The International Monitoring System of CTBTO - Arpa
The International Monitoring System of CTBTO - Arpa
The International Monitoring System of CTBTO - Arpa
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<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> (IMS)<strong>of</strong> the <strong>CTBTO</strong>TWENTY-FIVE YEARSAFTER THE CHERNOBYLACCIDENT: STUDIES,REMARKS AND RECENTFINDINGS21-22-23 June 2011Udine, ItalyBarbara NadalutRadionuclide Engineering OfficerIMS Division/ Engineering and Development SectionRadionuclide <strong>Monitoring</strong> Unitemail: barbara.nadalut@ctbto.orgPreparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty OrganizationProvisional Technical SecretariatVienna <strong>International</strong> CentreP.O. Box 1200, A-1400 ViennaAUSTRIA<strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> Division - Engineering and Development Section Udine - 23-June 2011Page 1
<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong>Overview <strong>of</strong> the presentationPart 1• Introduction <strong>of</strong> the <strong>CTBTO</strong>• Introduction <strong>of</strong> the <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> (IMS)• <strong>The</strong> <strong>CTBTO</strong> Radionuclide <strong>Monitoring</strong> Network• Radionuclide <strong>Monitoring</strong> Stations Overview• Radionuclide Laboratories supporting the IMS NetworkPart 2• Operation <strong>of</strong> Radionuclide <strong>Monitoring</strong> Network, Data Processing andIDC Products• Operational experience <strong>of</strong> <strong>CTBTO</strong> related to the Fukushima nuclearaccident<strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> Division - Engineering and Development Section Udine - 23-June 2011Page 2
<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong>Introduction <strong>of</strong> the <strong>CTBTO</strong><strong>The</strong> primary objective <strong>of</strong> theComprehensive Nuclear Test Ban Treaty (CTBT)is outlawing nuclear test explosions in all environments: in theatmosphere, underground and under water tests,constituting an effective measure <strong>of</strong> nuclear disarmamentand non-proliferation in all its aspects.<strong>The</strong> Treaty was adopted by the United Nations General Assemblyand open for signature in New York on24 September 1996Since then it has been:signed by 182 States and ratified by 154.<strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> Division - Engineering and Development Section Udine - 23-June 2011Page 3
<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong>Introduction <strong>of</strong> the <strong>CTBTO</strong>Status <strong>of</strong> the Treaty in June 2011 (<strong>of</strong>ficial site : www.ctbto.org )
<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong>Introduction <strong>of</strong> the <strong>CTBTO</strong>Comprehensive Nuclear Test Ban Treaty Organization(<strong>CTBTO</strong>)mandates : to achieve the object and purpose <strong>of</strong> the Treaty, to ensure the implementation <strong>of</strong> its provisions, including those forinternational verification <strong>of</strong> compliance with it, to provide a forum for cooperation and consultation among States Parties.A Preparatory Commission for the Organizationwas established by the United Nations on19 November 1996 and located at the Vienna <strong>International</strong> Centre: to establish a global Verification Regime, to monitor compliance with the Treaty to promote the signature and ratification <strong>of</strong> the Treaty, for Entry into Force<strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> Division - Engineering and Development Section Udine - 23-June 2011Page 5
<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong>Introduction <strong>of</strong> the <strong>CTBTO</strong>Comprehensive Nuclear Test Ban Treaty Organization(<strong>CTBTO</strong>)Three main components <strong>of</strong> verification regime: <strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong>: is the global network <strong>of</strong>sensors and devices for detecting and providing evidence <strong>of</strong> possiblenuclear explosions. <strong>The</strong> <strong>International</strong> Data Center: is designed to collect, process,analyse and report on data received from facilities <strong>of</strong> the IMS, includingthe results <strong>of</strong> analyses conducted at certified Radionuclide Laboratories <strong>The</strong> On-Site Inspections: after the entry into force <strong>of</strong> the Treaty,might be requested by States and will have the purpose to clarify whether anuclear explosion has been carried out in violation <strong>of</strong> the Treaty<strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> Division - Engineering and Development Section Udine - 23-June 2011Page 6
