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T.Sanami Stanford Linear Accelerator Center / High energy accelerator Organization (KEK) N.Nakao

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

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T.Sanami Stanford Linear Accelerator Center / High energy accelerator Organization (KEK) N.Nakao

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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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