Radiation Shielding Design of NSLS2

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Radiation Shielding Design of NSLS2

P.K. Job

Conventional Facilities Advisory Committee Review

May 8 , 2007

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Preliminary Shielding Design Documents

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 Review

• 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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Radiation Safety Review

• 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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Radiation Sources Consideredfor calculations

• Bremsstrahlung (High Energy Photons)

• Bremsstrahlung produced Neutrons

• Synchrotron Radiation (Low Energy x-rays)

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Bulk Shielding Calculation Methodology

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Dose Equivalent Factors used for Calculations(Thick Target Approximation)

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Radiation Attenuation FactorsUsed in Calculations

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Accelerator Operating Conditions used in Calculations

• Linac• 200 MeV• 20 nA

• Booster• 3.5 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 during Normal Operations

• Linac – 1% distributed loss at 200 MeV

• Linac to Booster injection efficiency – 50%

• Booster losses – 2% loss at any point at 3.5 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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Storage Ring Bulk Shielding Estimates

Concrete Thickness Vs. Distance (Storage Ring)

0

0.2

0.4

0.6

0.8

1

1.2

0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4

Distance of the wall from Ring

Dos

e R

ate

(mre

m/h

) 80 cm 90 cm100 cm110 cm 0.25 mrem/h0.5 mrem/h70 cm

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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

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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 (4 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

DIAMOND

APS

BESSYII

ELETTRA

SPRING8

ESRF

NSLSII

ConcreteHD Concrete