FLUKA Simulation of Top-off Injection Accident at National ... · FLUKA Simulation of Top-off...
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FLUKA Simulation of Top-off Injection Accidentat National Synchrotron Light Source
P.K. Job, Radiation PhysicistNational Synchrotron Light Source
FLUKA Advanced Course and WorkshopEriceira, Portugal, October 4-8, 2010
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Overview of Presentation
• National Synchrotron Light Source-II
• Top-off Injection at the Light Sources
• Top-off Injection Accident Scenarios
• FLUKA Simulation Methodology
• Geometry for FLUKA Simulation
• Results of Simulation
• Summary Results and Conclusions
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NSLS-II Electron Accelerators
Storage Ring Circumference 792 m
Linac Beam Energy 200 Mev
Linac Beam Current 15 nA
Maximum Booster Energy 3000 MeV
Maximum Booster Charge 15 nC
Top-off Injection Frequency ~1 p/min
Stored Beam Energy 3000 MeV
Stored Beam Current 500 mA
Estimated Beam Life Time ~3hrs
Beam Current Stability Specified ~1%
Booster Circumference 152 m
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Injection Region of NSLS-II
Booster Synchrotron
Linac
Maximum Booster Injection Capability : 1 Hz (15 nC/s)
Xrays are generated by the 30 Insertion Devices and 30 Dipole Magnets and come out of the Storage Ring through beam ports on the ratchet wall
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What is Top-off Injection ?
• Top-off injection is quasi-continuous injection into the storage ring atshorter intervals with the x-ray shutters open, adopted by almost allmodern synchrotron light sources. Top-off Injection makes storedbeam current to be quasi-constant (~1% for NSLS-II).
Top-off injection with shutters open
0
22
Beam current nearly constant for Top-off operation
Cu
rre
nt
[mA
]
0 2 4 6 8 10 12 14 16 18 20
Time [Hours]
Traditional injection with shutters closed
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Advantages of Top-off Injection
• Beam current stability within specified limit
• Avoid beamline shutter cycling during each injection
• Thermal stability of beamline optics avoiding drifts
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Disadvantages of Top-off Injection
X-Rays
Stored Beam
SAFE
X-Rays
Stored Beam
Electron Beam
Top-off ACCIDENT
Expt. Floor
Storage Ring
Shutter openInsertion Device Dipole
Electron Beam
Storage Ring
Expt. Floor
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Top-off Injection Accident Scenarios
• Injected electron beam conveyed down through the beamline front end and intercepted by the front end apertures, even if the magnet lattice settings are within the interlocked range with the x-ray shutters open
• Injected electron beam conveyed down through the front end to the Optics Enclosure and intercepted by the beamline components in the Optics Enclosure due to redundant interlock failures during top-off injection
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Front End Components at NSLS-II
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Radiological Simulations
• FLUKA Monte Carlo simulations have been performed to analyze the radiological implications of top-off injection accident at NSLS-II
• The full injected electron beam of 15 nC/s was made to incident on the fixed mask aperture, photon shutter or a beamline component in the First Optics Enclosure
• Ambient dose equivalent rates have been calculated along the storage ring concrete wall at the experimental floor or at around the First Optics Enclosure (occupied regions)
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Front End & Beamline Components Simulated in FLUKA
• Glidcop Fixed Mask Aperture
• Lead Collimator 1
• Glidcop Photon Shutter
• Lead Collimator 2
• Lead safety Shutters
• Storage Ring Lateral wall (Concrete)
• Storage Ring Ratchet Wall (Concrete)
• Lead Ratchet Wall Collimator (Embedded)
• Optics Enclosure Lateral Wall (lead)
• Optics Enclosure Downstream Wall (lead)
• Optics Enclosure Downstream Wall – lead -1 m2
• Optics Enclosure Copper Mask
• Bremsstrahlung Stop in the Optics Enclosure (lead)
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Front End & Beamline Components in the FLUKA Simulation
Storage RingOptics Enclosure
Expt. Floor
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Total Dose Rate DistributionInjected Beam on Front End Mask
Beam
Mas
k
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Neutron Dose Rate DistributionInjected Beam on Front End mask
Beam
Mas
k
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Total Dose Rate Distribution Injected Beam on Photon Shutter
PS1
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Total Dose Rate on Ratchet Wall inside Optics EnclosureInjected Beam on Photon Shutter
Shutters Closed Enclosure Open
Shutters Open Enclosure Closed
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Injected Beam in the Optics Enclosure
FOE
Optics Enclosure
Mask
Storage Ring
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Total Dose Rate along the Side Panel of the Optics Enclosure
FOE
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Neutron Dose Rate along the Side Panel of the Optics Enclosure
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Dose Rate along the Downstream Panel of the Optics Enclosure
Total Dose Rate
Neutron Dose rate
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Summary Results & Conclusions
• FLUKA can be effectively used to analyze the radiological consequences of top-off injection accident at Light Sources
• In the event of a full injected beam loss at the NSLS-II front end, the total dose rate at the experimental floor is < 500 mrem/h (5 mSv/h), this corresponds to 0.14 mrem (1.4µSv) per top-off injection pulse of 15 nC (Injection rate 15 nC/s)
• If injected electron beam is intercepted by the front end components inside the storage ring, the area radiation monitors on the expt. floor will be set to trip injection within a few pulses
• The neutron dose rates are calculated as 30-50% of the total dose rates (with ICRP74 weighting factors)
• In the event of full injected beam conveyed down to the Optics Enclosure, the dose rate at the experimental floor is >300 rem/h (3 Sv/h) which corresponds to ~ 80 mrem(0.8 mSv) per pulse of 15 nC
• Fast and redundant interlock systems are required to prevent even the first errant pulse entering the storage ring.
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Thanks
• FLUKA Preliminary Workshop at Houston (all the teachers)
• Alberto Fasso (my friend, philosopher and guide)
• Vasilis Vlachoudis (for flair and for answering promptly many of my silly questions)