Measurement of Radioxenon and Argon-37
Released into a Nuclear Explosion Cavity
for Development and Evaluation of
OSI Field Sampling Methods
Khris B. Olsen, Brian D. Milbrath, James C. Hayes, Derek A. Haas,
Paul H. Humble, Randy R. Kirkham, Donny P. Mendoza, Vincent T. Woods,
Pacific Northwest National Laboratory
Richland, WA
Dudley F. Emer
National Security Technologies
Las Vegas, NV
Charles R. Carrigan
Lawrence Livermore National Laboratory
Livermore, CA
June 13, 2013
The views expressed here do not necessarily reflect the opinion of the United States Government,
the United State Department of Energy, or the Pacific Northwest National Laboratory
PNNL-SA-959171
Outline
Why studying noble gas releases is important
Science objectives of our research
Experimental approach and early results
Summary
June 13, 2013
2
Why Studying Noble Gas Releases is
Important
Consider the scenario:
A significant seismic event was detected by the International
Monitoring System (IMS)
The triggering event was possibly a low yield underground test
Yet perhaps no significant radionuclide airborne signature was detected
by remote IMS stations over a few days
Q: How could you clarify the nature of the triggering event?
A: On-Site Inspection (OSI)
Radionuclides may be detectable at ground zero that are far below IMS
detection thresholds
If containment is near complete, the most definitive indication of a nuclear
test, short of drilling, would be the detection of subsurface radioxenon and
37Ar
Subsurface noble gas in excess of background is hard to explain away
June 13, 2013
3
Noble Gas Migration Science Objectives
There have been thousands of studies of the source term of seismic signals
related to earthquakes and mining activity, but only a few nuclear
explosion source term studies
There have been only two previous experimental studies regarding the
detection of noble gas at a test site
Charles Carrigan et al. (1997) *He-3
Yuri Dubasov (2010)
Based on these works, we believe additional experimentation is necessary
to:
Develop an understanding of the gaseous fission product source term for
OSI (and IMS)
Develop a better understanding of subsurface gas migration pathways
Provide empirical data to support subsurface gas migration models
Evaluate sampling methods useful for OSI
Measure subsurface background levels of relevant rare gas isotopes
June 13, 2013
5
Experimental Approach
Produce rare isotopes via reactor
irradiation of targets
36Ar→37Ar
→ 127Xe (longer T1/2 than nuclear
explosion radioxenons)
126Xe
Inject into existing cavity
Use legacy pipe and valve
High concentrations injected to
increase likelihood of detection
Nuclear cavities have an established
fracture network
Sample collection similar to OSI
methods
Measure with best available
technology
Down to background levels
SAUNA for radioxenons
PNNL’s ultra-low background
proportional counters for 37Ar
June 13, 2013
7
7
Aerial View of Experiment Location,
Surface Fissures, and Sampling Locations
8
Sample Analysis:
37Ar
Measurements
Whole air samples are
processed to purify Ar
Measured in a 30 meter
water equivalent
underground cleanroom
Samples are measured
inside a hyper-pure
proportional counter
June 13, 2013
10
Background Radioxenon Analysis Results
Soil gas 133Xe observed
from field site
underground samples
Atmospheric
133Xe observed
at field site
133Xe
observed
from bore hole
(natural)
Atm
Bkg
Richland, WA (atm samples)
June 13, 2013
Base Location (atm samples)
11
Radiotracer Production
127Xe
can be created by irradiating 126Xe with thermal neutrons
{126𝑋𝑒+𝑛→127𝑋𝑒+𝛾}
Half-life is 36 days
Transport: Longer lived surrogate for the radioxenons of interest in OSI
Decays with an electron/photon coincidence signature, so it can be
detected by SAUNA radioxenon systems
37Ar
can be created by irradiating 36Ar with thermal neutrons
{36𝐴𝑟+𝑛→37𝐴𝑟+𝛾}
Half-life is 35 days
Transport: Is one of the isotopes of interest in an OSI
Can be detected with internal gas proportional counters as
demonstrated at PNNL
June 13, 2013
14
Irradiation Details
Stable gases
700 mL enriched 126Xe (>99.9%)
700 mL enriched 36Ar (>99.9%)
Irradiated in the core of the 1.1 megawatt TRIGA reactor at the
University of Texas at Austin
~1013 n cm-2 s-1 thermal neutron flux
June 13, 2013
Model results
15
Injection Scenario for Xe-127 and Ar-37
This test injected 3.7 x 1010 Bq (1 Ci) of 37Ar and 1.1 x 1011 Bq (3 Ci)
127Xe into the cavity
SF6 was co-injected with the radiotracer
Injection occurred at a rate of ~260 scfm for 10 hours
The cavity was not to be over-pressured
During previous chemical tracer injection preparation tests, the cavity
was over-pressured to +30 mbar ambient – 0.03 atmospheres
How do the radiotracer’s quantities compare with a 1 kt nuclear test?
