How To Find the Needle in a Hay Stack: Tracing the History ... · interest. A classic “needle in the haystack” problem performed under strict time pressure. • To make precise

San Diego, 18-22 February 2010 – AAAS Annual Meeting 1

The analysis of particles of nuclear material –finding the proverbial needle in a hay stack

AAAS Annual Meeting – San Diego, February 19, 2010

Klaus LuetzenkirchenInstitute for Transuranium Elements

Joint Research Centre, European Commission Karlsruhe, Germany

http://itu.jrc.ec.europa.eu


The challenge is to measure uranium/plutonium forsafeguards purposes from the

► very large quantities in reprocessing facilities down to

► microparticles as a record of nuclear activities

Nuclear analytical measurements play a key role for• the development of nuclear technology and for • the assurance of its peaceful use

Context of the presentation:


Traditional safeguards- Accountancy of nuclear material in declared facilities (Euratom, IAEA,...)

nuclear reprocessing facilities in Europe and Japan

Strengthened safeguards- Verify absence of undeclared activities (Additional Protocol)

such as enrichment or reprocessinganalysis of particles of nuclear material as an example uranium-235 enrichment measurements

Nuclear forensics- Analysis of seized nuclear material from illicit trafficking


Basics of particle analysis:

• Fine particulate material or aerosols are often released in the handling of nuclear material.

• The particles are representative of the original material and their composition provides specific information about the source.

• The released particles are highly mobile.

• It is difficult to clean up and remove the released particles.

• Samples taken at a facility that has been operated over a long period can provide insight into the entire history of the operation.

picture of a 1-µm uranium particle (D. Simons, NIST) 7 x 10-8 Bq(2.6 x 10-12g)

Sampling of dust at a nuclear facility using a cotton swipe.


The main objectives in particle analysis:

• To search through millions of particles to find the particles of interest. A classic “needle in the haystack” problem performed under strict time pressure.

• To make precise and accurate measurements of the isotopic content of particles, e.g., fissile U-235 versus U-238.

Particle distribution. (Resolution 1050x and 3500x).

Particle Analysis from environmental sampling

235U 238U

U-235 SIMS image U-238 SIMS image


oxygenion beam

particle withnuclear material

uranium ions

Secondary ion mass spectrometer (SIMS)

detector238235

massspectrometer


U235 [mass%]

Num

ber o

f Par

ticle

s

80

70

60

50

40

30

20

10

0

0.5

1.5

Histogram Enrichment Plant A

Reactor Fuel

Feed: U-natural

2.5

3.5

4.5

Normal Production Range

Tails: U-depleted


How to obtain additional information to better characterise the particle history?

Nuclear Forensics of particles

– microstructure / morphology– age – trace elements and impurities from processing– minor isotopes of uranium

U-234: 55 ppm abundance in U-nat, decay product of U-238info on enrichment process

U-236: half life 23.4 million years; abundance in naturepractically zero, produced in nuclear reactors

present in reprocessed feed material









One of three particles found by SIMS (Field 18,21)

How to detect uranium particles in a matrix of “ordinary” material?What is their morphology?

Field 18,21 seen in the SEM

Coupling of SIMS with scanning electron microscopy (SEM)


Transfer between the two instruments SIMS and SEM:Particle search by SIMS (the 300-nm particle was not found by the SEM):

a marker was burnt in the graphite planchet 50 µm to the left of the particle using the SIMS ion beam.

This made it easy to relocate the particle in the SEM for further characterisation.

X-ray spectra emitted from various parts of the particle after excitation by the electron beam

uranium

backscatter mode


Seized MOX powder 1994:

x1000

SEMEDX→ ElementsEl. Diffr. in TEM → Oxides

U3O8hexagons (15%)

PuO2 rods( 5%)

PuO2 platelets (80%)

particle shape →production facility




– microstructure / morphology– age– trace elements and impurities from processing– minor isotopes of uranium





Age = the time elapsed since the last chemical processing (e.g. production, reprocessing, purification)

Rod-shaped

Platelets

240Pu/236UIsotope ratio

Age in 1994 (years):

15.5 ± 0.6

13.9 ± 0.3alpha-decay

MOX powder:









Single particle aerosol mass spectrometry• for each particle analysed, the full mass spectrum is recorded

→ test applicability to single particles from swipe samples

Trace elements:non-nuclear signatures for the characterisation of particles

Experiments performed:• standard uranium particles with different U-235 enrichment• swipe samples from a nuclear facility, previously analysed by SIMS:

→ determine concentration of U containing particles→ identify typical non-nuclear signatures and indicators (particle classes)


200 210 220 230 240 250 260 270 280 2900

50

100

150

2000

50

100

150

200

238

235

UO2+

UO+U+

235U: 10%

inte

nsity

(a.u

.)

mass (m/z)

UO2+UO+U+

235U: 3%

235

238

1 µm uranium oxide particles of different enrichment

Different enrichments can be distinguished (LEU vs. HEU) → potential for detection of (undeclared) uranium enrichment activities

