2014 Safeguards Symposium, Vienna Ar- IN ATMOSPHERIC AND SUB-SOIL GASES Roland Purtschert Robin Riedmann Lauren Raghoo
Ar as a Neutron Flux Monitor Atmosphere 40 Ar + n Ar + 4n Natural or Level? Artificial Background Underground 40 Ca + n Ar + Background Level?
Indicators and Sources Xe-135 Xe-133m Xe-133 Xe-131m Ar- Kr-85 9.14 h 2.19 d 11.93 d 10.8 y 5.24 d Nuclear power plant 35 d? reprocessing facility Isotope production (e.g. for medicine) Nuclear explosions After Schlosser 2005 Release rate high medium low Test explosions Xe Isotopes Ar- Plutonium production Kr-85 (Xe Isotopes)
Ar- yield (NR+UNE) Sedan Plowshare Crater (Wikipedia) P C N ( E ) ( E )de E 1 GWth Bq/year [Ca] 4% Fission Fusion BWR ~ 1011 P Ar- (Bq/kT) ~ 5 1014 ~ 7 1015 PWR ~ 1011 HTGR ~ 1014 Matuszek et al, (1973) Fay & Biegalski (2012 Teller, (1968) Studer, (1973) Takano, (2003)
Atmospheric Background Activity 8 3 Ar mbq/m Air 7 -- 6 Caribic 5 4 3 Mean observed Caribic background 1-2 mbq/m3air 2 1 0 2007 2008 2009 2010 2011 2012 Minimal values and theoretically expected tropospheric background ~0.4 mbq/m3air (Lal and Peters, 1973
Isotopic properties and decay mode of Ar- Ar- (τ1/2=35.04 d) decays by electron capture (EC) with a decay energy of 2.8 kev. Isotope ratio Ar/Ar at natural levels in the atmosphere: 10-20 Detection method: Low level counting LLC
Ar Laboratories University of Bern, Switzerland 70 mwe PNNL, USA (Seifert et al, 2013) 30 mwe Sample volume: 50-200 Lair DL 1 mbq/m3air Lead shield and guard counters 100 cc counter
Atmospheric Measurements around Bern to Bern 10 km 500 m 90% < 3 mbq/m3air 3 Values > 3 mbq/m3air 1 Value > 5 mbq/m3air Wind Mühleberg BWR 8 400 MWel 3 Univ. of Bern Near Reactor Ar mbq/m Air 7 -- 6 5 4 3 2 1 0 2007 2008 2009 2010 2011 2012
Oak Ridge High Flux Isotope Reaktor (85 MW) (Fay & Biegalski, 2012) >0.1 mbq/m3air >0.01 mbq/m3air >0.001 mbq/m3air ((From Fay & Biegalski, 2012) Estimated yearly emissions (2010): 0.5 1010 Bq Releases after 26 days operation cycle Dilution to 0.1 mbq/m3air air after tens of kilometres
Ar activities in tropospheric air (Bern) 0 100 mbq/m3 mbq/m3air 3.7 1 mbq/m3 0. 10 km from Bern Observations after 1970 Expected natural background level (Lal and Peters 1969) 0.004 (Loosli et al. 1986) Start Operation of Swiss Power Plants Possibly slightly elevated Ar background in the vicinity of nuclear power plants (1-3 mbq/m3air)
Atmospheric Background Activity? 8 3 Ar mbq/m Air 7 -- 6 Caribic 5 4 3 Caribic 2 1 0 2007 2008 2009 2010 2011 2012
Comparison with results from high-volume samplers in Geneva, Switzerland 100 8 3 ArmBq/m Luft 4 75 50 3 3 25 2 Cs-1 Cs-134 I-131 /5 1 0 Bq/m air 5 3 6 Bq/m3air Ar mbq/m air 7 8 Cs-1 Cs-134 7 I-131/5 75 6 5 50 4 3 25 2 1 0 0 18.03.2011 25.03.2011 01.04.2011 08.04.2011 15.04.2011 100 Mar Apr May J un J ul Aug 0 2011 The increase of Ar coincidence with the increase of Cs134, Cs-1 and I-131 two weeks after the Fukushima event
Hypotheses Reactor Block 4 "It is no exaggeration to say that the fate of Japan and the whole world depends on No. 4 reactor." -Former Japanese Ambassador to Switzerland Mitsuhei Murata to UN Secretary-General Ban Ki-moon (CTV News, Monday, 21 May 2012)