<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong>Introduction <strong>of</strong> the IMS<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> (IMS) 321 stations: seismic, hydroacoustic, infrasound and radionuclide 16 radionuclide laboratories to support the IMS network <strong>The</strong> Global Communications Infrastructure to send raw datain near real time to IDC in Vienna for processing and analysis.Requirements?At EIF, data availability is set to 98% for waveformand 95% for RN technologies - which means:Down time per station in one year NO MORE THAN7 DAYS total (waveform)15 DAYS total and 7 DAYS consecutive (RN)!<strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> Division - Engineering and Development Section Udine - 23-June 2011Page 7
<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong>Introduction <strong>of</strong> the IMS<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> (IMS)Layout:AtmosphereTo States PartiesNationalData Centers<strong>International</strong>Data Centerautomated and interactiveknowledge baseddata fusionRadionuclide(Particulateand Noble Gas)(80)HydrosphereHydroacoustic(11)Seismic(50 + 120 )Infrasound(60)Lithosphere
<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong>Introduction <strong>of</strong> the IMS<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> (IMS)PrimarySeismicAuxiliarySeismicRadionuclide Hydroacoustic Infrasound
<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong><strong>The</strong> <strong>CTBTO</strong> Radionuclide <strong>Monitoring</strong> Network<strong>The</strong> Radionuclide <strong>Monitoring</strong> Network80 Radionuclide stations:40 particulate monitoring only and 40 particulate and noble gas monitoring:
<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong>Radionuclide <strong>Monitoring</strong> Stations Overview<strong>The</strong> Radionuclide <strong>Monitoring</strong> NetworkParticulate stations layout:AIR(Compressed) FilterIDCFilter(Compressed) FilterOutletInletAIR SAMPLERDECAYCHAMBERII.GAMMADETECTORCOMPUTER &ELECTRONICSVSATANTENNAIV.I.III.<strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> Division - Engineering and Development Section Udine - 23-June 2011Page 12
<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong>Radionuclide <strong>Monitoring</strong> Stations Overview<strong>The</strong> Radionuclide <strong>Monitoring</strong> NetworkParticulate stations minimum requirements:<strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> Division - Engineering and Development Section Udine - 23-June 2011Page 13
<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong>Radionuclide <strong>Monitoring</strong> Stations Overview<strong>The</strong> Radionuclide <strong>Monitoring</strong> NetworkParticulate manual stations:PGP51 – Papua New GuineaDetection systemCAP14 – CanadaGenerator housingEquipment housingFilter changeSnow White sampler and housing
<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong><strong>The</strong> <strong>CTBTO</strong> Radionuclide <strong>Monitoring</strong> NetworkUFO type air inlet<strong>The</strong> Radionuclide <strong>Monitoring</strong> NetworkParticulate automatic ARAME stations:Robot arm: suctionhead and cutterDetection systemMeasured sampleNew load <strong>of</strong>filter cassettesSampleon filterFilter is cut,piled andmoved tocounting unitUsed filtercassettesSample in decaySample being measuredISP34 - Iceland
<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong>Radionuclide <strong>Monitoring</strong> Stations Overview<strong>The</strong> Radionuclide <strong>Monitoring</strong> NetworkParticulate automatic RASA stations:CLP19 – Easter Islands
