Radiation Shielding Design of NSLS2

1 BROOKHAVEN SCIENCE ASSOCIATES

Radiation Shielding Design of NSLS2

P.K. Job

Conventional Facilities Advisory Committee Review

May 8 , 2007


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


Radiation Safety Review

• March 27 – 28, 2007

• Membership• S. Rokni (Chair) – SLAC• R. Donahue – ALS• P. Berkvens – ESRF• D. Beavis – BNL• C. Schaefer - BNL


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. “


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


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


Radiation Sources Consideredfor calculations

• Bremsstrahlung (High Energy Photons)

• Bremsstrahlung produced Neutrons

• Synchrotron Radiation (Low Energy x-rays)


Bulk Shielding Calculation Methodology


Dose Equivalent Factors used for Calculations(Thick Target Approximation)


Radiation Attenuation FactorsUsed in Calculations


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


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


LINAC Bulk Shielding Estimates


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.


Storage Ring Bulk Shielding Estimates


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


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


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


Bulk Shielding Comparison

Bulk Shield at Experimental Floor Side

020406080

100120140

SOLEIL

DIAMOND

APS

BESSYII

ELETTRA

SPRING8

ESRF

NSLSII

ConcreteHD Concrete

Radiation Shielding Design of NSLS2

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