Verification measurements of alpha active waste Bent Pedersen Nuclear Security Unit Institute for Transuranium Elements (ITU), JRC Operational Issues in Radioactive Waste Management and Nuclear Decommissioning 6 th International Summer School JRC, Ispra, 8-12 September 2014 1
Characterization methods and systems for radioactive/nuclear waste Integral systems based on gamma spectroscopy: - HPGe detectors with interpretation software (e.g. ISOCS), - Segmented gamma scanning, - Tomographic gamma scanning with transmission source Typical applications: Medical isotopes, industrial isotopes, fission products, neutron activated materials, free release/clearance Integral systems based on neutron detection: Passive waste assay systems for large volumes Active interrogation: - LINAC photon interactions: (, n), (, f) - neutron interrogation: (n, f) Typical applications (actinides, TRU waste, LLW): process waste from nuclear fuel cycle facilities: reprocessing, fuel fabrication, spent fuel storage, etc. 2
Motivation for special attention to alpha active nuclear waste: - particles have high relative biological effectiveness (W R ): isolate from biosphere - Long half-lives requires safe containment for long time: conditioning of the waste, safe storage facilities (high price) - Nuclear facilities are required to maintain full accountancy of nuclear material inventory - Many actinides are included under international regulation: nuclear safeguards & non-proliferation e.g. 233 U, 235 U, all Pu isotopes, 241 Am 3
Italian regulation for radioactive concentrations in waste items Guida Tecnica no. 26 Example: LLW, category 2, conditioned waste TABELLA 1 LIMITI DI CONCENTRAZIONE PER RIFIUTI RADIOATTIVI DELLA SECONDA CATEGORIA CONDIZIONATI AI FINI DELLO SMALTIMENTO RADIONUCLIDI CONCENTRAZIONE emettitori t½ > 5 anni * 370 Bq/g (10 nci/g) / emettitori t½ > 100 anni * 370 Bq/g (10 nci/g) / emettitori t½ > 100 anni in metalli attivati 3.7 K Bq/g (100 nci/g) / emettitori 5 < t½ 100 37 K Bq/g (1 µci/g) 137Cs e 90Sr 3.7 M Bq/g (100 µci/g) 60Co 37 M Bq/g (1 mci/g) 3H 1.85 M Bq/g (50 µci/g) 241Pu 13 K Bq/g (350 nci/g) 242Cm 74 K Bq/g (2 µci/g) Radionuclidi t½ 5 anni 37 M Bq/g (1 mci/g) average, all items * i valori sono da intendersi come valori medi riferiti alla totalità dei rifiuti contenuti nel deposito di smaltimento, tenendo presente che il valore limite per ciascun manufatto non può superare 3.7 KBq/g (100 nci/g) limit, single item 4
Example: -activity of standard Pu material (medium burn-up) 1 gram of CBNM Pu61, PuO 2 reference standard 20 June 1986 today Isotope mass Alpha activity Isotope mass Alpha activity [mg] [Bq] [mg] [Bq] 238Pu 11.969 7.59E+09 no 1 9.68 6.13E+09 239Pu 625.255 1.44E+09 625.00 1.43E+09 240Pu 254.058 2.14E+09 254.00 2.13E+09 241Pu 66.793 6.30E+06 18.10 1.71E+06 242Pu 41.925 6.14E+06 42.00 6.14E+06 241Am 14.452 1.83E+09 61.30 7.77E+09 Total Pu mass 1000.00 948.78 no 1 Total alpha 1.30E+10 1.75E+10 234U 2.26 5.20E+05 237Np 1.84 4.79E+04 236U 0.71 1.68E+03 decay calculation: Nucleonica 5
Example: -activity of low-enriched uranium (4.46% 235 U) 1 gram of U 3 O 8 CBNM references standard date of separation of daughter products: 01 June 1979 01 June 1979 today Isotope mass Alpha activity Isotope mass Alpha activity [mg] [Bq] [mg] [Bq] 235U 44.6 1.18E+04 44.6 1.18E+04 238U 955.4 3.56E+03 955.4 3.56E+03 231Pa 2.48E+00 234U 1.10E+00 227Ac 1.30E-02 Total 1000.00 1.54E+04 1000.0 1.54E+04 decay calculation: Nucleonica 6
Example: Max content of standard Pu in conditioned waste, Cat-II - specific -activity (Pu sample): 1.75E+10 Bq/g - Cat-II limit, emitters T ½ >5 years: 3.7 kbq/g - standard 220-litre container, concrete: 5.00E+05 g Max. Pu mass: 106 mg Example: Max content of low-enriched U in conditioned waste, Cat-II - specific -activity (U sample): 1.54E+04 Bq/g - Cat-II limit emitters T½ >5 years: 370 Bq/g - standard 220-litre container, concrete: 5.00E+05 g Max. U mass: 12 kg 7
Neutron emission in alpha active waste Sources of neutrons emission in oxide samples Spontaneous fission (α, n) reactions on oxygen, beryllium, boron Neutron induced fission (self-multiplication)
Decay modes of important actinides for NDA methods 9
Neutron sources, oxide fuel
neutron emission Spontaneous fission neutrons
Neutron emission and detection - time sequence 12
Singlet detection Correlated and un-correlated multiplets Triplet detection Doublet detection
The measured signal frequency distribution The normalized factorial moments
Relationship between measured quantities and physical parameters Correlated multiplets where: F S = spontaneous fission rate proportional to fissile mass, = detection efficiency, = ratio of (,n) neutrons to spontaneous fission neutrons M = self-multiplication factor
Point model: requirements to the detector design