<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong>Radionuclide <strong>Monitoring</strong> Stations OverviewAir<strong>The</strong> Radionuclide <strong>Monitoring</strong> NetworkNoble Gas stations sampling process:IIIIIIIVCollection <strong>of</strong> AirGas Processing & Sample Preparation:- Removal <strong>of</strong> water, O 2 , CO 2, Rn (freezetraps, molecular sieves and/or activatedcharcoal)- Producing <strong>of</strong> final concentrated Xe-sampleMeasurement <strong>of</strong>sampled Xenonvolume (GC, TCD)Activity Measurement(HPGe or beta-gammacoincidence)<strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> Division - Engineering and Development Section Udine - 23-June 2011Page 17
<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong>Radionuclide <strong>Monitoring</strong> Stations Overview<strong>The</strong> Radionuclide <strong>Monitoring</strong> NetworkNoble Gas stations minimum requirements:Air flow 0.4 m 3 h -1Total volume <strong>of</strong> sample 10 m 3Collection time 24 hMeasurement time 24 hTime before reporting 48 hReporting frequencyDailyIsotopes measured131mXe, 133 Xe, 133m Xe, 135 XeMeasurement modeBeta-gamma coincidence orHigh resolution gamma spectrometryMinimum Detectable Concentration 1 mBq m -3 for 133 XeState <strong>of</strong> healthStatus data transmitted to IDCCommunicationTwo-wayData availability 95 %Down time 7 consecutive days 15 days annually<strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> Division - Engineering and Development Section Udine - 23-June 2011Page 18
<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong>Radionuclide <strong>Monitoring</strong> Stations Overview<strong>The</strong> Radionuclide <strong>Monitoring</strong> NetworkNoble Gas stations:SAUNA-II, 14 systemsSPALAX, 10 systemsARIX, 3 systems
<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong>Radionuclide Laboratories supporting the Network<strong>The</strong> IMS Radionuclide Laboratories Network16 radionuclide laboratories:10 certified, 6 not certified, 5 with Noble Gas measurements capabilityUSL16CAL05FIL07GBL15RUL13FRL08 ATL03ITL10ILL09CNL06JPL11ARL01BRL04ZAL14AUL02NZL12Buenos Aires (AR), Melbourne (AU), Seibersdorf (AT), Rio de Janeiro (BR), Ottawa (CA), Beijing (CN), Helsinki (FI), Bruyères-le-Châtelle (FR),Yavne (IL), Rome (IT), Tokai (JP), Christchurch (NZ), Moscow (RU), Pelindaba (ZA), Aldermaston (GB), Richland(US)
<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong>Radionuclide Laboratories supporting the Network<strong>The</strong> IMS Radionuclide Laboratories NetworkMinimum requirements for CTBT certified laboratory systems: compliance with these technical specifications (CTBT/PTS/INF.96/Rev.7) is verifiedas part <strong>of</strong> certification process <strong>of</strong> the CTBT detection systems <strong>of</strong> each laboratory.PropertyDetector typeRequirementDetector relative efficiency ≥ 40 %Efficiency calibration measurement rangeEfficiency calibration range (extrapolated)High resolution HPGe46.5–1836 keV30–2700 keVChannels in spectrum ≥ 8192MDA for 140BaWith decay correction to start <strong>of</strong> spectral acquisition, with acquisitiontime no longer than 7 days - For a cylindrical sample geometry with adiameter <strong>of</strong> 70 mm and height <strong>of</strong> up to 6 mmFWHM at 1332.5 keVFWHM at 122.1 keV≤ 24 mBq≤ 2.3 keV≤ 1.3 keVFWTM/FWHM at 1332.5 keV ≤ 2.0<strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> Division - Engineering and Development Section Udine - 23-June 2011Page 21
<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong>Radionuclide Laboratories supporting the Network<strong>The</strong> IMS Radionuclide Laboratories NetworkMinimum requirements for CTBT certified laboratory systems: different techniques are in place or under testing at IMS laboratories inorder to optimise the sensitivity <strong>of</strong> CTBT certified detection systems: ULB gamma detectors in underground laboratories shields and enclosures including clean lead, copper, aluminium radon control methods (LN2 boil-<strong>of</strong>f in measurement chambers) automated recursive energy recalibration techniques detector arrays in coincidence/anticoincidence mode Compton suppression techniques boron absorbers cosmic veto panels<strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> Division - Engineering and Development Section Udine - 23-June 2011Page 22
