Material Release Protocols Used
at Thomas Jefferson National Accelerator Facility
DOE Accelerator Safety Workshop
SLAC National Accelerator Laboratory
August, 2010
Keith Welch
Jefferson Lab
Radiation Control Department
Deputy Manager
Thomas Jefferson National Accelerator Facility
Jefferson Lab Facilities
CEBAF Accelerator
6 GeV, 1MW CW Electron Beam
Recirculating LINAC
Free Electron Laser
120 MeV, 1.2 MW CW Electron Beam
120 kW Energy Recovery LINAC
Approach to Clearance at JLab
• Monitoring for accelerator-related radioactivity is
significantly different than at a nuclear facility
– Especially at electron machines:
• Most activity is volumetric
• Surface contamination is minimal
• No approved action levels for the situation of primary concern
• Potentially impacted materials exit accelerator enclosures
daily – a practical approach is needed
– Use existing limits for surface activity where applicable
– For potential volumetric activity, base release on detectability
• Material released as “Indistinguishable from Background”
• Applies to all materials (including metals)
(We will focus here on field monitoring for volumetric activity)
Thomas Jefferson National Accelerator Facility
Approach to Clearance at JLab
• Determine by process knowledge/survey what areas can
be considered non-impacted
– Areas within beam enclosures with low luminosity
– Areas with energy below activation thresholds
• Categorize/evaluate material (by type and class)
–
–
–
–
Physical attributes, location relative to beam
Nuclides of interest
Some materials better suited for analytical assay
Can some classes be surveyed < 100% ?
• Determine type(s) of survey/analysis required for material
– Evaluate detection sensitivity
– Compare sensitivity to standards
(this should look familiar if you are acquainted with MARSSIM/MARSAME)
Thomas Jefferson National Accelerator Facility
Evolution of Jlab Release Protocols
• First technical basis ~ 1990
• Topic-specific technical bases for:
– Liquids (2006)
– Ion Exchange Resin (2008)
– Solids (2009)
– Process/policy document consolidates protocols and criteria (2010)
Latest revisions of current TBDs all reviewed by TJSO, several by HQ
• Current approach is consistent with:
– DOE requirements and guidance
– MARSSIM/MARSAME methodology
– ANSI/IAEA standards
Thomas Jefferson National Accelerator Facility
Release Protocols
• Implications of ‘IFB’ Protocols:
– “Detectable” must be defined
• For field surveys, detectability is in terms of instrument
response, not a quantitative activity assessment
• Instrument response should be modeled/assessed to
determine range of realistic MDC
– Null hypothesis not the same as for limit-based clearance
•
•
•
•
H0 – item surveyed has no radioactivity above bkg
To reject null hypothesis, activity must be detected
Action Level = 0 - indistinguishable from background
Discrimination Limit = Critical Value
(H0 approach found in MARSAME)
Thomas Jefferson National Accelerator Facility
Hierarchy of Control
• Hierarchy applies to all M&E
• Suspension applies to encumbered areas
Net Activity
Radioactive Material/Waste
10CFR835
O 435.1
-May not be released
-Transfer to DOE facility or other
regulated entity permitted
ANSI N13.12?
Material with Residual Activity
10CFR835
O 5400.5, G 441.1-XX
No activity detected;
Indistinguishable from background
Not regulated, “not radioactive”
-Release only under authorized limit
-Use may be restricted
-Certification under AL required
-Some controls under §835 may apply
-Fed/State/local requirements
- Unrestricted release
Adapted from LLNL-TR-409583
Thomas Jefferson National Accelerator Facility
Release of Solids (including metal)
• Majority of non-effluent releases are metal-containing solids
• JLab practice uses process knowledge and survey
• For surveys:
– Volumetric activity must be IFB for release
– When applicable, contamination survey < O 5400.5/G 441.1-XX
• Protocol changed to IFB in early 2009
– Release criteria did not change drastically, but constraints on survey
technique affected practical aspects of survey
• Nuclide & sensitivity parameters
–
–
–
–
Gamma emitters dominate in most materials
Proxies present when there is potential for hard-to-detect nuclides
Maximum concentrations near surface
Survey method is sensitive – MDC usually better than ANSI SLs
Thomas Jefferson National Accelerator Facility
Volumetric Activity Characteristics
• Activation occurs as function of the high energy particle fluence
• Activity beyond 1m insignificant fraction of surface
• Nuclides well known, mixtures contain most restrictive nuclides in
quantities that prevent HDT nuclides from being limiting
• For large objects, detector-surface distance is not a critical factor
Example Activity Profile in Metal
(Adapted from SLAC data)
1.000
Relative Concentration
Specific Activity
0.100
0.010
0.001
0
25
50
75
100
125
150
Depth in material (cm)
From SLAC RP Note RP-09-04
Thomas Jefferson National Accelerator Facility
Survey Sensitivity
JLab survey method evaluated
– JLab has been using Bicron/Thermo Micro-rem for > 15 years
– Features have been improved (audible, low-energy performance)
