IAEAInternational Atomic Energy Agency

Implementation Concepts for Unattended Measurement Systems at

Enrichment Plants

L. Eric Smith, Alain LebrunIAEA

January 2012

IAEA

 

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

IAEA’s “Model Approach for GCEPs”

How might unattended measurement systems contribute?

*Related work by Boyer, et al. (IAEA Symposium 2010)

High-capacity plants pose implementation challenges for current approaches.

IAEA

 Potential Roles: Unattended Measurement Systems

Storage MBA

Load-cell monitoringOnline Enrichment Monitor

(OLEM)M(t) for each cylinderHigh-accuracy E(t) for each

cylinderContinuous gas monitoring

Ecyl = E(t)*M(t)

Process MBA

Unattended Cyl. Verification Station (UCVS)

High-accuracy net mass“NDA Seal” for CoK on cylinder

contentsAssay of blended cylindersMU

M235 = Ecyl * MU

NaI(Tl)

UF6

Collimator

E(t)

Pressure (Temp)

mComputer

Pressure

Load Cell

Cylinder

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 Concept: Load-Cell Monitoring

tstart tendM(t)

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 Concept: On-Line Enrichment Monitor

P ~ 4 Torr

E(t) ∝ Rgas_186keV (t) * rgas (P, T, t)

NaI(Tl)

CEMO

Header Pump

1) High-accuracy E(t) for product and tails

2) Continuous monitoring of gas

Cascade 1

Cascade 2

Cascade 3

Cascade 4

P ~ 40 Torr

Gas Sampling

Load Cell

UF6

Header Pipe

PressureTemperatu

re

Mass Spec Analysis

CylinderOLEM

M(t)

IAEA

 OLEM Viability Studies: Examples

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

Tota

l Unc

erta

inty

(%)

.

Product

Feed

Tails

E = 5.0%Low P High PHigh D Low D

E = 2.0%Low P High PHigh D Low D

E = 0.711%Low P High PHigh D Low D

E = 0.2%Low P High PHigh D Low D

Low P: 10 TorrHigh P: 50 TorrLow D: 100 mg/cm2

High D: 1000 mg/cm2

Statistical uncertainty only--systematic uncertainties are not addressed.**

**Plot from Smith and Lebrun (IEEE Nuclear Science Symposium, 2011)Related work by Ianakiev (ESARDA 2010) and March-Leuba (personal

communication, 2012)

Performance Targets

Tails: sT < 3%

Feed: sF < 2%

Product: sP < 1%

IAEA

 Concept: Unattended Cylinder Verification Station

Mass: Shared-use or IAEA scale

NDA**: Hybrid (PNNL), PNEM (LANL), other?

Cylinder ID: L2IS, Global Bar Code, other?

Surveillance: NGSS

**from Smith (INMM 2010)

1) Apply and verify “NDA Seal” at MBA boundaries (CoK)

2) Unattended NDA of M235 for blended cylinders3) Recovery of CoK on cylinders4) Platform for weight, NDA verification during

inspections

**Related WorkSmith (IEEE TNS 2010, INMM 2010), McDonald (INMM

2011)Miller (ESARDA 2011)

IAEA

UCVS Viability Studies: Example“Hybrid NDA” for 235U Assay (30B cylinders)

8

sP = 2.5%

**Plot from Smith et al. (INMM 2010)

Intl. Target Value: sP ~ 5%

Hybrid NDA (preliminary)sP ~ 2.5%sF ~ ??sT ~ ??

Other NDA methods?

NDA Seal?

IAEA

 

“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

UMS Implementation Concepts

IAEA

 

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) • sMUF

2 = sF2 + sP

2 + sT2

• Threshold = 3*sMUF

• PD for 1SQ diversion?

Implementation Concepts: Viability AnalysisOverview

**from C. Norman, IAEA

PD

IAEA

 Implementation Concepts: Viability Analysis

kg U/year cylinders/yearFeed Product Tails Feed Product Tails

6 000 000 1 000 000 5 000 000 710 667 592

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 ConceptConcept UCVS s Blend s (SQ) PD (%)

ID Fraction F T Total TotalF P T P OLEM UCVS

1 0.0 1.0 3.0 3.0 0.05 0.00 0.32 0.05 0.42 0.53 13.62 0.0 0.5 1.5 3.0 0.05 0.00 0.16 0.05 0.21 0.27 77.43 0.0 1.0 3.0 3.0 0.30 0.00 0.23 0.30 0.42 0.56 11.04 0.0 1.0 3.0 6.0 0.30 0.00 0.23 0.60 0.42 0.77 4.55 2.00 1.0 3.0 0.0 0.00 0.95 0.33 0.00 0.42 1.09 1.9

s (SQ)P

OLEM s

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 Implementation Concepts: Viability Analysis