<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong>Radionuclide Laboratories supporting the Network<strong>The</strong> IMS Radionuclide Laboratories NetworkSupport role <strong>of</strong> radionuclide laboratories:(high -resolution gamma spectrometry only) Station samples for radionuclide network quality assurance (4 per year), station back-up samples when a station is down, samples from station visits, pr<strong>of</strong>iciency test exercise samples, special measurements agreed between the laboratory and the Commission, additional sample analysis <strong>of</strong> a suspect or irregular sample to verify thepresence or absence <strong>of</strong> fission and/or activation productsTrigger: event screening process at the IDC a request <strong>of</strong> a State Party
<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong>Radionuclide Laboratories supporting the Network<strong>The</strong> IMS Radionuclide Laboratories NetworkCategorization <strong>of</strong> CTBT samples: refers to a Standars list <strong>of</strong> 83 CTBT relevant fission/activation products83 CTBT relevant nuclides:RASA split samplesAction: a Level 5 sample is split into 2 partsand sent from the station to 2 differentlaboratories for re-measurementManual split samples
<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong>Operations, Data Processing and IDC Products<strong>The</strong> Radionuclide pipeline
<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong>Operations, Data Processing and IDC Products<strong>The</strong> IDC spectrum analysis s<strong>of</strong>twareSAINT 2(gamma spectrum)ParticulateNORFY(β/γ coincidence spectrum)SPALAXSAUNA / ARIX
<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong>Operations, Data Processing and IDC Products<strong>The</strong> Atmospheric Transport and BacktrackingAtmospheric transport models aredeveloped to determine thedistribution <strong>of</strong> the radioactive cloudin the atmosphere.192 hrs following the release384 hrs following the releaseIn order to locate the event, it isnecessary to have meteorologicaldata for the transport time in orderto backtrack the path <strong>of</strong> the<strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> Division - Engineering and Development Sectionradionuclides to their source point.Udine - 23-June 2011Page 27
<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong>Operations, Data Processing and IDC Products<strong>The</strong> <strong>CTBTO</strong> Secure Website
<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong>Operational experience <strong>of</strong> <strong>CTBTO</strong> (Fukushima)Extract with minor changes from:Operational experience <strong>of</strong> <strong>CTBTO</strong> related tothe Fukushima nuclear accident and long termperspectivesMika Nikkinen, Xuhui Wang, John Coyne, Denys Rousseau, Monika Krysta, Matthias Auer,Robert Werzi, Ulrich Stoehlker, Abdelhakim Gheddou, Dongmei HanPresented by Mika Nikkinenat the S&T Conference in Vienna – 8-10 June 2011Preparatory Commission for theComprehensive Nuclear-Test-Ban Treaty OrganizationProvisional Technical SecretariatVienna <strong>International</strong> CentreP.O. Box 1200, A-1400 Vienna, AUSTRIA<strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> Division - Engineering and Development Section Udine - 23-June 2011Page 29
<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong>Operational experience <strong>of</strong> <strong>CTBTO</strong> (Fukushima)Effects <strong>of</strong> Earthquake, Tsunami and Fukushima NPPaccident on CTBT network Seismic detection <strong>of</strong> Earthquake <strong>of</strong> magnitude nine March 112011 and subsequent several thousand aftershocks Hydroacoustic detection showing the rupture forming under thesea Infrasound detections showing the explosions in the FukushimaNPP Subsequent radioactivity measurements in all the Particulate andNoble gas stations on northern hemisphere and some on SouthernHemisphere.<strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> Division - Engineering and Development Section Udine - 23-June 2011Page 30
Atmospheric transport modeling played important role during thefirst day as there was a need to see which stations are going to be<strong>International</strong>affected<strong>Monitoring</strong> <strong>System</strong>byDivisionthe- Engineeringrelease.and Development Section Udine - 23-June 2011Page 31<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong>Operational experience <strong>of</strong> <strong>CTBTO</strong> (Fukushima)Effects <strong>of</strong> Fukushima NPP accident on CTBT network