Neutron detection in 3 He proportional counters Good features: high n detection efficiency good /n discrimination long term stability Bad features: very high price
Passive neutron counting for alpha active waste 18 JRC Drum Monitor design 220-litre waste drum
Passive neutron counting for alpha active waste 19 JRC Drum Monitor design 220-litre waste drum Vertical 3 He detectors
Passive neutron counting for alpha active waste 20 JRC Drum Monitor design 220-litre waste drum Vertical 3 He detectors Horizontal 3 He detectors
Passive neutron counting for alpha active waste 21 JRC Drum Monitor design 220-litre waste drum Vertical 3 He detectors Horizontal 3 He detectors Amplifier junction boxes
Passive neutron counting for alpha active waste 22 JRC Drum Monitor design 220-litre waste drum Vertical 3 He detectors Horizontal 3 He detectors Amplifier junction boxes Polyethylene moderator
Passive neutron counting for alpha active waste 23 JRC Drum Monitor design 220-litre waste drum Vertical 3 He detectors Horizontal 3 He detectors Amplifier junction boxes Polyethylene moderator External neutron shield
Passive neutron counting for alpha active waste 24 JRC Drum Monitor, design features Operated by Euratom Safeguards - passive neutron counting of 220-litre condition/un-conditioned waste - Pu verification campaigns in European facilities - JSR-14 + INCC analysis Characteristics: - max. 1,000 kg drums - CE certified (March/April 2013) - fission neutron efficiency 32% - die-away time 54 microseconds - 148 3 He detectors, 4 bar - 4 detector geometry, - substantial neutron shield, 240 mm HDPE
Passive neutron counting for alpha active waste 25 JRC Drum Monitor, measurement characteristics: Multiplicity counting (singles, doubles, triples): Mass assay, typical examples - Low-density matrix: 49 mg PuO 2, 11.3 mg 240 Pu, 3-hour measurement INCC: mass diff. 3.5% ± 1.05% Multiplication 1.008 ± 0.002 Alpha 0.48 ± 0.02 - Concrete matrix (500 kg): 565 mg PuO 2, 131 mg 240 Pu, 3-hour measurement INCC: mass diff. 12.5% ± 5.05% Efficiency 0.18 ± 0.07 Alpha 0.66 ± 0.12
Pulsed Neutron Interrogation Test Assembly - PUNITA Objective: Research in NDA methods and instrumentation for applications in nuclear safeguards and security Nuclear Safeguards: Mass determination of small quantities of fissile material Method: Differential Die-Away technique with neutron correlation analysis Applications: e.g. nuclear waste assay Nuclear Security: Detection of special nuclear material (SNM) in shielded containers. Method: detection of fission signatures Application: e.g. air cargo containers (ULDs) 26
Pulsed Neutron Interrogation Test Assembly - PUNITA Features sample cavity: 50 cm x 50 cm x 80 cm thick graphite linear on all six side fission neutron counters: He-3 in polyethylene low pressure, thermal flux monitors monitor for neutron generator output HPGe, LaBr3, scintillators in cavity side view top view
Pulsed Neutron Interrogation Test Assembly - PUNITA 14-MeV neutron generator: MF Physics Model A-211 neutron emission 2 10 8 /s, 10 6 /burst in 4π angle sealed, D-T mixed beam 300-500 hours life pulsing of ion source and acceleration voltage no emission between bursts neutron burst width: 10 µs burst repetition rate: 1 150 s -1 Thermo Fisher Scientific Corporation
Counts per channel Mass determination by thermal neutron induced fission 29 Detection of prompt fission neutrons - Differential Die-Away technique (DDA) CBNM U 3 O 8 standards 10 6 10 5 10 4 10 3 background CBNM 0.31% 235 U CBNM 0.71% 235 U CBNM 1.94% 235 U CBNM 2.95% 235 U CBNM 4.46% 235 U Thermal n in cavity 235 U mass range: 0.5 7.5 g Meas. time: 10 min 14-MeV rate: 10 7 /s Pulse rate: 100 Hz Detectors: 3-He 10 2 10 1 10 0 0 2 4 6 8 Time after (D-T) trigger /ms
Net integral counts Mass determination by thermal neutron induced fission 30 Detection of prompt fission neutrons - Differential Die-Away technique (DDA) PuGa standards, no matrix Integral range: 700 4700 s 2.6x10 5 2.4x10 5 2.2x10 5 PuGa source, 93% 239 Pu linear fit 2.0x10 5 1.8x10 5 1.6x10 5 239 Pu mass range: 8.6 846 mg Meas. time: 10 min 14-MeV rate: 10 7 /s Pulse rate: 100 Hz Detectors: 3-He 1.4x10 5 1.2x10 5 0 200 400 600 800 1000 Mass 239 Pu /mg
Mass determination by thermal neutron induced fission 31 Conclusions: Active and passive neutron mass assay as applied to -active waste characterization Passive neutron counting (passive drum monitor) Pu assay accuracy is good even in conditioned waste (10-30%) Can hardly verify nuclear waste down to LLW acceptance levels Active neutron counting (Differential Die-Away technique) At least 10x lower mass determination not as accurate as passive assay problems: thermal neutron flux depression in sample attenuation of thermal neutron flux in matrix materials more research needed!
Thank you! Bent Pedersen Joint Research Centre Institute for Transuranium Elements Nuclear Security Unit 21027 Ispra (VA), Italy bent.pedersen@jrc.ec.europa.eu