D. K., “SAFE Testing Nuclear Rockets Economically”, STAIF 2003 
paper#242. 
8. Howe, S. D., et al., “Ground Testing a Nuclear Thermal Rocket: Design of a subscale Demonstration 
Experiment”, INL/CON-12-26693 July 2012.
9. Morris, G. A., Snoeberger, D. F., Morris, C. J., Du Val, V. L., “Field Measurements of Permeability of NTS 
Alluvium in Area 10”, Lawrence Radiation Laboratory, UCID-15919, October 1971.
10. Snoeberger, D.F., Morris, C.J., and Morris, G.A.:“Field Measurements of Permeability in NTS Area 9,” 
Lawrence Radiation Laboratory, University of California, August 23, 1971
11. Keller, Carl, Engstrom, Dale, and West, Francis: “In Situ Permeability Measurements for the Event in U1-C,” 
Los Alamos Scientific Laboratory of the University of California, November 1973.
12. Snoeberger, D.F., Morris, C.J., and Morris, G.A.:“Field Measurements of Permeability in NTS Area 9,” 
Lawrence Radiation Laboratory, University of California, August 23, 1971
13. Springer, David, Loaiciga, Hugo, Cullen, Stephen, and Everett, Lorne:“Air Permeability of Porous Materials 
Under Controlled Laboratory Conditions,” Published in Ground Water, Vol. 36, No. 4, July 1998
14. Howe, S.D., McLing, T., McCurry, M., Plummer, M., “Final Report - Assessment of Testing Options for the 
NTR at the INL”, March 2013
15. Bohl, R., Hanson, D., and Edeskuty, F., “Planning for Ground Testing of Nuclear Rockets Engines with 
Today’s Environmental Awareness,” AIAA-1990-2517, pages  8-11.


Current Ground Test Options for Nuclear Thermal Propulsion (NTP)

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