SLAC Measurement Protocols for Unrestricted Release of Metals and Concrete

SLAC Measurement Protocols for Unrestricted Release of Metals and Concrete

James Liu, Jim Allan, Sayed Rokni, Amanda SabourovRadiation Protection Department

SLAC National Accelerator Laboratory

DOE Accelerator Safety Workshop,August 17-19, 2010, SLAC, CA

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Summary of SLAC Measurement ProtocolsSummary of SLAC Measurement Protocols

• Purpose: Unrestricted release of metals and concrete• Release Criterion: Measurements are Indistinguishable

from Background (IFB), i.e., non-radioactive materials are not subject to regulatory controls and can have unrestricted release

• Measurement Methods: Use field instruments and surface survey techniques (with sufficient sensitivities) in an ambient environment with acceptable background– Volumetric radioactivity and surface contamination

• Technical Basis for Potential Volumetric Radioactivity: – Process knowledge for volumetric activation based on theoretical

evaluation and measurements– Principles of “Surface Maximum “and “Proxy Radioisotopes”– Detection Limits (MDAs) for radioisotopes of interest ≤ ANSI

N13.12 Screening Levels (SLs)– Bounding conditions for applicability

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NotesNotes

• SLAC measurement protocol for volumetric radioactivity:– Release criterion of IFB (specific activities for natural

radioisotopes, e.g., thorium and 40K, are 1-10 pCi/g)– Can also be used for higher release criteria, e.g., EU

Clearance Levels, ANSI N13.12 Screening Levels, or DOE Authorized Limits, for release of slightly radioactive materials.

– Presented as an example of possible methods and it is not to form the measurement bounding conditions.

• SLAC measurement protocol for surface contamination is the same as those commonly used in nuclear facilities, which have detection capabilities satisfying DOE Order 5400.5 Authorized Limits.

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Activation Characteristics in Electron AcceleratorsActivation Characteristics in Electron Accelerators

• Radioisotopes with Z or A lower than the parent isotopes can be produced, but no alpha emitters

• For off-site release purpose, most abundant radionuclides are those with long half-lives on the order of the beam irradiation time (about 1 to 10 years)

• Induced activity profile in an object is volumetric and the maximum activity is at the surface that faces the beam loss point (this justifies the surface measurements)

• Radioisotopes that are hard to measure are in general accompanied by “proxy” radioisotopes that can be measured (this justifies measurements for proxy radioisotopes, instead of measurements for all potential radioisotopes that can be produced)

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Radioisotopes of Interest in Metals and ConcreteRadioisotopes of Interest in Metals and Concrete

Material Radionuclide Half-life

Carbon steel (Fe, C) &Cast iron (Fe, C, Si, Mn)

22Na (proxy) 2.6 y54Mn (proxy) 312 d55Fe (5.9 keV x-ray) 2.73 y57Co 272 d

Aluminum 22Na (proxy) 2.6 y

Copper 55Fe (5.9 keV x-ray) 2.73 y57Co 272 d60Co (proxy) 5.26 y

Concrete 3H (pure beta) 12.3 y22Na (proxy) 2.6 y

54Mn (proxy) 312 d55Fe (5.9 keV x-ray) 2.73 y57Co 272 d60Co 5.26 y152Eu, 154Eu 13.5 y, 8.59 y

Proxy radioisotopes (22Na,

54Mn, 60Co), which emit high-energy and high-intensity gamma rays

10 Sv/y ANSI N13.12Screening Level (SL):22Na, 54Mn, 60Co: 30 pCi/g55Fe, 3H: 3000 pCi/g (100 Bq/g)

Detection Limit requirement:∑i (MDAi / SLi) 1

Radioisotopes with long half-lives are of interest.

Hard-to-measure radioisotopes (55Fe, 3H), which emit only low-energy X rays or beta rays.

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Hard-to-Measure and Proxy Radioisotopes for BaBarHard-to-Measure and Proxy Radioisotopes for BaBar

Radioisotope Half-lifeFLUKA-Calculated Specific Activity in pCi/g (% of total)

1 year 2 years 5 years

60Co (proxy) 5.3 y 1.0×10-6 (22%) 8.9×10-7 (27%) 6.0×10-7 (38%)

57Co 272 d 9.4×10-8 (2%) 3.7×10-8 (1.1%) 2.3×10-9 (0.1%)

55Fe 2.7 y 2.4×10-6 (53%) 1.9×10-6 (57%) 8.8×10-7 (55%)

54Mn (proxy) 313 d 6.5×10-7 (14%) 2.9×10-7 (9%) 2.5×10-8 (1.6%)

49V 338 d 2.7×10-7 (6%) 1.3×10-7 (4%) 1.4×10-8 (0.9%)

3H 12.3 y 6.9×10-8 (1.5%) 6.5×10-8 (2%) 5.5×10-8 (3.4%)