A 1kt fission energy release produces ~1x1016 Bq of 133Xe
Neutrons from a 1 kt test will produce ~1x1013 Bq of 37Ar when conducted
in a location where there is 4% calcium in the surrounding material
June 13, 2013
16
Sampling Approach
Unlike sampling for a chemical
tracer, radioxenon analysis
requires high volume samples
(a few cubic meters)
Each of the sampling sites is
equipped with one or more 2000liter bladder bags
The bladder bag air samples are
compressed into a single SCUBA
tank using a dive air compressor
Eight SCUBA tanks are collected
per sampling event and two
sampling events per week
The 16 SCUBA tank samples are
shipped to PNNL weekly and
analyzed for 127Xe and 37Ar
June 13, 2013
17
Summary
The results of a chemical tracer pre-experiment identified the best
surface and soil gas sampling locations
Background levels of radioxenons have been established in ambient
air at the site and subsurface gas samples from the cavity
This is the first time fission yield radioxenon isotopes have been
measured in background subsurface gas samples!
Those levels are significantly below the levels injected into the cavity
Enriched 126Xe and 36Ar were irradiated to a total activity of 1 Ci of
37Ar and 3 Ci of 127Xe and injected into the cavity without overpressurization and allowed to diffuse to the surface by natural
atmospheric pressure changes
Three sampling events have occurred since injection of the
radiotracers and sample analysis has just begun
June 13, 2013
18
Supporting Information
Related Posters at S&T 2013
T2-P58: Production of High
Activity Radioxenon and
Radioargon Sources for Noble
Gas Migration Tracer Studies,
Derek Haas and Justin McIntyre
T3-P73: Maturing the NG ConOps for RNG – Improved
Sampling Concepts, Jim Hayes
and Ted Bowyer
June 13, 2013
References
Carrigan, C.R., R.A. Heinle, G.B.
Hudson, J.J. Nitao, and J.J
Zucca. 1997. Barometric Gas
Transport Along Faults and Its
Application to Nuclear Test-Ban
Monitoring.UCRL-JC-127585.
Dubasov, Y.V. 2010.
Underground Nuclear
Explosions and Release of
Radioactive Noble Gases.
Pure.Appl. Geophys. 167, 455461. DOI 10.1007/s00024-0090026-z.
19
Acronyms
Acronym
Expanded
CTBTO
Comprehensive Nuclear-Test-Ban Treaty Organization
IMS
International Monitoring System
OSI
On Site Inspection
SAUNA
Swedish Automated Unattended Noble Gas Analyzer
SCUBA
self-contained underwater breathing apparatus
TRIGA
Training, Research, Isotopes, General Atomic
T½
half-life
XIA
X-Ray Instrumentation Associates
June 13, 2013
20
Acknowledgements
The Noble Gas Experiment would not have been possible without the
support of many people from several organizations. The authors wish to
thank the National Nuclear Security Administration, Defense Nuclear
Nonproliferation Research and Development (DNN R&D) for their
sponsorship of the Noble Gas Experiment under contract DE-AC5206NA25946, and the Office of Nuclear Verification for their support of this
presentation.
June 13, 2013
21