Presentation on theme: "L. Eric Smith, Alain Lebrun IAEA January 2012"— Presentation transcript:
1 L. Eric Smith, Alain Lebrun IAEA January 2012 Implementation Concepts for Unattended Measurement Systems at Enrichment PlantsL. Eric Smith, Alain LebrunIAEAJanuary 2012Goals:Describe unattended measurement systems being considered by the IAEADescribe thoughts for how such systems might be used to help achieve high-level safeguards objectivesPerform preliminary quantitative analysis of concepts: Metric = ability to detect protracted diversion between inspectionsNot a comprehensive analysis: to aid discussion and to help inform continuing studies and instrument developmentMany similarities to Boyer et al. (2010 IAEA Symposium), but contrast:Boyer: Inspector perspective and the impact of individual UMS on DA, NDA sampling requirementsSmith:--Viability of integrating UMS systems to achieve 100% flow verification--Detection of protracted diversion by “diversion into MUF”--More details on unattended instruments, achievable uncertainties, data streams (e.g. feed approach and NDA Seal)
2 IAEA’s “Model Approach for GCEPs” High-capacity plants pose implementation challenges for current approaches.Safeguards objectives: Timely detection of…Diversion from declared input and outputUndeclared (excess) production of normal enrichment levelsHigher-than-declared enrichment (e.g. HEU)Implementation objectivesReduce need for routine measurements, sampling during inspections*Ease and expedite cylinder release process for facility operators2006 IAEA Report: Diversion pathways analysis led to 3 objectivesDiversion of material from declared (correctness): Essentially, “diversion into uncertainties” where small quantities are “skimmed” to avoid detection protracted diversion scenario. Detection requires accurate facility mass balance, especially U-235. Ideally, IAEA would measure 100% of material flow with high-accuracy U-235 assay, but…a) manpower and cost constraints currently require a sampling-based approach heavily dependent on inspections;b) handheld NDA and weight instruments have large uncertainties.Potential safeguards measures: load-cell monitoring + online monitoring + cylinder measurementsUndeclared excess production (completeness): Undeclared feed is used to produce undeclared product. Detection requires verification that:Only declared cylinders are connected to the cascadeContents of all cylinders are as declaredPotential safeguards measures: Measures for material balance calculations can help, but surveillance, random inspections, mailbox are needed to deter and detect undeclared activities.HEU production: ES is highly effective for HEU detection, but is not sufficiently timely for some diversion pathways.Potential safeguards measures: High-accuracy online enrichment monitoringOperational ObjectivesIdeally, new instrumentation approaches should address some of the implementation issues with current approaches, both from IAEA and Operator perspectives. And ideally, there are “win-win” reasons that Safeguards agencies and Operators would consider new instrumentation approaches.How might unattended measurement systems contribute?*Related work by Boyer, et al. (IAEA Symposium 2010)
3 Potential Roles: Unattended Measurement Systems Process MBAStorage MBALoad-cell monitoringOnline Enrichment Monitor (OLEM)M(t) for each cylinderHigh-accuracy E(t) for each cylinderContinuous gas monitoringEcyl = E(t)*M(t)Unattended Cyl. Verification Station (UCVS)High-accuracy net mass“NDA Seal” for CoK on cylinder contentsAssay of blended cylindersMUM235 = Ecyl * MUFor this discussion assume 2 MBAs. Process and Storage3 different unattended measurements systems (blue text)Describe data streams from each instrumentProcess MBA: Bulk MBA where feed cylinders come in and product/tail cylinders come out. All of this material (in cascades and in cylinders) can be considered “in-process in the MBA” until the cylinders exit the process MBA.Outside the process MBA, cylinders are items. Primary objective for UNDA is to ensure that these items remain intact and are not tampered with (i.e. no material is removed or added to any cylinder).
4 Concept: Load-Cell Monitoring Concept: Load-Cell MonitoringtstarttendM(t)Development, testing of load-cell monitoring concepts underway.Concept is simple, but data authentication issues are not. Here, we assume those issues have been solved.Joint-use load cell monitoring provides M(t) for each feed, product and tail cylinder. Start and end weights are authenticated with accountancy scale values from UCVS.M(t) profile is used to weight the E(t) from OLEM in calculation of E_cyl.