Remaining — 2.3×10-8 (0.5%) 1.0×10-8 (0.3%) 6.1×10-9 (0.4%)

Radioactivity in the BaBar IFR forward steel plug at three decay times

(SA/SL) for 55Fe is much less than (SA/SL) for 60Co

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Examples of Measured Nuclides in MetalsExamples of Measured Nuclides in Metals

Item No.Component

(Material) 1Radioisotope

Dose Rate(mR/h)

Activity 2

(pCi/g)Activity Ratio

to Co-60 3

ANSIN13.12 SL

(pCi/g)

090826-002

Al piece (Al)Co-60 0.03 42 1 30

Na-22 0.03 45 1.4 30

090826-006

Iron Sheet (Fe)Co-60 0.02 30 1 30

Na-22 0.02 32 0.04 30

070703-001

34-ft beam pipe (SS) Co-60 0.04 64 1 30

090921-002

Dump (Cu, SS) Co-60 0.1 76 1 30

090904-001

Iron plates/blocks (Fe)Co-60 0.4 293 1 30

Mn-54 0.4 1092 2 30

080918-001

Ballast (Fe, Cu)

Co-60 0.02 46 1 30

Mn-54 0.02 149 1.3 30

Na-22 0.02 50 0.3 30

Zn-65 0.02 222 0.2 30

1. All items were identified as radioactive and have been processed as radioactive waste.2. Conservatively calculated assuming the dose was coming from a single radioisotope. 3. Determined using field gamma spectroscopy.

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Radioactivity Profile in Activated ConcreteRadioactivity Profile in Activated Concrete

• Volumetric activation of concrete gives the maximum activity near the surface which faces the beam loss point

• Activity profile as a function of depth in concrete:– Photoneutron products such as 55Fe follow the

bremsstrahlung photon attenuation profile (1/1000 reduction per meter),

– Spallation products such as 3H and 22Na follow the high-energy neutron attenuation profile (1/10 reduction per meter),

– Thermal-neutron-capture products such as 60Co and 152Eu also follow the high-energy neutron attenuation profile (1/10 reduction per meter), but their magnitudes depend on Co and Eu trace elements

FLUKA-calculated Activity Profiles in Concrete WallFLUKA-calculated Activity Profiles in Concrete Wall

Depth (cm)

Act

ivit

y (B

q/g/

W)

• Cylindrical concrete tunnel• 10-year irradiation and 1-year decay• Calculated profiles agree with KEK measurements

0 50 10010-6

10-5

10-4

10-3

10-2Ee = 25 MeV

55Fe 22Na 57Co 58Co 54Mn

0 50 10010-6

10-5

10-4

10-3

10-2Ee = 1 GeV 55Fe

3H 22Na 54Mn 57Co

0 50 10010-6

10-5

10-4

10-3

10-2Ee = 100 MeV

55Fe 22Na 57Co 54Mn 3H

0 50 10010-6

10-5

10-4

10-3

10-2Ee = 10 GeV 55Fe

3H 57Co 22Na 54Mn

Surface Maximum

Photonuclear

1/1000 in 1-m

55Fe / 22Na 10

3H / 22Na 2

Spallation

1/10 in 1-m 55Fe / 22Na 2

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FLUKA-calculated Activity Profiles in Concrete WallFLUKA-calculated Activity Profiles in Concrete Wall

0 50 10010-6

10-5

10-4

10-3

10-2 Ee= 25MeV

55Fe 22Na 3H 54Mn 57Co

0 50 10010-6

10-5

10-4

10-3

10-2Ee= 100MeV

55Fe 22Na 3H 54Mn 59Fe

0 50 10010-6

10-5

10-4

10-3

10-2Ee= 1 GeV 3H

55Fe 22Na 60Co 54Mn

0 50 10010-6

10-5

10-4

10-3

10-2 Ee= 10 GeV 55Fe 3H 22Na 54Mn 57Co

Depth (cm)

Depth (cm)Depth (cm)

Depth (cm)

55Fe / 22Na 10

3H / 22Na 5

10-year irradiation and 5-year decay

Act

ivit

y (B

q/g/

W)

55Fe / 22Na 2

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Examples of Measured Nuclides in ConcreteExamples of Measured Nuclides in Concrete

Item # Description RadioisotopeActivity(pCi/g)

ANSI SL(pCi/g)

SL Fraction Notes

S02521FFTB CoreSample C-3

Co-60 26 30

2.0 Easily Detectable

Fe-59 6 300

Mn-54 14 30

Na-22 16 30

Sc-46 43 300

Total 107 0.2 mR/h

S03232

ConcreteSample

from PEP-II IR-10 Tune-up

Dump Wall

Zn-65 1 30

0.6 Detectable

Co-58 0.2 30

Co-60 9 30

Eu-152 3 30

Mn-54 1 30

Na-22 3 30

Total 18 0.02 mR/h

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Hard-to-Measure and Proxy Radioisotopes in ConcreteHard-to-Measure and Proxy Radioisotopes in Concrete

• The specific radioactivity for hard-to-measure radioisotopes (55Fe and 3H) can be higher than the main proxy radioisotope (22Na).

