Clearance Protocol for Lead at Accelerator Facilities 1 Clearance Protocol for Lead at Accelerator Facilities James Liu, Maranda Cimeno, Ted Liang, Ludovic Nicolas and Henry Tran Radiation Protection Department SLAC National Accelerator Laboratory, CA, USA ARIA2017, Lund, Sweden, May 22-24, 2017

Outline Progress of clearance of common metals at SLAC 2 Outline Progress of clearance of common metals at SLAC Development of lead clearance protocol: Induced activity characteristics from FLUKA calculations: Dominated by Tl-204 (a hard-to-measure, pure-beta-emitting radionuclide) Development of clearance measurement method: Clearance criteria: measurements are indistinguishable from background (IFB) Have to Use a large-area GM survey meter Detection threshold (DT) is lower than ANSI N13.12-2013 Screening Level (1 Bq/g for Tl-204) Conclusions

US Regulations and Standards for Clearance 3 US Regulations and Standards for Clearance DOE Order 458.1 “Radiation Protection of the Public and the Environment”, 2011 (chg 3, 2013): dose criterion of 10 Sv/y ANSI N13.12 “Surface and Volume Radioactivity Standards for Clearance” (2013): Dose-risk-dependent Screening Level (SL in Bq/g) Radionuclide Group in ANSI N13.12 SL (Bq/g) Group 1: High-energy gamma, radium, thorium, transuranics, and mobile beta-gamma emitters (e.g., 22Na, 46Sc, 54Mn, 56Co, 60Co, 65Zn, 152Eu, 182Ta, 207Bi) 0.1 Group 2: Uranium and selected beta-gamma emitters (e.g., 57Co, 58Co, 59Fe, 113Sn, 185Os, 204Tl, 206Bi) 1 Group 3: General beta-gamma emitters (e.g., 7Be, 202Tl) 10 Group 4: Low-energy beta-gamma Emitters (e.g., 3H, 45Ca, 63Ni) 100 Group 5: Low-energy beta emitters (e.g., 55Fe) 1000

SLAC Clearance Protocol for Common Metals SLAC RPD-010 “SLAC Material Release Program Manual” 2011 Metal Induced Radionuclides Half-life Aluminum 22Na (proxy) 2.6 y Carbon Steel (Fe, C) Cast Iron (Fe, C, Si, Mn) 54Mn (proxy) 312 d 55Fe (5.9 keV X-ray) 2.73 y 57Co 272 d Copper 60Co (proxy) 5.26 y Radionuclides with long half-lives are of interest Hard-to-measure radionuclides (55Fe), which emit only low-energy X rays or beta rays Proxy radionuclides (22Na, 54Mn, 60Co), which emit high-energy and high-intensity gamma rays ANSI N13.12 SL: 55Fe: 1000 Bq/g 22Na, 54Mn, 60Co: 0.1 Bq/g From FLUKA calculations, SLAC technical bases show that: Evaluation: ∑i (Ai / SLi)  1 Measurements with IFB criterion: ∑i (DTi / SLi)  1

SLAC, JLAB, ORNL, SNL, ORNL, and US DOE 5 DOE-STD-6004 (2016): 7 Chapters SLAC, JLAB, ORNL, SNL, ORNL, and US DOE Purpose and Scope Introduction Material Clearance Protocols Documentation and Reporting Requirements DOE Independent Verification, Stakeholder Communication References Common Acronyms and Definitions

DOE-STD-6004 (2016): 5 Appendices Rationale for Endorsement of ANSI N13.12-2013 SLs as DOE Pre-Approved Authorized Limits Process Knowledge for Volumetric Activation in Accelerator Facilities Technical Basis for Volumetric Activation at Electron Accelerator Facilities Technical Basis for Volumetric Activation at Proton Accelerator Facilities Technical Basis for Measurement Methods of Volumetric Radioactivity and Determination of Detection Capabilities Appendices C and D: “proxy” radionuclides in materials are identified for effective measurements in the field  

