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

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 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

June 13, 2013 7

7

Aerial View of Experiment Location,

Surface Fissures, and Sampling Locations

8

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

June 13, 2013 11

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

June 13, 2013 14

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

Irradiation Details

June 13, 2013 15

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

16 June 13, 2013

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

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 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

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 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.

June 13, 2013 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

T ½ 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-AC52-

06NA25946, and the Office of Nuclear Verification for their support of this

presentation.

June 13, 2013 21