• Bounding condition for applicability of proxy radioisotope approach is ~20 years decay time for the activity ratio of 3H-3/22Na to exceed their ANSI Screening Level ratio of 100. One solution is to conduct surface swipe or collect sample for 3H counting.

• If Co and Eu trace elements exist, the radioisotopes of 60Co and 152Eu can serve as better proxy radioisotopes for 3H for concrete blocks with very long decay times (tens of years).

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SLAC Field Survey InstrumentsSLAC Field Survey Instruments

Ludlum Model 18 with 44-2 detector

TBM P15

Ludlum Model 2241 with both a 44-2 detector (1” NaI) and a GM pancake

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SLAC Volumetric Radioactivity MeasurementsSLAC Volumetric Radioactivity Measurements

Instrument Field Survey Technique Procedures& TBD

Notes

Ludlum 2241 or 18

Meterwith44-2

Detector(1” NaI)

1. Background < 600 cpm

2. Scan surface area or conduct direct fixed point measurements

3. If there are inaccessible surfaces, use process knowledge and/or disassemble item to gain access to all surfaces.

4. If net < 120 cpm (at BKG of 600 cpm), the item is not radioactive

1) FO-0182) FO-0423) SLAC-I-760-2A26J-017 and -

028

Conservativeefficiency & MDA

calculated for proxy

radioisotopes (related to

point-source calibration)

MDA 3 pCi/g(22Na, 54Mn, 60Co)

MDA 25 pCi/g (57Co)

ANSI N13.12Screening Levels (SL):1. High dose beta-gamma

emitters (22Na, 54Mn,

60Co): 30 pCi/g2. General beta-gamma

emitters (57Co): 300 pCi/g

1) ANSI N13.12 SL values were based on 10 Sv/y dose risk2) ∑i (MDAi / SLi) 1

R

Z

MDA Calculations Using MCNPMDA Calculations Using MCNP

Metal with Potential Volumetric Activation

Detector near Object Surface

MDA = 4 B / η

Sensitivity [η in cpm/(pCi/g)] for various volumetric distributions for proxy radioisotopes in metals were calculated using MCNP

MDA for the uniform case [η = 162 cpm/(pCi/g)] is most conservative 0

1

2

3

200 300 400 500 600 700 800

fastslow

MDA (pCi/g)

Background count rate (cpm)

Sensitivity; 162 cpm/(pCi/g)MDA=4

B

Material; FeSource ; Co-60

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SLAC Surface Contamination MeasurementsSLAC Surface Contamination Measurements

Instrument Protocol Procedures Notes

Fixed Contamination

GM Pancake

1. For beta-gamma isotopes 2. Background < 100 cpm 3. Scan item 2”/s within ½” of

surface4. Scan entire surface area5. If net < 100 cpm, the item is

not radioactive

FO-018FO-032FO-031

SLAC-I-760-2A26J-024 and -027

Maximum MDA = 1000 dpm/100 cm2

DOE 5400.5 Authorized Limit (AL):beta-gamma emitters= 5,000 dpm/100 cm2

Loose Contamination

GM Pancake

1. For beta-gamma isotopes2. Background < 100 cpm3. Swipe 100 cm2 area4. Count swipe for 20 s5. If net < 100 cpm, the item is

not radioactive

FO-018FO-032FO-031

SLAC-I-760-2A26J-024 and -027

Maximum MDA = 1000 dpm/100 cm2

DOE 5400.5 Authorized Limit (AL):beta-gamma emitters= 1,000 dpm/100 cm2

1) ∑i (MDAi / ALi) 1

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Graded Approach for Measurement ProcessGraded Approach for Measurement Process

• Graded measurement approach based on process knowledge

• General Process Knowledge:– Physics of radioisotope production based on characteristics of

accelerator, beam parameters, and materials

• Facility-Specific Process Knowledge:– Accelerator and facility operation and beam loss information

• Graded Measurement Approach:– Follow MARSSIM and MARSAME guidance– Identification of Areas of Interest (AOIs) or Activities of Interest– Selection of locations of a facility, surfaces of a component, or

areas of a surface to be surveyed– Scanning versus discrete point measurements

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Additional Measurements When WarrantedAdditional Measurements When Warranted

• Samples for Radioanalysis Laboratory measurements– Independent verification when process knowledge is

not known, e.g.,• Field gamma spectrometry• Environmental measurement protocol using HPGe

with detection limits at least ten times lower than field measurements (0.1 pCi/g for proxy isotopes and 10 pCi/g for 3H)

• Surface swipe for 3H and 55Fe LSC analysis• Portal Gate Monitoring:

– Detection limits about 1 Ci for proxy isotopes– Useful to supplement the field measurements

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Record Management and Reporting Record Management and Reporting

• Release Records– Release decisions (e.g., no potential reuse), authorization, and

process knowledge, if any (conditions of accelerator, facility and/or materials)

– Survey results

• Large items are individually identified, surveyed, and recorded.

