1 BROOKHAVEN SCIENCE ASSOCIATES Presentation to ASAC R. Casey Radiation Shielding: Assumption and...
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Transcript of 1 BROOKHAVEN SCIENCE ASSOCIATES Presentation to ASAC R. Casey Radiation Shielding: Assumption and...
1 BROOKHAVEN SCIENCE ASSOCIATES
Presentation to ASAC
R. Casey
Radiation Shielding: Assumption and Design
April 24, 2007
2 BROOKHAVEN SCIENCE ASSOCIATES
Preliminary Shielding Design Documents for NSLS II
1. Linac, NSLS II- TN 122. Booster & Storage Ring, NSLS II – TN 133. Storage Ring Supplemental Shielding – TN 214. Beamlines and Front Ends, NSLS II – TN 145. Ray Tracing Standards, NSLS II – TN 206. Activation Analysis, NSLS II – TN 15 & 16
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Radiation Safety Workshop was Recently Conducted
• March 27 – 28, 2007
• Membership• S. Rokni (Chair) – SLAC• R. Donahue – ALS• P. Berkvens – ESRF• D. Beavis – BNL• C. Schaefer - BNL
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Rad Safety Workshop
• Committee reviewed:• Shielding methodology & assumptions• Interlocks, Critical Devices, and Area Radiation Monitoring
plans.
• Committee concluded:
“Given the status of the project, the design of the bulk shielding of the accelerator complex is well developed and is based on sound principles and reasonable assumptions. “
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Desired Shielding Outcome
• Compliance with DOE Orders, Part 835, and BNL Administrative Controls
• < 25 mRem/year (.25 mSv) on-site to non-NSLS-II personnel; < 5 mrem/year (0.05 mSv) at site boundary
• Radiation exposure to users and staff ALARA – an administrative control level of 100 mRem/year (1 mSv) is desired
• We plan to achieve this through shielding and engineering controls; & supplemental administrative controls
• Based on current experience, we expect annual radiation exposures < < 100 mRem/year (1 mSv) to NSLS staff and users
• After verification, we expect short-term visitors will not be required to have dosimeters routinely
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Shielding Policy
• Accelerator and beam line enclosures will be shielded to reduce exposure at the exterior surface of the shield during typical operation to 0.25 mRem/hr (2.5 uSv) in normally occupied areas to limit the maximum exposure to 500 mrem/year (5 mSv) (assuming 2000 hours occupancy).
• The storage ring outer wall will be shielded to 0.5 mRem/hr (5 uSv/hr) in direct contact with exterior; no full-time occupancy is expected or will be permitted within 1 meter of wall.
• This policy satisfies DOE Design Goals identified in 10 CFR 835.1002
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Shielding Policy (cont.)
• Shielding calculations will use conservative source terms and attenuation factors
• Abnormal operating conditions, including Maximum Credible Incidents (MCI), will be evaluated
• Additional engineering or administrative controls will be specified based on severity of radiation levels under fault or non-typical conditions.
• Shielding and controls are considered adequate if MCI has low potential for exceeding 100 mRem (1 mSv) and can not exceed 2000 mRem (20 mSv)
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Shielding Policy (cont.)
Engineering control options include:• Additional shielding (e.g. shadow shields, localized shields)• Beam loss monitors with alarm in control room and (perhaps)
interlock function• Beam current monitors with alarm in control room and
(perhaps) interlock function• Area radiation monitors at the occupied areas with alarm
locally and in control room and interlock function
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Shielding Policy (cont.)
Supplemental Administrative control options include:• Operational procedures for operators and ESH staff
during injection and routine operations • Commissioning and shielding verification procedures• Shielding configuration control• Review of accelerator and beam design modifications• Survey and posting procedures• Passive area monitors
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Bulk Shielding Calculation Methodology
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Radiation Dose Equivalent Factors at 900
(comparison)
Radiation Component
Dose equivalent factors(mrem.m2/J)
(Swanson)
Dose equivalent factors(mrem.m2/J)(Sullivan)
Dose equivalent factors(mrem.m2/J)(Shield 11)
Bremsstrahlung 2.80 1.39 1.12
Giant Resonance Neutrons
0.63 0.27 0.257
High Energy Neutrons
0.075 0.043 0.068
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Radiation Attenuation FactorsUsed in Calculations
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Accelerator Operating Conditions used in Calculations
• Linac• 200 MeV• 20 nC/pulse• I hz operation
• Booster• 3.6 GeV• 15 nC per pulse• 1 pulse / minute (typical operation) • 1 hz operation for 500 hours per year considered
• Storage Ring• 3.6 GeV• 500 mA
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Beam Loss Assumptions for Normal Operations
• Linac – 1% distributed loss at 200 MeV
• Linac to Booster injection efficiency – 50%
• Booster losses – 2% loss at any point at 3.6 GeV
• Booster to storage ring injection efficiency – 80%
• Non-injection region – 10% of stored beam losses at any point
• Stops in linac and booster designed for 100% loss at 1 hz
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LINAC Bulk Shielding Estimates
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Booster Bulk Shielding Estimates1
Inboard wall(cm)
Outboard wall(cm)
Roof(cm)
Booster Injection Region2
108 108 98
BoosterNon-injection Region
95 95 80
1 The Inboard and Outboard walls are at 1 m and the roof at 2 m from the beam2 Supplemental lead shielding will be required around injection septum for 1 hz operation
Booster shielding still in progress as adjacent occupancies are under discussion.
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Storage Ring Bulk Shielding Estimates
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LINAC - Credible Radiation Incidents
• 100 % of maximum accelerated beam is lost at some location in the linac enclosure, (20 nC/s is continuously lost)
Dose Rate = 37.5 mRem/h (0.37 mSv/h) (at the exterior of shield on contact)
• 100 % injected beam to the booster is continuously lost at the linac-booster injection septum at 1 Hz.
Dose Rate = 30 mRem/h (0.3 mSv/h)
Mitigation/ control to prevent significant exposure• Area Radiation Monitors with beam shut off capability• Beam current monitors in the LINAC• Additional supplementary shielding at the septum/stop (lead/poly)• Operating procedures for operators during injection
19 BROOKHAVEN SCIENCE ASSOCIATES
Storage Ring (Credible Radiation Incidents)
• 100 % injected beam from the booster to storage ring is lost at any location in the storage ring (15 nC/s is continuously lost at some location other than injection region)
Dose Rate = 300 mRem/h (3 mSv/h) (at the exterior of the experimental floor wall on contact)
• 100 % injected beam from the booster to storage ring is lost at any beamline front end due the shorting of a bending magnet (15 nC/s is continuously lost at a front end component)
Dose Rate = ~ 500 mRem/h (5 mSv/h) (at the exterior of the ratchet wall ~ 0.5 m from the FE) (peak bremsstrahlung shielded with shadow shields)
• 100% of stored beam is lost at a point - ~ 8 mRem (0.08 mSv)
Mitigation/controls to prevent significant exposure
• Area Radiation Monitors with beam shut off capability• Beam loss monitors inside the Storage Ring• Additional Supplementary Shielding (Shadow Shields)• Operating procedures for operators defining actions during injection
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Bulk Shielding Comparison
Bulk Shield at Experimental Floor Side
020406080
100120140
SOLEIL
DIAM
ONDAPS
BESSYII
ELETTRA
SPRING8
ESRF
NSLSII
Concrete
HD Concrete