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L. Eric Smith, Alain Lebrun IAEA January 2012

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1 L. Eric Smith, Alain Lebrun IAEA January 2012
Implementation Concepts for Unattended Measurement Systems at Enrichment Plants L. Eric Smith, Alain Lebrun IAEA January 2012 Goals: Describe unattended measurement systems being considered by the IAEA Describe thoughts for how such systems might be used to help achieve high-level safeguards objectives Perform preliminary quantitative analysis of concepts: Metric = ability to detect protracted diversion between inspections Not a comprehensive analysis: to aid discussion and to help inform continuing studies and instrument development Many similarities to Boyer et al. (2010 IAEA Symposium), but contrast: Boyer: Inspector perspective and the impact of individual UMS on DA, NDA sampling requirements Smith: --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 output Undeclared (excess) production of normal enrichment levels Higher-than-declared enrichment (e.g. HEU) Implementation objectives Reduce need for routine measurements, sampling during inspections* Ease and expedite cylinder release process for facility operators 2006 IAEA Report: Diversion pathways analysis led to 3 objectives Diversion 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 measurements Undeclared excess production (completeness): Undeclared feed is used to produce undeclared product. Detection requires verification that: Only declared cylinders are connected to the cascade Contents of all cylinders are as declared Potential 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 monitoring Operational Objectives Ideally, 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 MBA Storage MBA Load-cell monitoring Online Enrichment Monitor (OLEM) M(t) for each cylinder High-accuracy E(t) for each cylinder Continuous gas monitoring Ecyl = E(t)*M(t) Unattended Cyl. Verification Station (UCVS) High-accuracy net mass “NDA Seal” for CoK on cylinder contents Assay of blended cylinders MU M235 = Ecyl * MU For this discussion assume 2 MBAs. Process and Storage 3 different unattended measurements systems (blue text) Describe data streams from each instrument Process 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 Monitoring tstart tend M(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 Monitor E(t) ∝ Rgas_186keV (t) * rgas (P, T, t) OLEM Cascade 1 CEMO NaI(Tl) Pressure Temperature Cylinder Cascade 2 Cascade 3 P ~ 40 Torr Load Cell Cascade 4 Header Pump Gas Sampling M(t) P ~ 4 Torr OLEM 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 production OLEM: 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 calculations Gas 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 node E(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 pipe UF6 Header Pipe Mass Spec Analysis High-accuracy E(t) for product and tails Continuous monitoring of gas

6 OLEM Viability Studies: Examples
OLEM Viability Studies: Examples Statistical uncertainty only--systematic uncertainties are not addressed.** Low P: 10 Torr High P: 50 Torr Low D: 100 mg/cm2 High D: 1000 mg/cm2 Performance Targets Tails: 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 header March-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 cylinders Recovery of CoK on cylinders Platform for weight, NDA verification during inspections Mass: Shared-use or IAEA scale NDA**: Hybrid (PNNL), PNEM (LANL), other? Cylinder ID: L2IS, Global Bar Code, other? Surveillance: NGSS UCVS 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 Work Smith (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 feed Challenges Largest 235U flow rate Poor assay accuracy (OLEM wall-deposit issues, UCVS > 6%) Advantages (assuming natural feed) Isotopics are precisely known Cylinders should be homogeneous Baseline Concept No quantitative assay of feed  assume Ecyl = 0.711%  sF ~ 0.0%...if UCVS verifies that Ecyl_UCVS is consistent with feed-cylinder profile OLEM only on product and tails header pipes UCVS quantitative NDA on blended product cylinders

10 Implementation Concepts: Viability Analysis
Overview Scenario: Diversion into MUF or D 235U bias defect in product and tail cylinders SQ = 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 + sT2 Threshold = 3*sMUF PD 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 MUF Question: 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-distribution PD **from C. Norman, IAEA

11 Implementation Concepts: Viability Analysis
Reference Facility: 4,000,000 SWU/year, 0.711%, 3.0%, 0.25% Analysis variables: OLEM s , UCVS sP , blend fraction, balance period Balance Period = 1 month = Baseline Concept

