2. 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 1

3. 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

4. 3 Notes SLAC measurement protocol for volumetric radioactivity: –Release criterion of IFB (specific activities for natural radioisotopes, e.g., thorium and 40 K, 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.

5. 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)

6. 5 Radioisotopes of Interest in Metals and Concrete MaterialRadionuclideHalf-life Carbon steel (Fe, C) & Cast iron (Fe, C, Si, Mn) 22 Na (proxy)2.6 y 54 Mn (proxy)312 d 55 Fe (5.9 keV x-ray)2.73 y 57 Co272 d Aluminum 22 Na (proxy)2.6 y Copper 55 Fe (5.9 keV x-ray)2.73 y 57 Co272 d 60 Co (proxy)5.26 y Concrete 3 H (pure beta)12.3 y 22 Na (proxy)2.6 y 54 Mn (proxy)312 d 55 Fe (5.9 keV x-ray)2.73 y 57 Co272 d 60 Co5.26 y 152 Eu, 154 Eu13.5 y, 8.59 y Proxy radioisotopes ( 22 Na, 54 Mn, 60 Co), which emit high- energy and high-intensity gamma rays 10  Sv/y  ANSI N13.12 Screening Level (SL): 22 Na, 54 Mn, 60 Co: 30 pCi/g 55 Fe, 3 H: 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 ( 55 Fe, 3 H), which emit only low- energy X rays or beta rays.

7. 6 Hard-to-Measure and Proxy Radioisotopes for BaBar RadioisotopeHalf-life FLUKA-Calculated Specific Activity in pCi/g (% of total) 1 year2 years5 years 60 Co (proxy)5.3 y1.0×10 -6 (22%)8.9×10 -7 (27%)6.0×10 -7 (38%) 57 Co272 d9.4×10 -8 (2%)3.7×10 -8 (1.1%)2.3×10 -9 (0.1%) 55 Fe2.7 y2.4×10 -6 (53%)1.9×10 -6 (57%)8.8×10 -7 (55%) 54 Mn (proxy)313 d6.5×10 -7 (14%)2.9×10 -7 (9%)2.5×10 -8 (1.6%) 49 V338 d2.7×10 -7 (6%)1.3×10 -7 (4%)1.4×10 -8 (0.9%) 3H3H12.3 y6.9×10 -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 55 Fe is much less than (SA/SL) for 60 Co

8. 7 Examples of Measured Nuclides in Metals Item No. Component (Material) 1 Radioisotope Dose Rate (mR/h) Activity 2 (pCi/g) Activity Ratio to Co-60 3 ANSI N13.12 SL (pCi/g) 090826-002Al piece (Al) Co-600.0342130 Na-220.03451.430 090826-006Iron Sheet (Fe) Co-600.02301 Na-220.02320.0430 070703-00134-ft beam pipe (SS)Co-600.0464130 090921-002Dump (Cu, SS)Co-600.176130 090904-001Iron plates/blocks (Fe) Co-600.4293130 Mn-540.41092230 080918-001Ballast (Fe, Cu) Co-600.0246130 Mn-540.021491.330 Na-220.02500.330 Zn-650.022220.230 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.

9. 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 55 Fe follow the bremsstrahlung photon attenuation profile (1/1000 reduction per meter), –Spallation products such as 3 H and 22 Na follow the high-energy neutron attenuation profile (1/10 reduction per meter), –Thermal-neutron-capture products such as 60 Co and 152 Eu also follow the high-energy neutron attenuation profile (1/10 reduction per meter), but their magnitudes depend on Co and Eu trace elements

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

11. 10 FLUKA-calculated Activity Profiles in Concrete Wall Depth (cm) 55 Fe / 22 Na  10 3 H / 22 Na  5 10-year irradiation and 5-year decay Activity (Bq/g/W) 55 Fe / 22 Na  2

