Measurement of Radioxenon and Argon-37 Released into a Nuclear Explosion Cavity for Development and Evaluation of OSI Field Sampling Methods

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1 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

2 Outline Why studying noble gas releases is important Science objectives of our research Experimental approach and early results Summary June 13,

3 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 37 Ar Subsurface noble gas in excess of background is hard to explain away June 13,

4 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,

5 Experimental Approach Produce rare isotopes via reactor irradiation of targets 36 Ar 37 Ar 126 Xe 127 Xe (longer T 1/2 than nuclear explosion radioxenons) 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 37 Ar June 13,

6 Aerial View of Experiment Location, Surface Fissures, and Sampling Locations 8

7 Sample Analysis: 37 Ar 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,

8 Background Radioxenon Analysis Results Soil gas 133 Xe observed from field site underground samples Atmospheric 133 Xe observed at field site 133 Xe observed from bore hole (natural) Atm Bkg Richland, WA (atm samples) Base Location (atm samples) June 13,

9 Radiotracer Production 127 Xe can be created by irradiating 126 Xe with thermal neutrons Half-life is 36 days { 126 Xe+n 127 Xe+γ} 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 37 Ar can be created by irradiating 36 Ar with thermal neutrons Half-life is 35 days { 36 Ar+n 37 Ar+γ} 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,

10 Irradiation Details Stable gases 700 ml enriched 126 Xe (>99.9%) 700 ml enriched 36 Ar (>99.9%) Irradiated in the core of the 1.1 megawatt TRIGA reactor at the University of Texas at Austin ~10 13 n cm -2 s -1 thermal neutron flux Model results June 13,

11 Injection Scenario for Xe-127 and Ar-37 This test injected 3.7 x Bq (1 Ci) of 37 Ar and 1.1 x Bq (3 Ci) 127 Xe into the cavity SF 6 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 ~1x10 16 Bq of 133 Xe Neutrons from a 1 kt test will produce ~1x10 13 Bq of 37 Ar when conducted in a location where there is 4% calcium in the surrounding material June 13,

12 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 liter 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 127 Xe and 37 Ar June 13,

13 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 126 Xe and 36 Ar were irradiated to a total activity of 1 Ci of 37 Ar and 3 Ci of 127 Xe 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,

14 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 Con- Ops for RNG Improved Sampling Concepts, Jim Hayes and Ted Bowyer References Carrigan, C.R., R.A. Heinle, G.B. Hudson, J.J. Nitao, and J.J Zucca Barometric Gas Transport Along Faults and Its Application to Nuclear Test-Ban Monitoring.UCRL-JC Dubasov, Y.V Underground Nuclear Explosions and Release of Radioactive Noble Gases. Pure.Appl. Geophys. 167, DOI /s z. June 13,

15 Acronyms Acronym CTBTO IMS OSI SAUNA SCUBA TRIGA T ½ XIA Expanded Comprehensive Nuclear-Test-Ban Treaty Organization International Monitoring System On Site Inspection Swedish Automated Unattended Noble Gas Analyzer self-contained underwater breathing apparatus Training, Research, Isotopes, General Atomic half-life X-Ray Instrumentation Associates June 13,

16 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-AC52-06NA25946, and the Office of Nuclear Verification for their support of this presentation. June 13,