• Small items are individually surveyed, and collectively identified and recorded.

• Instruments, background signals, surveyor, date/time of survey

• Photos may be used.

– Survey and measurement procedures

– Training records for survey technicians

• Reporting– ASER

– Amounts and types of materials released

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How Low the MDA Should Be?How Low the MDA Should Be?

• Clearance Levels or Authorized Limits (unrestricted release of slightly radioactive materials)– A “de minis” dose criterion of 1 mrem/y– 30 pCi/g for proxy isotopes– 2000-h/yr external exposure scenario for proxy isotopes– Dose rate at 30 cm from the object due to proxy

radioisotopes is 0.5 µR/h, equivalent to 5 µR/h at 3 cm.• IFB (unrestricted release of non-radioactive materials)

– 1 to 10 pCi/g for natural isotopes, e.g., thorium and 40K– Field survey MDA ~ 3 pCi/g for proxy isotopes– Field gamma spectrometry MDA ~1 pCi/g for proxy

isotopes• Radioanalysis Lab Environmental Measurement Protocol

– 0.01 to 0.1 pCi/g for natural and proxy isotopes

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How low the MDA can be?How low the MDA can be?

• Common field instruments (e.g., 1 to 3 inch NaI or plastic scintillator) can detect 2-3 µR/h in an ambient background of 10-15 µR/h.

• Specific Gamma-ray Constant for 22Na is 3.6E-4 mSv/h/MBq at 1 m. Therefore, 1340 pCi of a 22Na point source gives 2 µR/h at 3 cm

• The calculated MDA for SLAC direct scanning method at 1” from the surface of a volumetric activated object is 3 pCi/g for 22Na.

• This amounts to a mass of 1340/3 = 440 g or 60 cm3 for iron.

• This is consistent with value and the common instruments’ detection limits.

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Summary of SLAC Measurement ProtocolsSummary of SLAC Measurement Protocols

• Purpose: Unrestricted release of metals and concrete• Release Criterion: Measurements are Indistinguishable

from Background (IFB), i.e., non-radioactive materials are not subject to regulatory controls and can have unrestricted release

• Measurement Methods: Use field instruments and surface survey techniques (with sufficient sensitivities) in an ambient environment with acceptable background– Volumetric radioactivity and surface contamination

• Technical Basis for Potential Volumetric Radioactivity: – Process knowledge for volumetric activation based on theoretical

evaluation and measurements– Principles of “Surface Maximum “and “Proxy Radioisotopes”– Detection Limits (MDAs) for radioisotopes of interest ≤ ANSI

N13.12 Screening Levels (SLs)– Bounding conditions for applicability

Electron Beam Loss

Potential Activation in Electron Accelerators Tunnel

High-Energy and Low-Energy Neutrons

Bremsstrahlung Photons

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• Spallation• Photonuclear• (n,)

FLUKA Calculations of Induced Activity in BaBar DetectorFLUKA Calculations of Induced Activity in BaBar Detector24

Three-Floor-High,

Thousands Pieces

FLUKA is a Monte Carlo code that can calculate induced radioactivity in a 3-D geometry in accelerator facilities, well benchmarked by SLAC and CERN experiments

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Calculated Volumetric Radioactivity Profile in BaBarCalculated Volumetric Radioactivity Profile in BaBar

Notice how the radioactivity profile of each BaBar component has its maximum on the side that faces the source (i.e., e+ and e- collision point inside BaBar)

SALC RP Note 09-04, 2009

10-3

10-2

10-1

100

101

0 10 20 30 40 50

Act

ivit

y (B

q/g)

Depth (cm)

10-3

10-2

10-1

100

101

0 10 20 30 40 50

Act

ivit

y (B

q/g)

Depth (cm)

10-3

10-2

10-1

100

101

0 10 20 30 40 50

Act

ivit

y (B

q/g)

Depth (cm)

H-3

Co-60

Eu-152

Cs-134

Mn-54

Na-22

45 MeV 220 MeV 1.3 GeV

Measured Activity Depth Profiles in Concrete

Measurements by Masumoto et al., of KEK at three electron accelerators “Evaluation of radioactivity induced in the accelerator building and its application to decontamination work” in the Journal of Radio-analytical and Nuclear Chemistry, 255:3, 2003.

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