Balance Period = 1 week

Concept UCVS s Blend s (SQ) PD (%)ID Fraction F T Total Total

F P T P OLEM UCVS1 0.0 1.0 3.0 3.0 0.05 0.00 0.07 0.01 0.10 0.12 100.02 0.0 0.5 1.5 3.0 0.05 0.00 0.04 0.01 0.05 0.06 100.03 0.0 1.0 3.0 3.0 0.30 0.00 0.05 0.07 0.10 0.13 100.04 0.0 1.0 3.0 6.0 0.30 0.00 0.05 0.14 0.10 0.18 99.65 2.00 1.0 3.0 0.0 0.00 0.22 0.08 0.00 0.10 0.25 83.7

s (SQ)P

OLEM s

IAEA

 

• 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

Conclusions

IAEA

 

Additional Information

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 Potential Impacts to Operators

Potential 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

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 Material Flow and Data Streams

Load Cell: M(t)OLEM: E(t) Ecyl_OLEM = E(t)*M(t)Ecyl_OLEM : sP < 1%, sT <

3%

Process MBA

NDA SealScale: Mempty , Mfull , sM <

0.1% M235_OLEM = Ecyl_OLEM * MU

M235_OLEM : sP < 1%, sT < 3%

OLEM

Load Cell

UCVS Storage MBA

Facility-Level Data: MU , M235_OLEM , NDA Seal

Unblended Product and Tails Cylinders

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 Material Flow and Data Streams

Load Cell: M(t)Ecyl = known = 0.711%Ecyl : sF ~ 0.0%

Process MBA

NDA Seal: “nominal” feed?Scale: Mempty , Mfull , sM < 0.1% M235 = Ecyl * MU

M235 : sF ~ 0.1%

Load Cell

UCVS Storage MBA

Facility-Level Data: MU , M235 , NDA Seal

Feed Cylinders

IAEA

 Material Flow and Data Streams

Process MBA

Quantitative NDA of Ecyl_UCVS : sP ~ 3 - 6%NDA SealScale: Mempty , Mfull , sM < 0.1% M235_UCVS = Ecyl_UCVS * MU

M235_UCVS : sP ~ 3 - 6%

Blending Station

UCVS Storage MBA

Facility-Level Data: MU , M235_UCVS , NDA Seal

Blended Product Cylinders

IAEA

 Implementation Concepts: Viability Analysis

Balance Period = 2 weeks

Concept UCVS s Blend s (SQ) PD (%)ID Fraction F T Total Total

F P T P OLEM UCVS1 0.0 1.0 3.0 3.0 0.05 0.00 0.15 0.02 0.19 0.24 86.92 0.0 0.5 1.5 3.0 0.05 0.00 0.07 0.02 0.10 0.12 100.03 0.0 1.0 3.0 3.0 0.30 0.00 0.11 0.14 0.19 0.26 80.04 0.0 1.0 3.0 6.0 0.30 0.00 0.11 0.28 0.19 0.35 43.15 2.00 1.0 3.0 0.0 0.00 0.44 0.15 0.00 0.19 0.50 15.7

s (SQ)P

OLEM s

IAEA

 

• 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%• Full-volume interrogation (i.e. sensitive partial defect detection)• Unattended operation

UCVS Technical Objectives

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.

IAEA

 

“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.

IAEA

UCVS: Signatures and Attributes For 235U NDA and NDA Seal

Neutrons from F-19 (a, n) U-234U-234 is primary a emitterNeutron escape: ~0.80 full-volumeIndirect measure of U-235Indicator of feed type

Traditional 186-keV g U-235 concentration in outer UF6Direct measure of U-235, but weakly penetratingArray of spectrometers axial distribution of U-235

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

Induced-fission neutrons U-235Direct measure of U-235For thermal interrogating neutrons, only outer layer of UF6

IAEA

Performance Metrics for Quantitative Assay

23

sNDA2 = sstat

2 + ssys_cal2 + ssys_ran

2

Declared Enrichment (%)

Ass

ay E

nric

hmen

t (%

)

sstat~ ssys_cal

Prediction: ssys_cal > sstat and ssys_ran

~ ssys_ran

IAEA

Performance Metrics for NDA Seal

24

sseal2 = sstat

2 + ssys_ran2

Number of Measurements on Same Cylinder

Attr

ibut

e

~ ssys_ran

Prediction: ssys_ran can be small, so must minimize sstat

IAEA

 OLEM Uncertainty BudgetProduct Material

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Unc

erta

inty

Con

tribu

tion

(%)

.

PressureTemperature186-keV: Deposit186-keV: GasTotal

E = 5.0%P = 10 TorrD = 1000

E = 5.0%P = 50 TorrD = 1000

E = 2.0%P = 50 TorrD = 1000

E = 2.0%P = 10 TorrD = 1000

E = 2.0%P = 10 TorrD = 100

E = 5.0%P = 50 TorrD = 100

E = 2.0%P = 50 TorrD = 100

E = 5.0%P = 10 TorrD = 100

E = wt% 235U for gas, depositP = gas pressure (Torr)D = deposit thickness (mg/cm2)

OLEM target for sE

*From Smith and Lebrun, IEEE Nuclear Science Symposium, 2011