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

Transcription

1 San Diego, 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 Luetzenkirchen Institute for Transuranium Elements Joint Research Centre, European Commission Karlsruhe, Germany

2 San Diego, February 2010 AAAS Annual Meeting 2 Context of the presentation: Nuclear analytical measurements play a key role for the development of nuclear technology and for the assurance of its peaceful use The challenge is to measure uranium/plutonium for safeguards purposes from the very large quantities in reprocessing facilities down to microparticles as a record of nuclear activities

3 San Diego, February 2010 AAAS Annual Meeting 3 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 reprocessing analysis of particles of nuclear material as an example uranium-235 enrichment measurements Nuclear forensics - Analysis of seized nuclear material from illicit trafficking

4 San Diego, February 2010 AAAS Annual Meeting 4 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. Sampling of dust at a picture of ausing 1-µma nuclear facility uranium particle cotton swipe. (D. Simons, NIST) 7 x 10-8 Bq (2.6 x 10-12g)

5 San Diego, February 2010 AAAS Annual Meeting 5 Particle Analysis from environmental sampling 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 U 238 U U-235 SIMS image U-238 SIMS image Particle distribution. (Resolution 1050x and 3500x).

6 San Diego, February 2010 AAAS Annual Meeting 6 oxygen ion beam Secondary ion mass spectrometer (SIMS) uranium ions mass spectrometer particle with nuclear material detector

7 San Diego, February 2010 AAAS Annual Meeting 7 Tails: U-depleted Histogram Enrichment Plant A Number of Particles Feed: U-natural Normal Production Range Reactor Fuel U235 [mass%]

8 San Diego, February 2010 AAAS Annual Meeting 8 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-238 info on enrichment process U-236: half life 23.4 million years; abundance in nature practically zero, produced in nuclear reactors present in reprocessed feed material

9 San Diego, February 2010 AAAS Annual Meeting 9 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-238 info on enrichment process U-236: half life 23.4 million years; abundance in nature practically zero, produced in nuclear reactors present in reprocessed feed material

10 San Diego, February 2010 AAAS Annual Meeting 10 How to detect uranium particles in a matrix of ordinary material? What is their morphology? Coupling of SIMS with scanning electron microscopy (SEM) One of three particles found by SIMS (Field 18,21) Field 18,21 seen in the SEM

11 San Diego, February 2010 AAAS Annual Meeting 11 uranium backscatter mode Transfer between the two X-ray instruments spectra emitted SIMS and from SEM: various Particle search by SIMS (the parts 300-nm of particle the particle was not after found excitation by the SEM): by the electron beam 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.

12 San Diego, February 2010 AAAS Annual Meeting 12 Seized MOX powder 1994: SEM EDX Elements El. Diffr. in TEM Oxides PuO 2 platelets (80%) PuO 2 rods ( 5%) particle shape production facility U 3 O 8 hexagons (15%) x1000

13 San Diego, February 2010 AAAS Annual Meeting 13 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-238 info on enrichment process U-236: half life 23.4 million years; abundance in nature practically zero, produced in nuclear reactors present in reprocessed feed material

14 San Diego, February 2010 AAAS Annual Meeting 14 Age = the time elapsed since the last chemical processing (e.g. production, reprocessing, purification) MOX powder: Age in 1994 (years): alpha-decay Isotope ratio Platelets Rod-shaped 240 Pu/ 236 U 15.5 ± ± 0.3

15 San Diego, February 2010 AAAS Annual Meeting 15 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-238 info on enrichment process U-236: half life 23.4 million years; abundance in nature practically zero, produced in nuclear reactors present in reprocessed feed material

16 San Diego, February 2010 AAAS Annual Meeting 16 Trace elements: non-nuclear signatures for the characterisation of particles Single particle aerosol mass spectrometry for each particle analysed, the full mass spectrum is recorded test applicability to single particles from swipe samples 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)