5 Concept: On-Line Enrichment Monitor Concept: On-Line Enrichment MonitorE(t) ∝ Rgas_186keV (t) * rgas (P, T, t)OLEMCascade 1CEMONaI(Tl)PressureTemperatureCylinderCascade 2Cascade 3P ~ 40 TorrLoad CellCascade 4Header PumpGas SamplingM(t)P ~ 4 TorrOLEM concept has many similarities to an online instrument that the IAEA already uses: CEMO.CEMO: only on product pipes; low-P side; NaI; no gas density/pressure info; ONLY GOAL: simple Go-No-Go on HEU productionOLEM: on feed, tails, product pipes; high-P side of header; NaI; Gas density calibration from P gauge; GOAL: High-accuracy E(t) to support facility mass balance calculationsGas density: Function of P and T, determined with independent sensors. P sensors should be of same type used by the operator for ease of maintenance.P(t): variations on minutes time-scale, proprietary no xmission from nodeE(t): Net CR in 186 ROI (minus Bkg and wall deposit) is direct measurement of U-235 passing in front of detector. When corrected for gas density, relative enrichment can be calculated.Big Changes from CEMO: High-P side, P(t) data, high-accuracy quantitative, need only 1 per header pipeUF6Header PipeMass Spec AnalysisHigh-accuracy E(t) for product and tailsContinuous monitoring of gas
6 OLEM Viability Studies: Examples OLEM Viability Studies: ExamplesStatistical uncertainty only--systematic uncertainties are not addressed.**Low P: 10 TorrHigh P: 50 TorrLow D: 100 mg/cm2High D: 1000 mg/cm2Performance TargetsTails: sT < 3%Feed: sF < 2%Product: sP < 1%Viability studies, based on simulations and error propagation calculations, have been performed by the IAEA (and recently confirmed by independent calculations by ORNL through SP-1).MCNP modeling of gas and wall-deposit signatures in nominal OLEM design.Analyze bounding scenarios: calculated predicated uncertainties for best-case and worst-case for F, P and T.Compare predicted uncertainties to (somewhat arbitrary) performance targets (dotted lines)Summary: Assuming systematic and calibration uncertainties can be sufficiently minimized, and OLEM instrument may be capable of meeting performance targets, so long as wall deposits are not excessive at the measurement locations.This encouraged development of field prototypes: underway through the USSP at ORNL.Support for instrument uncertainties used in this study:Ianakiev: Field testing of OLEM-like device at Capenhurst on product headerMarch-Leuba: Independent modeling and error propagation (using Monte Carlo method).**Plot from Smith and Lebrun (IEEE Nuclear Science Symposium, 2011)Related work by Ianakiev (ESARDA 2010) and March-Leuba (personal communication, 2012)
7 Concept: Unattended Cylinder Verification Station Apply and verify “NDA Seal” at MBA boundaries (CoK)Unattended NDA of M235 for blended cylindersRecovery of CoK on cylindersPlatform for weight, NDA verification during inspectionsMass: Shared-use or IAEA scaleNDA**: Hybrid (PNNL), PNEM (LANL), other?Cylinder ID: L2IS, Global Bar Code, other?Surveillance: NGSSUCVS Concept has previously focused on only the quantitative NDA role, which under assumptions of a successful OLEM, would be a relatively limited role. Recently, the UCVS role has been expanded to help address the issue of CoK on cylinders, once an initial value for M_235 has been established.“NDA Seal” is this new idea…more on that later. For now, think of the NDA Seal as performing the core function of a traditional seal: insure that the contents of the cylinder are unchanged since the time the seal was applied.In large, modern plants, UCVS could play other important roles:Unattended U-235 assay for blended cylinders, recovery of CoK, platform for more accurate and less manpower-intensive cylinder measurements during inspections.**from Smith (INMM 2010)**Related WorkSmith (IEEE TNS 2010, INMM 2010), McDonald (INMM 2011)Miller (ESARDA 2011)
8 UCVS Viability Studies: Example “Hybrid NDA” for 235U Assay (30B cylinders) Intl. Target Value: sP ~ 5%Hybrid NDA (preliminary)sP ~ 2.5%sF ~ ??sT ~ ??Other NDA methods?NDA Seal?sP = 2.5%Preliminary viability studies for the NDA functions of the UCVS have been performed, through support of US DOE projects at PNNL and LANL. These studies give us initial and encouraging clues about how these instruments might perform.This data is taken from PNNL work on a hybrid NDA method combining gamma-ray spectroscopy with indirect totals neutron detection. Just an example to illustrate the possibilities…Plot: Comparison of assay and declared enrichment values, and calculation of aggregate uncertainty (systematic + statistical) for this small population of 30B product cylinders (ignore natural and depleted…too few for quantitative).Summary result: With instrumentation suitable for unattended cylinder assay, uncertainty on product cylinders 2X lower than ITV values and current handhelds.Yet to be learned through such studies is:--how such methods perform for feed, tail cylinders--how other methods (e.g. PNEM) perform--how candidate methods perform for NDA Seal function. Here, we assume those studies are successful in terms of viability.8**Plot from Smith et al. (INMM 2010)
