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Radiation Safety Design of LCLS Electron Dump Using MARS15 Code System

Learn about the application of the MARS15 code system to design the radiation safety of LCLS Electron Dump. This study presents a multi-step approach to address various issues related to radiation safety at the Stanford Linear Accelerator Center. Get insights into the parameters, design criteria, difficulties faced, and methodology used to ensure safety. Explore subsection calculation, shielding design, and get results on dose rate distribution.

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Radiation Safety Design of LCLS Electron Dump Using MARS15 Code System

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  1. Application of MARS15 code system to radiation safety design of LCLS electron dump-Multi-step approach and LCLS- T.Sanami Stanford Linear Accelerator Center / High energy accelerator Organization (KEK) N.Nakao Fermi National Accelerator Laboratory X.S.Mao and S.Rokni Stanford Linear Accelerator Center May 24, 2007 MARS15 course @ FNAL

  2. Linac Coherent Light Source =LCLS LCLS schematic view Front End Enclosure (FEE) Near Experimental Hall (NEH) X-ray tunnel Far Experimental Hall (FEH)

  3. New construction part Beam Transport Hall West (BTW) (existing and not shown) - 110 m from 60 ft muon steel plug east to Research Yard Wall Undulator Hall (UH) – 170 m long underground tunnel housing undulators Beam Transport Hall (BTH) – 227 m long above grade facility to transport the electron beam through the existing RSY Near Experimental Hall (NEH) – underground facility whose primary function is to house 3 experimental hutches, and prep areas. Wall 1 336,000 lbs steel Wall 2 252,000 lbs steel Far Experimental Hall (FEH) – underground single 46’ cavern to house 3 experimental hutches and prep space Electrons Electron Beam Dump (BD) – 40 m long underground facility used to separate the electron and x-ray beams X-Rays Front End Enclosure (FEE) – 35 m long underground facility to house various diagnostic equipment in support of the photon beam 786 m (1/2 mile) X-Ray Transport & Diagnostics Tunnel (XRT)– 200 m long underground tunnel used to transport photon beams from NEH to FEH

  4. Parameters for LCLS • Beam parameter • Injector: 135 MeV, 16 W • LINAC: 13.6 GeV, 5 kW • Max. Cred. Beam: 16 GeV, 100 kW • X-ray: 140 keV, 2.8 W • FEL: 8.2 keV, 0.3 W • Design Criteria • 0.5 mrem/h for control access area, normal operation • 0.05 mrem/h for experimental area and outside, normal operation • 400 mrem/h for mis-steering situation • 25 rem/h for maximum credible beam loss

  5. Issues should be addressed • Prompt dose of FEE • Prompt dose of the ground surface • Ground water activity • Residual dose rate • Prompt dose of NEH Tune-up dump: 420W Collimaters: 20 W Thin insertion devices (WS,OTR): 5 kW Dump: 5kW Brems: 800mW BYD: 20W 2 FEE NEH 5 4 1 3 MARS15 and Fluka

  6. Difficulties • Complex geometry and thick shield • Attenuation of up to 6 m thick concrete and soil • 0 degree dose rate estimation → Subsection calculation • Several beam losses and operation modes • Check the contribution form each beam loss • Sum-up the contribution for each mode → Use same XYZHIS.INP which allows sum up later • Estimate 3T activity close to the detection limit in ground water • Residual dose rate

  7. Methodology • Geometry description • Produce GEOM.INP from fortran code Easy to describe relationship between devices and materials • Change material for specified region • Activities and average dose rate • Zmin and Zmax • Take out unnecessary area • Subsection calculation • Reduce computation time • Usage of Multi-CPU

  8. Subsection calculation • Dived one geometry to several subsection • Accumulate leak events as source events for the next subsection • Why do we need? r=10m → S=4p×106 cm2 r 106 source particle →1/4p #/cm2 Surface: S Without attenuation ! Source For the beam dump case: 5 kW beam loss = 1011 mrem/h → 10-2 mrem/h using distance and shield = Difference: 13 order of magnitude

  9. How to perform subsection calculation • Example of how to code user routine • T.Nunomiya, N.Nakao, H.Iwase, T.Nakamura, “Deep-penetration calculation for the ISIS target station shielding using the MARS Monte Carlo code”, KEK Report 2002-12 • Prepare at least tow kind of executable, one for initial and the other for continuous calculation, by modifying user routine, m1505.f • First subsection Define subsection using reg1.f Dump leak event using leak.f • Second, third,,,, Read leak event using beg1.f Define subsection using reg1.f Dump leak event using leak.f

  10. Shielding design around the dump - Bulk Cover Soil 197” soil Concrete wall Muon shield 1 36” 48” 36” 150” air Wall 1 Dump pit 55” Iron 36” 70” Dump pit wall 36” 67” concrete Dump pit iron Dump • Density • Concrete : 2.35 gcc : Soil : 2.1 gcc • Iron : 7.87 gcc : Copper : 8.96 gcc • SUS : 7.92 gcc : Air : 1.21E-3 gcc 36” 67”

  11. Subsections for main dump calculation • Example of Subsections 1 2 3 4 5 6 7 Computing time , the number of leak event, valance of attenuation, particle type, energy distribution

  12. Results – dose rate distribution on elevation view 13.64 GeV, 5 kW < 0.1 mrem/h 0.0001 mrem/h 0.001 mrem/h 0.01 mrem/h 16.44ft soil 0.1 mrem/h 1 mrem/h 10 mrem/h 3ft 100 mrem/h air < 0.5 mrem/h Iron 4ft 3ft 1 rem/h 12.5ft 3ft 70 inch concrete 67 inch < 0.5 mrem/h [mrem/h] [mSv/h]

  13. Results – comparison with SHIELD11 result on elevation cut 13.64 GeV, 5 kW Dump line Beam line Ground surface Surface of concrete Tunnel Conc+Soil 0.5rem/h 0.05mrem/h

  14. Comparison to one-through calculation 6.4×108 total history Subsection 4.5×108 history One through 4.6×108 history One through Muon transportation off Muon transportation on BIAS 2=0.2 0.2 0.2 Muon transportation on BIAS 2=0.0 0.0 0.0 0.2

  15. 3. Estimation of groundwater activity • Procedure • Production rates of 3H for nominal operation, i.e. 2 kW, 300 days/year operation • Water activity with assumptions of • for 1 m x 1 m x 1 m cubic soil volume • Water content : 30 wt% of soil • Isotope transfer : 100 % (= 3H made in soil goes to water) • 1 m/year water flow in soil, which result in 4 years irradiation Results Water activity in 1 m3 soil block : 300 pCi/L → 3.3 times lower than EPA detection limit Groundwater table is 35’ away from this region → No effect to groundwater.

  16. 4. Result – residual dose of the dump Elevation view Plain view concrete concrete iron iron 1 day cooling time → 10 rem/h on contact (Dump) [mrem/h] [mSv/h]

  17. Conclusion • MARS15 code is employed for radiation safety design of LCLS 13.64 GeV, 5kW, electron dump • Subsection technique • Prompt dose • Ground water activity • Residual dose

  18. Overall geometry from beam dump line to NEH Z=68725 Z=72194 Z=75649 100m Beam dump hall FEE NEH Plain view ST1 ST2 PMs ST3 Safety dump PCPM1 Main dump Elevation view By MARS15 Geometry plotter

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