Atmospheric transport modeling played important role during thefirst day as there was a need to see which stations are going to be<strong>International</strong>affected<strong>Monitoring</strong> <strong>System</strong>byDivisionthe- Engineeringrelease.and Development Section Udine - 23-June 2011Page 32<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong>Operational experience <strong>of</strong> <strong>CTBTO</strong> (Fukushima)Effects <strong>of</strong> Fukushima NPP accident on CTBT network
cntscnts<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong>Operational experience <strong>of</strong> <strong>CTBTO</strong> (Fukushima)JPP38 (Takasaki, Japan) - Collection 12 – 13 March 2011Spectrum acq. 0-20hSpectrum acq. 20-24hkeVSet <strong>of</strong> gaseous fission products weredetected. Concentrations are notreliable as the sample was on detectorwhen the radioactivity arrived at thestation (visible in spectra collectedlast 4h). Arrival time <strong>of</strong> theseradionuclides is between 2 and 3 am(UTC) on 15/03.Sample is level 5 (multiple fissionproducts detected)<strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> Division - Engineering and Development Section keVUdine - 23-June 2011Page 33
<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong>Operational experience <strong>of</strong> <strong>CTBTO</strong> (Fukushima)Detected isotope concentrations on JPP38, Takasaki, Japan<strong>The</strong> station is 200 km SW from Fukushima. <strong>The</strong> radiation levels detected are low in theglobal scale.<strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> Division - Engineering and Development Section Udine - 23-June 2011Page 34
<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong>Operational experience <strong>of</strong> <strong>CTBTO</strong> (Fukushima)Isotope ratios, JPP38, Takasaki, JapanCs-134 to Cs-137 is behavingsmoothly: predominantlysame type <strong>of</strong> source material.Cs-136 to Cs-137 ratio hassome variation, this mayindicate that source materialhas a mixture <strong>of</strong> differentirradiated batches <strong>of</strong> fuel.Cs-134/Cs-137I-131/Cs-137Cs-136/Cs-137Nb-95/Cs-137La-140/Cs-137Te-132/Cs-137No significant change inmetallic elements vs. Cs-137ratio, gaseous fission productsare dominating.<strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> Division - Engineering and Development Section Udine - 23-June 2011Page 35
<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong>Operational experience <strong>of</strong> <strong>CTBTO</strong> (Fukushima)Detected activity concentrations <strong>of</strong> I-131 (μBq/m3)RN38, Takasaki, Japan RN51 Papua-New Guinea RN70, Sacramento, USARN63, Stockholm, Sweden RN43, Mauritania<strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> Division - Engineering and Development Section Udine - 23-June 2011Page 36
<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong>Operational experience <strong>of</strong> <strong>CTBTO</strong> (Fukushima)Particulate detections at the IMS networkThis picture show time development <strong>of</strong> detections for each day after the accident.Level 5 = multiple fission products detected, Level 4 = one fission products detected, Level 3 = fissionproducts typical for the station detected, Level 1 and 2 = only natural radioactivity detectedSituation end <strong>of</strong> May:more than 40 stations have detected the event and all but closest station (Takasaki, Japan) are back to normalbackground radiation. More than 1600 samples contained radiation originating from Fukushima NPP.
<strong>The</strong> <strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> <strong>of</strong> <strong>CTBTO</strong>Public website: www.ctbto.orgPublic information: info@ctbto.orgDisclaimer: <strong>The</strong> views expressed herein are those <strong>of</strong> the authors and do not necessarily reflect the views <strong>of</strong> theComprehensive Nuclear-Test-Ban Treaty Organization (<strong>CTBTO</strong>) Preparatory Commission. <strong>The</strong> Commission itself takesno responsibility for the content <strong>of</strong> this Technical Presentation.<strong>International</strong> <strong>Monitoring</strong> <strong>System</strong> Division - Engineering and Development Section Udine - 23-June 2011Page 38
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