17 San Diego, February 2010 AAAS Annual Meeting 17 1 µm uranium oxide particles of different enrichment U: 3% U-235: 3% U UO + UO 2 + U + UO + UO intensity (a.u.) U-235: U: 10% 10% 235 U UO + UO mass (m/z) Different enrichments can be distinguished (LEU vs. HEU) potential for detection of (undeclared) uranium enrichment activities

18 San Diego, February 2010 AAAS Annual Meeting 18 Classification of particles from swipes: Ca-oxide + Al, Ba heavy concrete uranium appears mainly in this class (3% of total) Single particle spectrum Sum of single particle spectra Class 1: Ca-rich (Ca + Ca-oxides) Na Al K Ca CaO 1,0 0, : Na 27: Al 39: K 40: Ca 56: CaO intensity Co Ca 2 O U UO intensity 0,6 0, : Ca 2 O 112: Ca 2 O 2 Ca 2 O 2 Ba UO 2 0, m/z 0, m/z

19 San Diego, February 2010 AAAS Annual Meeting 19 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-238 info on enrichment process U-236: half life 23.4 million years; abundance in nature practically zero, produced in nuclear reactors present in reprocessed feed material

20 San Diego, February 2010 AAAS Annual Meeting 20 Two forensics samples rich in uranium particles: U-235 enrichment at bulk and at microscopic level? Minor uranium isotopes? Analyses of impurities age determinations average isotopic compositions: enrichments of 4.1% and 16.8% were made before the SIMS measurements.

21 San Diego, February 2010 AAAS Annual Meeting Case Case 1 1 Case U-234 atom% % U-236 atom% 236 atom % atom % U-235 atom% atom % U-235 atom% 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)

22 San Diego, February 2010 AAAS Annual Meeting Case Case 2 2 Case U-234 atom% 234 % U-236 atom% 236 atom % atom % 235 atom % U-235 atom% U-235 atom% Typical isotopic signature of material from an enrichment facility with feed material containing reprocessed uranium (U-236).

23 San Diego, February 2010 AAAS Annual Meeting 23 In spent fuel, U-236 increases with burn-up, i.e., decreasing U % U-236 atom% U-235 atom% %

24 San Diego, February 2010 AAAS Annual Meeting Drawback of the present SIMS approach: low mass resolution, i.e., problems with molecular interferences in particular for samples with a large matrix component IMS 4F 0.10 IMS U-236 atom% 236 atom % M / M 300 U-236 atom% 236 atom % M / M atom % 6.0 U-235 atom% % U-235 atom% Are the U-236 results correct? Reprocessed material? No, the U-236 data are mainly background, molec. interferences!

25 San Diego, February 2010 AAAS Annual Meeting 25 Improvements of SIMS particle analysis for Safeguards 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 the minor uranium isotopes Faster screening of material: The improved mass resolution accepts only uranium events and rejects interferences from molecular isobars => Better ability to find undeclared activities Higher ion yield from an increase in transmission and detection efficiency => Smaller particles can be analysed => Better ability to find undeclared activities

26 San Diego, February 2010 AAAS Annual Meeting 26 Detailed evaluation of high-resolution SIMS High-quality isotopic data combined with detection speed. Timely analyses are an important factor for early detection of possible HEU production at enrichment facilities. 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. Y. Ranebo et al. Improved isotopic SIMS measurements of uranium particles for nuclear safeguard purposes, J. Anal. At. Spectrom., 2009, 24,

27 San Diego, February 2010 AAAS Annual Meeting 27 Joint project between JRC and Euratom to strengthen measurements of microparticles with nuclear material: Large-Geometry SIMS laboratory, launched end of Verification of declared nuclear activities (Euratom). Support to IAEA via the European Commission Support Program (detection of undeclared activities).

28 San Diego, February 2010 AAAS Annual Meeting 28 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 require cutting edge and highly sensitive detection techniques for nuclear material