12. 11 Examples of Measured Nuclides in Concrete Item #DescriptionRadioisotope Activity (pCi/g) ANSI SL (pCi/g) SL FractionNotes S02521 FFTB Core Sample C-3 Co-602630 2.0 Easily Detectable Fe-596300 Mn-541430 Na-221630 Sc-4643300 Total1070.2 mR/h S03232 Concrete Sample from PEP-II IR-10 Tune-up Dump Wall Zn-65130 0.6 Detectable Co-580.230 Co-60930 Eu-152330 Mn-54130 Na-22330 Total180.02 mR/h

13. 12 Hard-to-Measure and Proxy Radioisotopes in Concrete The specific radioactivity for hard-to-measure radioisotopes ( 55 Fe and 3 H) can be higher than the main proxy radioisotope ( 22 Na). Bounding condition for applicability of proxy radioisotope approach is ~20 years decay time for the activity ratio of 3 H-3/ 22 Na to exceed their ANSI Screening Level ratio of 100. One solution is to conduct surface swipe or collect sample for 3 H counting. If Co and Eu trace elements exist, the radioisotopes of 60 Co and 152 Eu can serve as better proxy radioisotopes for 3 H for concrete blocks with very long decay times (tens of years).

14. 13 SLAC 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

15. 14 SLAC Volumetric Radioactivity Measurements InstrumentField Survey TechniqueProcedures & TBD Notes Ludlum 2241 or 18 Meter with 44-2 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-018 2) FO-042 3) SLAC-I-760- 2A26J-017 and - 028 Conservative efficiency & MDA calculated for proxy radioisotopes (related to point-source calibration) MDA  3 pCi/g ( 22 Na, 54 Mn, 60 Co) MDA  25 pCi/g ( 57 Co) ANSI N13.12 Screening Levels (SL): 1. High dose beta-gamma emitters ( 22 Na, 54 Mn, 60 Co): 30 pCi/g 2.General beta-gamma emitters ( 57 Co): 300 pCi/g 1) ANSI N13.12 SL values were based on 10  Sv/y dose risk 2) ∑ i (MDAi / SLi)  1

16. R Z MDA 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 15

17. 16 SLAC Surface Contamination Measurements InstrumentProtocolProceduresNotes Fixed Contamination GM Pancake 1.For beta-gamma isotopes 2.Background < 100 cpm 3.Scan item 2”/s within ½” of surface 4.Scan entire surface area 5.If net < 100 cpm, the item is not radioactive FO-018 FO-032 FO-031 SLAC-I-760- 2A26J-024 and -027 Maximum MDA = 1000 dpm/100 cm 2 DOE 5400.5 Authorized Limit (AL): beta-gamma emitters = 5,000 dpm/100 cm 2 Loose Contamination GM Pancake 1.For beta-gamma isotopes 2.Background < 100 cpm 3.Swipe 100 cm 2 area 4.Count swipe for 20 s 5.If net < 100 cpm, the item is not radioactive FO-018 FO-032 FO-031 SLAC-I-760- 2A26J-024 and -027 Maximum MDA = 1000 dpm/100 cm 2 DOE 5400.5 Authorized Limit (AL): beta-gamma emitters = 1,000 dpm/100 cm 2 1) ∑ i (MDA i / AL i )  1

18. 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

19. 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 3 H) Surface swipe for 3 H and 55 Fe LSC analysis Portal Gate Monitoring: –Detection limits about 1  Ci for proxy isotopes –Useful to supplement the field measurements

20. 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

21. 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 40 K –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

22. 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 22 Na is 3.6E-4 mSv/h/MBq at 1 m. Therefore, 1340 pCi of a 22 Na 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 22 Na. This amounts to a mass of 1340/3 = 440 g or 60 cm 3 for iron. This is consistent with  value and the common instruments’ detection limits.

23. 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

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

25. FLUKA Calculations of Induced Activity in BaBar Detector 24 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

26. 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

27. 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. 26