Understanding the Radionuclide Source Term for Underground Nuclear Explosions A review of recent research

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1 Understanding the Radionuclide Source Term for Underground Nuclear Explosions A review of recent research Harry Miley Pacific Northwest National Laboratory Disclaimer: The views expressed here do not necessarily reflect the opinion of the United States Government, the United States Department of Energy, or Pacific Northwest National Laboratory.

2 The Radionuclide Source Term How much signal is created in an UGT? Fission source term Activation source term What about backgrounds? How much gets into the atmosphere? Review of historic test releases Leakage experiments Recent test Planned experiments 2

3 Highlights of Results in Recent Work in Sub- Surface Source Terms Carrigan et al, LLNL Gas release experiment New gas transport modeling & experiments Purtschert et al, U Bern Ar-37 background models and measurement campaign Dubasov et al, KRI Underground transport, including in salt Ringbom et al, FOI/PNNL/PTS DPRK 2006 analysis Popov et al, KRI Analysis of historic Semipalatinsk release data Ely et al, PNNL Analysis of US NNSS releases (Nevada Test Site) Biegalski et al, UT Austin Gas transport modeling Hayes et al, PNNL / LLNL New NG release experiments in design 3

4 Introduction to the Nuclear Fission The Chart of the Isotopes contains much of mankind s knowledge about nuclear physics. 4

5 The Nuclear Fission Yield Curve Fission of uranium produces two new atoms About one out of five winds up as xenon 5

6 Production and Decay of Fission Products One kt produces about 3x10 23 radioactive atoms. Most important for monitoring are things like 99 Mo, 131 I, 133 Xe, 135 Xe, 140 La and others. 6

7 How much activation signal is created in an UGT? For fission, the source term is relatively easy 1.45 x times the fission yield For example, for a 1 kt explosion, ~ atoms of 133 Xe (6%) For activation, we have to worry about how many useful target atoms are nearby Key example: neutrons strike calcium to produce Ar-37 α N 40 Ca 37 Ar What about natural backgrounds? 7

8 Effect of Calcium Target Concentration

9 Background Studies 37 Ar Purtschert et al studying 37 Ar soil background Cosmic ray neutrons react with calcium in surface soil Results to date: mbq/m 3 over most of the Earth s surface Activity decreases rapidly with depth Homogenous soil example: Baltenswil site

10 Purtschert: Estimated Ar background Effects of latitude, altitude ASL, Ca concentration

11 Background Studies Xe Key xenon isotopes 133 Xe and 131m Xe 5 days and 12 days Caused by spont. fission of 238 U in soil Calculated with (Haas) and without (Hebel) basis in 222 Rn Similar results PRELIMINARY estimates For kbq/m Xe: ~2 mbq/m 3 131m Xe: ~0.002 mbq/m 3 BUT, physics and chemistry today limit OSI sensitivity to a few mbq/m 3 for ganged samples

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15 The Transport Challenge for Underground Nuclear Tests Containment: Debris may escape engineered or geologic containment to some degree Dilution and decay: limits of IMS detection 15

16 Review: Historical Probability of a Leak KRI analysis of Semipalatinsk results indicates ~50% of tests leaked xenon Small to large quantities Isotope Frequency T 1/2 Fukushima 1 I h 2 I d I h 4 Cs m 5 Ba d 18 6 Rb m 7 Ru d 8 Te h I m Sr h 11 I m 12 Zr d 13 Ru d 14 Ba m 15 Ce d 16 Cs y 410 PNNL analysis of Nevada leaks in DOE/NV-317 Fractional aerosol leakage vs maturity decreases quickly Volatile species favored Average aerosol leak 1 part in 1E7 Little useful Xe data recorded Miley et al J Radioanal Nucl Chem, 248, No. 3 (2001) 16

17 DPRK 2006 analysis Ringbom et al conclude the DPRK 2006 test leaked perhaps 0.7% of Xe-133 Calculations suggest that a leak 100 times SMALLER could have been easily seen by full IMS. The ratio of 133m/133 xenon suggests leakage that occurred one or more hours after the explosion Conclusions No guarantee of leak detectable by IMS An event undetectable by the IMS might be 1,000,000,000,000,000 time more detectable in an OSI scenario. (The typical dilution from a random location to an IMS station is 1E15.) Ringbom et al J Radioanal Nucl Chem (2009) 282:

18 Review: Non-Proliferation Experiment (NPE) A 1kt underground chemical explosion Carrigan et al released SF 6 and 3 He inside explosion Surface observations Spread around suspected epicenter Conclusions Barometric pumping can take significant time Gas seepage pathways (i.e. fractures), not distance, most important Carrigan et al Nature 382, (08 August 1996) and UCRL-ID

19 Zero-Yield Gas Experiment Legacy test location Drill rig or pre-existing access port Inject radioactive noble gas With overpressure Without overpressure Detect leakage in OSI mode Repeat in different locations and weather Xe Existing nuclear test cavity Realistic fracturing Realistic geometry 19

20 Preliminary work by Justin Lowrey of UT Austin shows that Xe subsurface ratios can depend on geological values like fracture size and fracture separation.

21 Summary / Conclusions Today there are still interesting scientific questions about activation source terms and fission + activation backgrounds in the subsurface. Despite past results and future plans discussed here, the transport of signal from the test to the surface is comparatively under studied compared to waveform Key conclusion of ISS09: more RN transport study

22 Questions?