SLAC Instruments for Common Metal Clearance Measurements Ludlum Model 2241 meter with 1”x1” NaI probe (DT ~ 0.03 Bg/g; 30 nSv/h) & small-area GM pancake probe Field Gamma Spectrometer Portal Gate Monitor

Excess Metal at SLAC (before clearance) 8 Excess Metal at SLAC (before clearance)

Excess Metal at SLAC (after clearance) 9 Excess Metal at SLAC (after clearance) 3528 tons , $1,479,318 loads First DOE Lab to release metals 6-2011 to 4-2017: 157 tons Al, 271 tons Cu, 3441 tons steel, 493 truck loads, $2.05M

How About Clearance for Lead? 10 How About Clearance for Lead? Common shielding material: may become expensive, mixed waste (radioactive and hazardous) 82 tons (10 m3) of lead stored at SLAC FLUKA shows that Tl-204 (pure beta emitter) dominates and no proxy radionuclides FLUKA calculation gives sensitivity of small-area GM probe (8 cpm per Bq/g of Tl-204 in lead) Developed IFB clearance measurement method using a large-area GM probe with a detection threshold (DT) that is quantified to be < ANSI SL of 1 Bq/g

Key Radionuclides from Activated Lead for Clearance 11 Key Radionuclides from Activated Lead for Clearance Radionuclide Half-life Emission Yield Energy (keV) ANSI N13.12 Group SL (Bq/g) Os-185 96.6 d gamma 78% 646 2 1 Pt-193 50 y beta 100% 56.6 3 10 Tl-202 12.2 d 91% 440 Tl-204 3.78 y 97% 763 Bi-205 15.3 d 31% 703 Bi-206 6.24 d 99% 803 Bi-207 31.6 y 98% 570 0.1 g,n and g,p and g,np and g,spallation Reactions leading to induced radionuclides (p,n) (,n) (,p) (,np) (,np)

Gamma Spectrum for Activated Lead 12 Gamma Spectrum for Activated Lead An experiment: 3 days irradiation and 21 days decay at SLAC FACET 0.3 µSv/h on contact (gammas from Tl-202, Bi-205, Bi-206) Agreed with FLUKA, which also shows that Tl-204 (pure beta emitter) would dominate after 90 days Tl-201 Hg-197 Tl-202 g,n and g,p and g,np and g,spallation Bi-205 Bi-206 Tl-204

FLUKA Calculations of Lead Activation 13 FLUKA Calculations of Lead Activation Radionuclides and activities normalized to 1 W for irradiation of 1 and 10 years at decay from 1 day to 1 year PRESICIO, PHOTONUC, RADDECAY, DCYSCORE, RESNUCLE IRRPROF, DCYTIMES

Activity versus Lead Layer 14 Activity versus Lead Layer 1 year irradiation 1 day decay Number after isotope ID is slope (attenuation length of reaction in lead in g/cm2) Tl-202 53 Bi-205 18 Pt-193 44 Tl-204 51 Os-185 Bi-206 17 Bi-207 22

Radionuclides in Inner 1-cm-thick Lead Layer 15 Radionuclides in Inner 1-cm-thick Lead Layer Dose Risk (Activity / SL) for 1 & 10 year irradiation Tl-204 Tl-202 Bi-207 Tl-204 Bi-206 Bi-206 Bi-205 Bi-205 Tl-202 Bi-207 Os-185 Os-185 Pt-193 Table for the 7 isotope’s decays, emission, and SLs Tl-204 (pure beta emitter) has highest activity and dose risk in most cases No easy-to-detect “proxy” gamma emitter after a few months decay

Tl-204 Beta Spectrum from FLUKA 16 Tl-204 Beta Spectrum from FLUKA Tl-204 beta spectrum (Emax of 0.764 MeV) FLUKA-generated beta spectrum agrees with ICRP38 Simulation of GM probe sensitivity FLUKA built-in isotope source BEAM, ISOTOPE, HI-PROPE (Tl-204, Z=81, A=204) Beta decay RADDECAY Score transport of beta decays DCYSCORE

