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SLAC Measurement Protocols for Unrestricted Release of Metals and Concrete

1. SLAC Measurement Protocols for Unrestricted Release of Metals and Concrete. James Liu, Jim Allan, Sayed Rokni, Amanda Sabourov Radiation Protection Department SLAC National Accelerator Laboratory. DOE Accelerator Safety Workshop, August 17-19, 2010, SLAC, CA.

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SLAC Measurement Protocols for Unrestricted Release of Metals and Concrete

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  1. 1 SLAC Measurement Protocols for Unrestricted Release of Metals and Concrete James Liu, Jim Allan, Sayed Rokni, Amanda Sabourov Radiation Protection Department SLAC National Accelerator Laboratory DOE Accelerator Safety Workshop, August 17-19, 2010, SLAC, CA

  2. Summary 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

  3. 3 Notes 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.

  4. Activation 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)

  5. Radioisotopes of Interest in Metals and Concrete Radioisotopes with long half-lives are of interest. Hard-to-measure radioisotopes (55Fe, 3H), which emit only low-energy X rays or beta rays. Proxy radioisotopes (22Na, 54Mn, 60Co), which emit high-energy and high-intensity gamma rays 10 Sv/y  ANSI N13.12 Screening Level (SL): 22Na, 54Mn, 60Co: 30 pCi/g 55Fe, 3H: 3000 pCi/g (100 Bq/g) Detection Limit requirement: ∑i (MDAi / SLi)  1

  6. Hard-to-Measure and Proxy Radioisotopes for BaBar Radioactivity in the BaBar IFR forward steel plug at three decay times (SA/SL) for 55Fe is much less than (SA/SL) for 60Co

  7. Examples of Measured Nuclides in Metals • All items were identified as radioactive and have been processed as radioactive waste. • Conservatively calculated assuming the dose was coming from a single radioisotope. • Determined using field gamma spectroscopy.

  8. Radioactivity 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

  9. 9 FLUKA-calculated Activity Profiles in Concrete Wall Surface Maximum Photonuclear 1/1000 in 1-m 55Fe / 22Na 10 Activity (Bq/g/W) Spallation 1/10 in 1-m 55Fe / 22Na 2 3H / 22Na 2 Depth (cm) • Cylindrical concrete tunnel • 10-year irradiation and 1-year decay • Calculated profiles agree with KEK measurements

  10. FLUKA-calculated Activity Profiles in Concrete Wall 55Fe / 22Na 10 Depth (cm) Depth (cm) Activity (Bq/g/W) 55Fe / 22Na 2 3H / 22Na 5 Depth (cm) Depth (cm) 10-year irradiation and 5-year decay

  11. Examples of Measured Nuclides in Concrete

  12. Hard-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).

  13. SLAC Field Survey Instruments Ludlum Model 18 with 44-2 detector Ludlum Model 2241 with both a 44-2 detector (1” NaI) and a GM pancake TBM P15

  14. SLAC Volumetric Radioactivity Measurements 1) ANSI N13.12 SL values were based on 10 Sv/y dose risk 2) ∑i (MDAi / SLi)  1

  15. 15 MDA Calculations Using MCNP Detector near Object Surface Z Metal with Potential Volumetric Activation R MDA = 4 B / η Sensitivity [η incpm/(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

  16. SLAC Surface Contamination Measurements 1) ∑i (MDAi / ALi)  1

  17. 17 Graded 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

  18. 18 Additional 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

  19. 19 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

  20. 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

  21. 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.

  22. Summary 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

  23. 23 Potential Activation in Electron Accelerators Tunnel Bremsstrahlung Photons Electron Beam Loss • Spallation • Photonuclear • (n,) High-Energy and Low-Energy Neutrons

  24. 24 FLUKA Calculations of Induced Activity in BaBar Detector 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 Three-Floor-High, Thousands Pieces

  25. Calculated 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

  26. 26 Measured Activity Depth Profiles in Concrete 220 MeV 45 MeV 1.3 GeV 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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