Ar activities in tropospheric air (Bern) 0 100 mbq/m3 mbq/m3air Maximal values after NTE 3.7 1 mbq/m3 0. Observations after 1970 Expected natural background level (Lal and Peters 1969) 0.004 (Loosli et al. 1986) Elevated Values after Nuclear Test Explosions (NTE)
Measurements in Bern atmospheric air t: 2 weeks 3 Ar (mbq/m ) 1 Assumptions Ar- Production/MT 1018 Bq (Takano, 2003) Total yield: 7 MT (Lawson, 1994) Homogeneous mixing in northern troposphere (10 km -> V= 2 1018 m3) Measured value in Bern: 70 mbq/m3air atmospheric mixing + decay 100 10 [Loosli et al. 1970,1973, 1986, ] decay (t1/2: 35 d) 70 10 3 18 2 10 7 1018 0.1 1970 Jun Sep 1972 1971 Dec Mar Jun Sep Dec Mar Date Novia Semlya, Semipalatinsk (UDSSR), 7 MT, underground 2% Typical release rate after UNE ~1-10 %
DPRK Test: 2006: Ar- results measured in Bern Detection probability Ar- Produktion/kT 1014 Bq (Takano, 2003) Yield 1 kt Decay time 1 month (factor 2) Mixing in northern hemisphere (V=2 1018 m3) Release rate 10% (Saey et al, 2007) Expected signal: 0.003 mbq/m3 No Ar anomalies detectable in Bern because of large distance dilution
Ar sampling in Tokyo after the 2013 DPNK nuclear test SPEEDI simulations (System for Prediction of Environmental Emergency Dose Information) 2/14 9:00(JST) temp:3.2c wind:nnw 1.1m/s Ar- 3±2 mbq/m3air 2/15 9:00(JST) temp:3.6c wind:nnw 1.4m/s Ar- <5 mbq/m3air No Ar anomalies detected in plume over Japan because of missing release vent (Xe-131m and Xe-133 detected 55 days after the event; CTBTO 2013)
From IMS to OSI OSI: On-Site Inspection
OSI: Soil gas sampling Soil gas sampling 2-10 m
Ar in the shallow alluvium From Riedmann & Purtschert 2011 Sun and Carrigan, 2012 Ar concentrations in soils depend on Sampling depth Geology (Ca concentration, soil permeability) Geographical location (altitude and latitude) Ranges 1-100 mbq/m3air over most of the Earths surface
Global scaling of Ar production at 70 cm depth in relation to a reference site (120 mbq/m 3 air) 1000 mbq/m3air 100 mbq/m3air 20 mbq/m3air Ca content from harmonized world soil database Production scaled to latitude and altitude 5' x 5' resolution From Riedmann & Purtschert 2011
OSI Ar detection system Movable Ar Rapid Detection System (MARDS) Institute of Nuclear Physics and Chemistry, Mianyang, China Sample volume: >200 L Preparation and counting time: 3-4 h DL > 20 Bq/m3air,
Mards System Detection Limit H. Miley, PNNL, 2011
Conclusions High precision Ar measurement provide a sensitive tool for the detection of elevated n-fluxes On a regional scale in the atmosphere (IMS) On a local scale In the underground (OSI) Background activities are low and likely < 3 mbq/m3 in the atmosphere air <100 mbq/m3soil-air in the underground Completing Ar samples taken in the frame of XeIMS would be a valuable and non-ambiguous indicator for clandestine high n-flux activities More investigations are needed about activation source terms in the environment (power plants, deep lithosphere, stratosphere)