for Development and Evaluation of OSI Field Sampling Methods Khris - - PowerPoint PPT Presentation

June 13, 2013 PNNL-SA-959171

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

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

Outline

Why studying noble gas releases is important Science objectives of our research Experimental approach and early results Summary

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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

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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

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Experimental Approach

Produce rare isotopes via reactor irradiation of targets

36Ar→37Ar 126Xe → 127Xe (longer T1/2 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 37Ar

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

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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

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Background Radioxenon Analysis Results

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Soil gas 133Xe observed from field site underground samples

Atmospheric

133Xe observed

at field site

133Xe observed

from bore hole (natural)

Base Location (atm samples) Richland, WA (atm samples) Atm Bkg

Radiotracer Production

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127Xe can be created by irradiating 126Xe with thermal neutrons

{126𝑌𝑓+𝑜→127𝑌𝑓+𝛿}

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

{36𝐵𝑠+𝑜→37𝐵𝑠+𝛿}

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

Irradiation Details

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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

Model results

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

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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 2000- 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 127Xe and 37Ar

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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 over-

pressurization 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

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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. 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, 455-

• 461. DOI 10.1007/s00024-009-

0026-z.

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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 T ½ half-life XIA X-Ray Instrumentation Associates

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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.

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