12 Implementation Concepts: Viability Analysis
Balance Period = 1 week

13 Conclusions High-capacity plants require new instruments and approaches Integrated UMS: “Independent” 235U and U balances on 100% flow NDA Seal for cylinder CoK Special treatment of feed PD values (scoping) for protracted diversion are encouraging UMS Role: Rule out protracted diversion between inspections Machines do routine measurements Inspectors do what humans do best (investigate) Many questions and issues ahead…for example Relevance for diversion and excess production scenarios Realistic OLEM and UCVS uncertainties Data security for shared-use instruments Operator impacts, acceptability

14 Additional Information
Additional Information

15 Potential Impacts to Operators
Potential Impacts to Operators Potential Impact Eased and expedited cylinder release process Reduced physical presence of inspectors Reduced sampling requirements on cylinders Cylinder tracking infrastructure OLEM for process control and criticality control Load-cell (and accountancy scale?) data sharing OLEM nodes installed on header pipes (2 per unit); additional P gauges UCVS installation(s) UCVS scans on cylinders moving in/out of MBAs

16 Material Flow and Data Streams
Unblended Product and Tails Cylinders Process MBA UCVS Storage MBA Load Cell OLEM Load Cell: M(t) OLEM: E(t) Ecyl_OLEM = E(t)*M(t) Ecyl_OLEM : sP < 1%, sT < 3% NDA Seal Scale: Mempty , Mfull , sM < 0.1% M235_OLEM = Ecyl_OLEM * MU M235_OLEM : sP < 1%, sT < 3% Facility-Level Data: MU , M235_OLEM , NDA Seal

17 Material Flow and Data Streams
Feed Cylinders Process MBA UCVS Storage MBA Load Cell Load Cell: M(t) Ecyl = known = 0.711% Ecyl : sF ~ 0.0% NDA Seal: “nominal” feed? Scale: Mempty , Mfull , sM < 0.1% M235 = Ecyl * MU M235 : sF ~ 0.1% Facility-Level Data: MU , M235 , NDA Seal

18 Material Flow and Data Streams
Blended Product Cylinders Process MBA UCVS Storage MBA Blending Station Quantitative NDA of Ecyl_UCVS : sP ~ 3 - 6% NDA Seal Scale: Mempty , Mfull , sM < 0.1% M235_UCVS = Ecyl_UCVS * MU M235_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 Objectives Quantitative assay of cylinder enrichment  M235 in each cylinder Measurement scenario: Single measurement of many different cylinders Key metric: Absolute accuracy for quantification of M235 Preliminary accuracy targets: sP < 3%, sF < 6%, sT < 9% for M235 Full-volume interrogation (i.e. sensitive partial defect detection) Unattended operation NDA Seal  Continuity of knowledge on cylinder contents Measurement scenario: Repeated measurements on a single cylinder Key metric: Reproducibility of key signatures and attributes Candidate attributes: E, MU, 234/235, 232/235, 235 spatial distribution Preliminary 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 UF6 Direct measure of U-235, but weakly penetrating Array of spectrometers  axial distribution of U-235 Induced-fission neutrons  U-235 Direct measure of U-235 For thermal interrogating neutrons, only outer layer of UF6 Neutrons from F-19 (a, n)  U-234 U-234 is primary a emitter Neutron escape: ~0.80  full-volume Indirect measure of U-235 Indicator of feed type Neutron-induced g  U-234 Iron as n  g converter Fe-56 + n  Fe-57 + g (7.63,7.65 MeV) Indirect neutron detection 2614-keV g  U-232 “flag” Presence of U-232  reactor recycle feed

23 Performance Metrics for Quantitative Assay
~ ssys_cal sstat ~ ssys_ran Assay Enrichment (%) sNDA2 = sstat2 + ssys_cal2 + ssys_ran2 Declared Enrichment (%) Prediction: ssys_cal > sstat and ssys_ran 23

24 Performance Metrics for NDA Seal
~ ssys_ran Attribute sseal2 = sstat2 + ssys_ran2 Number of Measurements on Same Cylinder Prediction: ssys_ran can be small, so must minimize sstat 24

25 OLEM Uncertainty Budget
Product Material OLEM target for sE *From Smith and Lebrun, IEEE Nuclear Science Symposium, 2011

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