9 UMS Implementation Concepts “Special” treatment of feedChallengesLargest 235U flow ratePoor assay accuracy (OLEM wall-deposit issues, UCVS > 6%)Advantages (assuming natural feed)Isotopics are precisely knownCylinders should be homogeneousBaseline ConceptNo quantitative assay of feed assume Ecyl = 0.711% sF ~ 0.0%...ifUCVS verifies that Ecyl_UCVS is consistent with feed-cylinder profileOLEM only on product and tails header pipesUCVS quantitative NDA on blended product cylinders
10 Implementation Concepts: Viability Analysis OverviewScenario: Diversion into MUF or D235U bias defect in product and tail cylindersSQ = 75 kg 235U (LEU, NU, DU)Viability Metric: Fidelity of 235U mass balance (“IMUF”)Assume no waste, scrap, etc.IMUF = F – (P + T)sMUF2 = sF2 + sP2 + sT2Threshold = 3*sMUFPD for 1SQ diversion?Diversion Scenario: Operator diverts 1SQ by diverting fraction of cascade flow to undeclared withdrawal stations: F > (P+T)MSA Recommendations: timeliness of 1 month, 25 kg < SQ < 75 kg U-235 (since not specific, we use 75kg as bounding case)Viability analysis uses simplifying assumptions and simplified calculations:--Focus on U-235 balance, as it is ultimate objective--IAEA’s unattended instruments with 100% coverage allow periodic (e.g. monthly or weekly) calculation of U-235 MUFQuestion: What is the probability of detecting protracted diversion of 1SQ?--Calculate sigma_MUF--Assume Threshold (T) = 3*sigma_MUF (IAEA policy <0.1% false positive)--Calculate PD using CDF for 1SQ-distributionPD**from C. Norman, IAEA
12 Implementation Concepts: Viability Analysis Balance Period = 1 week
13 ConclusionsHigh-capacity plants require new instruments and approachesIntegrated UMS: “Independent” 235U and U balances on 100% flowNDA Seal for cylinder CoKSpecial treatment of feedPD values (scoping) for protracted diversion are encouragingUMS Role: Rule out protracted diversion between inspectionsMachines do routine measurementsInspectors do what humans do best (investigate)Many questions and issues ahead…for exampleRelevance for diversion and excess production scenariosRealistic OLEM and UCVS uncertaintiesData security for shared-use instrumentsOperator impacts, acceptability
15 Potential Impacts to Operators Potential Impacts to OperatorsPotential ImpactEased and expedited cylinder release processReduced physical presence of inspectorsReduced sampling requirements on cylindersCylinder tracking infrastructureOLEM for process control and criticality controlLoad-cell (and accountancy scale?) data sharingOLEM nodes installed on header pipes (2 per unit); additional P gaugesUCVS installation(s)UCVS scans on cylinders moving in/out of MBAs
16 Material Flow and Data Streams Unblended Product and Tails CylindersProcess MBAUCVSStorage MBALoad CellOLEMLoad Cell: M(t)OLEM: E(t)Ecyl_OLEM = E(t)*M(t)Ecyl_OLEM : sP < 1%, sT < 3%NDA SealScale: Mempty , Mfull , sM < 0.1%M235_OLEM = Ecyl_OLEM * MUM235_OLEM : sP < 1%, sT < 3%Facility-Level Data: MU , M235_OLEM , NDA Seal
17 Material Flow and Data Streams Feed CylindersProcess MBAUCVSStorage MBALoad CellLoad Cell: M(t)Ecyl = known = 0.711%Ecyl : sF ~ 0.0%NDA Seal: “nominal” feed?Scale: Mempty , Mfull , sM < 0.1%M235 = Ecyl * MUM235 : sF ~ 0.1%Facility-Level Data: MU , M235 , NDA Seal
18 Material Flow and Data Streams Blended Product CylindersProcess MBAUCVSStorage MBABlending StationQuantitative NDA of Ecyl_UCVS : sP ~ 3 - 6%NDA SealScale: Mempty , Mfull , sM < 0.1%M235_UCVS = Ecyl_UCVS * MUM235_UCVS : sP ~ 3 - 6%Facility-Level Data: MU , M235_UCVS , NDA Seal
19 Implementation Concepts: Viability Analysis Balance Period = 2 weeks
20 UCVS Technical Objectives UCVS Technical ObjectivesQuantitative assay of cylinder enrichment M235 in each cylinderMeasurement scenario: Single measurement of many different cylindersKey metric: Absolute accuracy for quantification of M235Preliminary accuracy targets: sP < 3%, sF < 6%, sT < 9% for M235Full-volume interrogation (i.e. sensitive partial defect detection)Unattended operationNDA Seal Continuity of knowledge on cylinder contentsMeasurement scenario: Repeated measurements on a single cylinderKey metric: Reproducibility of key signatures and attributesCandidate attributes: E, MU, 234/235, 232/235, 235 spatial distributionPreliminary uncertainty targets: TBD, but likely < 0.5%The NDA Seal is a recent addition to the potential roles of the UCVS. The concept requires a viability assessment based on measurements and modeling.
21 Reproducibility of these attributes is the key metric. “NDA Seal”Collection of distinguishing signatures and attributes that can be used to provide and recover CoK of the cylinder contents.Reproducibility of these attributes is the key metric.
22 UCVS: Signatures and Attributes For 235U NDA and NDA Seal Traditional 186-keV g U-235 concentration in outer UF6Direct measure of U-235, but weakly penetratingArray of spectrometers axial distribution of U-235Induced-fission neutrons U-235Direct measure of U-235For thermal interrogating neutrons, only outer layer of UF6Neutrons from F-19 (a, n) U-234U-234 is primary a emitterNeutron escape: ~0.80 full-volumeIndirect measure of U-235Indicator of feed typeNeutron-induced g U-234Iron as n g converterFe-56 + n Fe-57 + g (7.63,7.65 MeV)Indirect neutron detection2614-keV g U-232 “flag”Presence of U-232 reactor recycle feed