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Material Release Protocols Used at Thomas Jefferson National Accelerator Facility PowerPoint Presentation
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Material Release Protocols Used at Thomas Jefferson National Accelerator Facility

Material Release Protocols Used at Thomas Jefferson National Accelerator Facility

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Material Release Protocols Used at Thomas Jefferson National Accelerator Facility

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  1. 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

  2. Jefferson Lab Facilities CEBAF Accelerator Free Electron Laser 6 GeV, 1MW CW Electron Beam Recirculating LINAC 120 MeV, 1.2 MW CW Electron Beam 120 kW Energy Recovery LINAC

  3. 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

  4. 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

  5. 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

  6. 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

  7. Hierarchy of Control • Hierarchy applies to all M&E • Suspension applies to encumbered areas Radioactive Material/Waste 10CFR835 O 435.1 • May not be released • Transfer to DOE facility or other regulated entity permitted Net Activity ANSI N13.12? • Release only under authorized limit • Use may be restricted • Certification under AL required • Some controls under §835 may apply • Fed/State/local requirements Material with Residual Activity 10CFR835 O 5400.5, G 441.1-XX No activity detected; Indistinguishable from background Not regulated, “not radioactive” • - Unrestricted release Adapted from LLNL-TR-409583 Thomas Jefferson National Accelerator Facility

  8. 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

  9. 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 From SLAC RP Note RP-09-04 Thomas Jefferson National Accelerator Facility

  10. 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

  11. 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

  12. 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 • Plot Shows: • Calculated MDC* based on 5 µrem/hr sensitivity • Uniform activity distribution assumed • *This value is not traditional MDA, but the activity associated with “discernable signal” Thomas Jefferson National Accelerator Facility

  13. 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 Thomas Jefferson National Accelerator Facility

  14. Concrete Assessment • - High-density concrete block • 600 MeV proton synchrotron • ~ 30 years of decay time 100 10 1 0.1 Block reads ~ 15 µR/hr Does not meet release criterion Proxies protective for tritium, but JLab protocol requires 3H smears for material w/potential (basis in G441.1-XX) High density block assessment – concentrations averaged over first 20 cm depth Thomas Jefferson National Accelerator Facility

  15. Clearance Protocol Conclusions • Detection sensitivity by survey correlates well to ANSI Screening Level – in many cases small fraction of SL (<0.1 ∑ ) • 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 Ai SLi * For solids having potential H-3 activity Thomas Jefferson National Accelerator Facility

  16. 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

  17. 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)