verification measurements of alpha active waste

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

5th International Summer School JRC, Ispra, 9-13 September 2013

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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.

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Motivation for special attention to alpha active nuclear waste: - particles have high “relative biological effectiveness” (WR): 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. 233U, 235U, all Pu isotopes, 241Am …

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Italian regulation for radioactive concentrations in waste items Guida Tecnica no. 26 Example: 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)

* 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)

average, all items

limit, single item

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Example: -activity of standard Pu material (medium burn-up) 1 gram of CBNM Pu61, PuO2 reference standard decay and activity calculation: Nucleonica

238Pu 11.969 7.59E+09 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

234U 2.26 5.20E+05

237Np 1.84 4.79E+04

236U 0.71 1.68E+03

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Example: -activity of low-enriched uranium (4.46% 235U) 1 gram of U3O8 CBNM references standard date of separation of daughter products: 01 June 1979 decay and activity calculation: Nucleonica

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

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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

Example: Max content of standard Pu in conditioned waste, Cat-II

- specific -activity (Pu sample): 1.75E+10 Bq/g

- Cat-II limit emitters T½ >5 years: 3.7 kBq/g

- standard 220-litre container, concrete: 5.00E+05 g

Max. Pu mass: 106 mg

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Sources of neutrons emission in oxide samples • Spontaneous fission • (α, n) reactions on oxygen, beryllium, boron • Neutron induced fission (self-multiplication)

Neutron emission in alpha active waste

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Neutron sources

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Decay modes of important actinides for NDA methods

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Spontaneous fission neutrons

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Neutron emission and detection - time sequence

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Singlet detection

Correlated and un-correlated multiplets

Doublet detection

Triplet detection

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The measured signal frequency distribution

The normalized factorial moments

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Singlets, doublets and triplets

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Relationship between measured quantities and physical parameters

Correlated multiplets

where: FS = sample spontaneous fission rate, = detection efficiency, = ratio of (,n) neutrons to spontaneous fission neutrons, M = self-multiplication factor

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Point model requirements:

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Fundamental mode decay of thermal neutrons in

detector/moderator assembly single exponential decay: 3He in narrow HDPE modules, Cd on all

surfaces Constant neutron detection probability over sample volume and

neutron energy Detector modules in 4p geometry, detectors in multiple rows Constant fast fission probability over sample volume and

neutron energy

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Passive neutron counting for alpha active

waste

JRC Drum Monitor design

220-litre waste drum

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waste



Vertical 3He detectors

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waste




Horizontal 3He detectors

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waste





Amplifier junction boxes

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waste






Polyethylene moderator

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waste






Polyethylene moderator

External neutron shield

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waste

• 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 3He detectors, 4 bar - 4p detector geometry, - substantial neutron shield, 240 mm HDPE

JRC Drum Monitor, design features

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Passive neutron counting for alpha active waste

JRC Drum Monitor

Multiplicity counting (singlets, doublets, triplets): Mass assay of small amounts, examples - Low-density matrix: 49 mg PuO2, 11.3 mg 240Pu, 3-hour measurement INCC: mass diff. 3.5% ± 1.05% Multiplication 1.008 ± 0.002 Alpha 0.48 ± 0.02 - Concrete matrix (450 kg): 565 mg PuO2, 131 mg 240Pu, 3-hour measurement INCC: mass diff. 12.5% ± 5.05% Efficiency 0.18 ± 0.07 Alpha 0.66 ± 0.12

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Passive neutron counting for alpha active waste

JRC Drum Monitor,

detection limit, minimum detectable mass, ….

Neutron background characteristics, 220-litre drums:

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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)

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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


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Exponential time response function of thermal neutrons:

• maximum thermal flux @ 260 μs after 14-MeV burst

• thermal neutron lifetime: 1.05±0.02 milliseconds

0 1 2 3 4 50.0

0.2

0.4

0.6

0.8

1.0

Norm

ali

zed

Cou

nts

Time After Trigger [ms]

0 1 2 3 4 5 6 7 810

-3

10-2

10-1

100

measurements

single exponential fit

Norm

ali

zed

Cou

nts

Time After Trigger [ms]

Thermal neutron flux dynamics


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Mass determination by thermal neutron induced fission

0 2 4 6 8

100

101

102

103

104

105

106

Co

un

ts p

er

ch

an

ne

l

Time after (D-T) trigger /ms

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

235U mass range: 0.5 – 7.5 g

Meas. time: 10 min

14-MeV rate: 107 /s

Pulse rate: 100 Hz

Detectors: 3-He

Detection of prompt fission neutrons - Differential Die-Away technique (DDA) CBNM U3O8 standards

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0 1 2 3 4 5 6 7 8

0.0

2.0x105

4.0x105

6.0x105

8.0x105

1.0x106

Ne

t in

teg

ral co

un

ts

Mass 235

U /g

CBNM low enriched U sources

2nd order poly fit

235U mass range: 0.5 – 7.5 g

Meas. time: 10 min

14-MeV n rate: 107 /s

Pulse rate: 100 Hz

Detectors: 3-He

Detection of prompt fission neutrons - Differential Die-Away technique (DDA) CBNM U3O8 standards Integral range: 700 – 4700 s


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0 200 400 600 800 1000

1.2x105

1.4x105

1.6x105

1.8x105

2.0x105

2.2x105

2.4x105

2.6x105

Ne

t in

teg

ral co

un

ts

Mass 239

Pu /mg

PuGa source, 93% 239

Pu

linear fit

239Pu mass range: 8.6 – 846

mg

Meas. time: 10 min

14-MeV n rate: 107 /s

Pulse rate: 100 Hz

Detectors: 3-He

Detection of prompt fission neutrons - Differential Die-Away technique (DDA) PuGa standards Integral range: 700 – 4700 s


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Detection of prompt fission neutrons - Differential Die-Away technique (DDA) Problems: • Thermal neutron flux depression in sample • Attenuation of thermal neutron flux in matrix materials Our research: • DDA technique combined with neutron correlation technique: Single events: Double (pair) events:

i2(1) (2) 22fm(i),m(i)ABe

i1(1) (1) 11fm(i)m(i)ABe

0I fI,()I

AB(T)G (,,)

M


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Thank you!

Bent Pedersen Joint Research Centre Institute for Transuranium Elements Nuclear Security Unit 21027 Ispra (VA), Italy [email protected]

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verification measurements of alpha active waste

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