U-235: 3%

U-235: 10%

U+ UO2+UO+238

235

235

238


Classification of particles from swipes:► Ca-oxide + Al, Ba → heavy concrete► uranium appears mainly in this class (3% of total)

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 1500,0

0,2

0,4

0,6

0,8

1,0 23: Na 27: Al 39: K 40: Ca 56: CaO 96: Ca2O

112: Ca2O2

112

96

56

40

39

27

inte

nsity

m/z

Class 1: Ca-rich (Ca + Ca-oxides)

23

0 20 40 60 80 100 120 140 160 180 200 220 240 260

Ca2O2

Ca2O

UO2

UO

U

CaK

AlNa

inte

nsity

m/z

CaO

Co

Ba

Single particle spectrumSum of single particle spectra









Analyses of

► impurities ► age determinations ► average isotopic compositions:

enrichments of 4.1% and 16.8%

were made before the SIMS measurements.

Two forensics samples rich in uranium particles:

U-235 enrichment at bulk and at microscopic level?

Minor uranium isotopes?


Case 1

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

0.045

0.050

3.0 3.5 4.0 4.5 5.0

235 atom %

234

atom

%

Case 1 Case 1

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

0.045

0.050

3.0 3.5 4.0 4.5 5.0

235 atom %

236

atom

%

Case 1

U-235 atom%

U-2

34 a

tom

%

U-2

36 a

tom

%3.5 4.54.0

U-235 atom%3.5 4.54.0

Particle data: ► Powder mixture of at least two materials with 3.7% and 4.4% enrichment (234)► Each material results from the mixing of fresh and reprocessed material (236)

4.1


Case 2

0.000

0.020

0.040

0.060

0.080

0.100

0.120

0.140

0.160

0.180

0.0 5.0 10.0 15.0 20.0 25.0

235 atom %

234

atom

%

Case 2 Case 2

0.000

0.020

0.040

0.060

0.080

0.100

0.120

0.140

0.160

0.180

0.0 5.0 10.0 15.0 20.0 25.0

235 atom %23

6 at

om %

Case 2

U-235 atom% U-235 atom%

U-2

34 a

tom

%

U-2

36 a

tom

%5.0 20.015.010.0 5.0 20.015.010.0

16.8

► Typical isotopic signature of material from an enrichment facilitywith feed material containing reprocessed uranium (U-236).


0.000

0.005

0.010

0.015

0.020

0.025

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

235 atom %

236

atom

%

In spent fuel, U-236 increases with burn-up, i.e., decreasing U-235.

U-2

36 a

tom

%

1.0 3.0U-235 atom%


Are the U-236 results correct?Reprocessed material?

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.10

0.0 1.0 2.0 3.0 4.0 5.0 6.0

235 atom %

236

atom

%

IMS 4F

U-235 atom%

U-2

36 a

tom

%

1.0 6.0

M / ∆ M ≈ 300

No, the U-236 data are mainly background, molec. interferences!

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.10

0.0 1.0 2.0 3.0 4.0 5.0 6.0

235 atom %23

6 at

om %

IMS 1270

U-235 atom%U

-236

ato

m%

1.0 6.0

M / ∆ M ≈ 3000

Drawback of the present SIMS approach: low mass resolution, i.e., problems with molecular interferences in particular for samples with a large matrix component


Higher ion yield from an increase in transmission and detection efficiency => Smaller particles can be analysed=> Better ability to find undeclared activities

Improvements of SIMS particle analysis for Safeguards

Faster screening of material: The improved mass resolution “accepts” onlyuranium events and rejects interferences from molecular isobars=> Better ability to find undeclared activities

Increase the mass resolution from about 300 (“normal” SIMS)to about 3000 (larger bending radius in magnetic field)

=> Background suppression (molecular interferences PbAl, PbSi, …) for theminor uranium isotopes


Detailed evaluation of high-resolution SIMS

Y. Ranebo et al.” Improved isotopic SIMS measurements of uranium particles for nuclear safeguard purposes”, J. Anal. At. Spectrom., 2009, 24, 277 - 287

A report was delivered in February 2009 to the IAEA on the support program task EC A 01777; ”Evaluation of Ultra-High Sensitivity Secondary Ion Mass Spectrometry for Environmental Samples”.

High-quality isotopic data combined with detection speed.

Timely analyses are an important factorfor early detection of possible HEU production at enrichment facilities.


Joint project between JRC and Euratom to strengthen measurements of microparticles with nuclear material:• Large-Geometry SIMS laboratory, launched end of 2009.

• Verification of declared nuclear activities (Euratom).

• Support to IAEA via the European Commission Support Program (detection of undeclared activities).


Summary / Outlook

A strong nuclear nonproliferation regime is vital for the application of nuclear technology to prevent

► clandestine production of fissile material

► diversion of fissile material from the civil fuel cycle

Effective safeguards and nonproliferation will continue to requirecutting edge and highly sensitive detection techniques for nuclear material

Documents

How To Find the Needle in a Hay Stack: Tracing the History ... · interest. A classic “needle in the haystack” problem performed under strict time pressure. • To make precise