FLUKA Calculations of GM Probe Sensitivity for Tl-204 in Lead 17 FLUKA Calculations of GM Probe Sensitivity for Tl-204 in Lead Tl-204 inside lead sheet Tl-204 betas emitted isotopically inside lead Lead thickness 0.05 cm (range of Tl-204 betas) and radius 5 or 8 cm GM probe (2.5 cm radius) Steel wire thickness 0.03 cm Wire spacing 0.125 cm 0.5 or 1 cm to lead 15.5 cm2 GM probe FLUKA scoring “USRBDX”: one-way current passing from lead region to GM gas Lead to Air Air to GM Mica Window Window to Ne-Cl Gas Steel wire mesh (32x32 wires covering 35% of window area; wire diameter = 475 keV beta range) is critical.

Sensitivity of GM Probe (active area 15.5 cm2) 18 Sensitivity of GM Probe (active area 15.5 cm2) GM at 1 cm from thin Pb (5 cm radius) Region I Region II e-/min per Bq/g of Tl-204 Ratio to Source Source 2661 100% Lead Air 145 5.4% Window 8.1 0.31% Gas 7.5 0.29% FLUKA Geometry of Lead and GM Probe GM Sensitivity (e-/min per Bq/g of Tl-204) GM at 0.5 cm from Pb brick (5 cm radius) 8.0 GM at 1 cm from Pb brick (5 cm radius) 7.5 GM at 2.5 cm from Pb brick (5 cm radius) 6.7 GM at 1 cm from Pb brick (8 cm radius) 7.7

GM sensitivity calculated 19 Benchmark of FLUKA Calculations of Small-Area GM Sensitivity with Three Tc-99 Beta Sources 5 µm Tc-99 source GM window FLUKA-generated Tc-99 beta spectrum (Emax 0.294 MeV) Tc-99 AH-1333 5 cm diameter TC-99 Source AH-1334 AH-1333 AH-1336 GM sensitivity calculated by FLUKA (e-/min/Bq) Activity (Bq) 313 381 417 Base/Probe SN Measured GM Sensitivity (cpm/Bq) 261372/197115 9.7 (7%) 9.9 (7%) 8.9 261297/197100 9.9 (8%) 10.1 (7%)

Need to Use Large-Area GM Meters for Lead Clearance Measurements 20 Need to Use Large-Area GM Meters for Lead Clearance Measurements   Ludlum Model 44-94 four LND 7311 GM probes 4 x 15.5 = 62 cm² active area x4 sensitivity, x4 background x½ detection threshold (DT) Lead Clearance On-contact Measurements Ludlum 44-9 GM Probe 15.5 cm2 active area

Detection Thresholds of GM Meters 21 Detection Thresholds of GM Meters GM on contact with Lead Brick Detection Threshold DT (Bq/g of Tl-204) 44-9 (15.5 cm2) 40 8 1.8 44-94 (4x15.5 cm2) 120 32 0.8 ANSI N13.12 SL of 1 Bq/g Static, 1-min measurement both sides of lead brick  

22 Conclusions DOE Standard DOE-STD-6004 (2016) was developed for clearance of common metals (e.g., Al, Fe and Cu) in accelerator facilities Unlike common metals, there are no proxy radionuclides for lead clearance measurements in electron accelerators Tl-204 (pure beta emitter, Emax = 764 keV, 3.78 yr) dominates activity and risk in lead in most cases Sensitivity of a small-area (15.5 cm2) GM probe for Tl-204 in lead was calculated with FLUKA to be 8 cpm per Bq/g. With an average background of 120 cpm, detection threshold of a large-area GM meter (4x15.5 cm2) can be 0.8 Bq/g for Tl-204 inside lead, which is lower than ANSI N13.12 SL of 1 Bq/g. Lead clearance measurement protocol (e.g., static 1-min measurements with large-area GM probe on contact with a lead brick under maximum background of 180 cpm) is being developed to meet IFB release criterion.