– Uniquely capable micro-rem meter
• Detects photons down to 17 keV (and below)
• Sensitive to beta
Thomas Jefferson National Accelerator Facility
Survey Sensitivity
JLab survey method evaluated
– MARSAME ‘Scenario B’ null hypothesis test
– Statistics based on Signal Detection Theory (NUREGs, MARSSIM)
• Accounts for “scanning” survey and human performance factors
– Analogous to Lc – level at which “signal is present”
– Minimum detectable signal was determined
– Calculated sensitivity not drastically different than JLab’s historically used
“twice background”
Normal
range of Bkg
Survey sensitivity for a non-ideal observer (5 second observation interval)
Release criterion set to “any detectable” response, with an upper bound of 5
µrem/hr (practical due to scale range and typical background)
Thomas Jefferson National Accelerator Facility
Survey Sensitivity
• For activity in volume, MDC is complex function of nuclide, material,
activity distribution, object geometry
• Reasonably large object approximates a semi-infinite slab
• MDC approaches a nuclide-specific minimum
• In real objects, near-surface concentration enhances MDC
Behavior of MDA with object size
Uniform Distribution in Iron
1000
Co-60
Mn-54
Plot Shows:
• Calculated MDC* based on 5 µrem/hr
sensitivity
• Uniform activity distribution assumed
pCi/g
100
30
10
3
1
1
10
100
1E3
1E4
1E5
1E6
Mass of object - grams
*This value is not traditional MDA, but
the activity associated with
“discernable signal”
Thomas Jefferson National Accelerator Facility
Survey Sensitivity
JLab survey method evaluated
–
–
–
–
–
–
Conducted field test of detection sensitivity
Typical items from the field were analyzed with ISOCS®
RCTs conducted surveys on items
Sensitivity good compared to N13.12 SLs
Technicians are able to identify net signal at levels below statistical expectation
Verified already-understood limitation when surveying very small items
Behavior of MDA with object size
Calculated vs. Field Evaluation
1000
Calculated MDC
Co60/Mn54 50/50
Field Test MDC
Total activity
pCi/g
100
ANSI N13.12
30
10
3
1
1
10
100
1E3
1E4
1E5
1E6
1E7
Concrete
Block
Mass of object - grams
Thomas Jefferson National Accelerator Facility
Concrete Assessment
Block 1 (Barite/Magnetite) Core B
- High-density concrete block
- 600 MeV proton synchrotron
- ~ 30 years of decay time
Activity in pCi/g
100
10
Ti44
Co60
Eu152
1
0.1
Block reads ~ 15 µR/hr
Does not meet release criterion
H3
5
10
15
20
25
30
35
Proxies protective for tritium,
but JLab protocol requires 3H
smears for material w/potential
40
Depth Interval - cm
(basis in G441.1-XX)
High density block assessment – concentrations averaged over first 20 cm depth
Nuclide
Concentration In Block (pCi/g)
ANSI Screening Limit (pCi/g)
Fraction of limit
H-3
80
3000
0.027
Co-60
Na-22
6
0.08
30
30
0.2
0.003
Eu-152
1.0
30
0.033
Eu-154
0.2
30
0.007
Ti-44
1.0
30**
0.033
** Not in ANSI, derived from NCRP 123
Sum of fractions 0.3
Thomas Jefferson National Accelerator Facility
Clearance Protocol Conclusions
-Detection sensitivity by survey correlates well to ANSI Screening
Level – in many cases small fraction of SL (<0.1 ∑ SLAii)
- Clearance of solid materials by field survey using IFB is
protective of public < 1 mrem/y
- Finely divided material, rubble, liquid (and a few exceptions)
should be volumetrically assayed with MDA < ANSI SL
Impacted Material
Potentially activated
material
Description
Type of Monitoring
Release Criteria
Solids
Direct γ Survey, H-3 smears*
IFB
Finely divided solids
Volumetric γ-spec
IFB
Liquids
Volumetric γ-spec, volumetric H-3
IFB
All surfaces
Direct scan, smears
O 5400.5
Potentially contaminated
material
* For solids having potential H-3 activity
Thomas Jefferson National Accelerator Facility
Summary of JLab Clearance Policy
• It is the policy of Jefferson Lab not to release any material from
control that is known or suspected to contain radioactive
material above background levels.
• Releases using surveys and/or analyses are based on the
criterion of “indistinguishable from background” (IFB). Such
measurements performed at JLab, have a detection sensitivity
adequate to:
- Ensure that potential dose to any member of the public from
release of the applicable material is < 1 mrem in a year, and as low
as reasonably achievable (ALARA);
- Ensure that the material would not be subject to regulatory
control by NRC, the Commonwealth of Virginia, or any other
regulatory authority;
- Meet requirements for any applicable DOE authorized limits.
Thomas Jefferson National Accelerator Facility
Summary of JLab Clearance Policy
• When material cannot be determined with reasonable
assurance to be free of added radioactivity (i.e.
radioactivity above background is detected or > Bkg
activity known by PK), the following pathways for
disposition are available:
- Decontaminate, or hold for decay, then re-survey and
release as IFB
- Conditional release for re-use on site (within constraints that
meet 10CFR835 and O 5400.5 requirements)
- Control as radioactive material
- Manage as radioactive waste
- Release under DOE approved criteria (i.e. O 5400.5 or other
authorized limit)