Radioactivity Release at the

Holifield Radioactive Ion Beam Facility

B. Alan Tatum

2009 DOE Accelerator Safety Workshop

August 18-20, 2009

Brookhaven National Laboratory

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Topics

• Description of HRIBF

• Overview of the July 2008 Radioactivity Release

• Response to the Event

• Key Corrective Actions

• Lessons Learned

• Summary Comments

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Holifield Radioactive Ion Beam Facility•The principal mission of the HRIBF, commissioned in 1996, is the

production of high quality beams of short-lived radioactive isotopes to support research in nuclear structure physics and nuclear astrophysics.

•HRIBF is currently unique worldwide in its ability to provide neutron-rich fission fragment beams post-accelerated to energies above the Coulomb barrier for reactions.

•HRIBF is based on two accelerators, one for production of radioactive species (ORIC) and one for post-acceleration (25 MV Tandem), that were part of a pre-existing complex (HHIRF) at ORNL:

• Oak Ridge Isochronous Cyclotron (ORIC)

• commissioned in 1963, but extensively renovated

• first used as a stand-alone light ion accelerator

• served as a booster accelerator for the Holifield Heavy Ion Research Facility (HHIRF)

• now serves as the driver accelerator for RIB production

• 25 MV Tandem Electrostatic Accelerator

• commissioned in 1982 for the HHIRF

• largest accelerator of its type in the world

• now serves as the RIB post-accelerator

•HRIBF is funded by the DOE Office of Nuclear Physics.

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Radioactive Ion Beams (RIBs) are Produced by the Isotope Separator On-Line (ISOL) Technique

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HRIBF Post-accelerated Beams

175 RIB species available 175 RIB species available (+26 more unaccelerated)(+26 more unaccelerated)32 proton-rich species32 proton-rich species143 neutron-rich species143 neutron-rich species

Post-accelerated IntensityPost-accelerated Intensity

Beam list increased by ~50% since 2003Beam list increased by ~50% since 2003

HRIBF S&T Review 2008HRIBF S&T Review 2008

Recoil Mass Spectrometer (RMS): nuclear structure endstation

Injector for Radioactive Ion Species 1 (IRIS1)

25MV Tandem Electrostatic Accelerator

Daresbury Recoil Separator (DRS): nuclear astrophysics endstation

Oak Ridge Isochronous Cyclotron (ORIC)

On-Line Test Facility (OLTF)

High Power Target Laboratory (HPTL)

& IRIS2

Injector for Stable Ion Species (ISIS)

Enge Spectrograph

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HRIBF Accelerator Specifications

• ORlC Light-Ion Beam Parameters

– Protons 55 MeV 50uA

– Deuterons 50 MeV 25uA

– 3He 133MeV 10uA

– 4He 100 MeV 10uA

• Tandem Accelerator Operating Parameters

– Ion mass 1 amu through 250 amu

– Maximum beam power 175 Watts

– Injected ion energy 150 keV-300 keV

– Terminal operating potential ~1 MV - 25.0 MV

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Injectors for Radioactive Ion Species 1&2

• High voltage platform systems biased to +/- 200kV

• Provides necessary energy and negative ions for injecting into the 25MV tandem accelerator

• Target/ion source assembly resides on the platform and is biased to +/-60kV

• Targets include hafnium oxide and pressed powder uranium carbide

IRIS1IRIS1

IRIS2IRIS2

IRIS2IRIS2

UC UC TargetTarget Target/Ion SourceTarget/Ion Source

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HRIBF Safety Documentation• Although the concept of hazard classification is no longer required by the Accelerator Safety Order DOE 420.2B,

HRIBF was approved by DOE as a “Low Hazard” facility as a result of the hazard screening documented in HS/6000/F/1/R1.

• The 46-year range of commissioning dates is reflective of the dynamic nature of the facility.

• The HRIBF ASE

– Establishes the envelope for safe operations

– Compliant w/ Order 420.2B and consistent w/ Implementation Guide

– Addresses Credited Controls identified in SAD

– Current revision date is July 2005. Presently being updated to incorporate IRIS2 and event corrective actions.

Accelerator Commissioning Date IRIS2 - 2009 HPTL - 2006 HRIBF - 1996 HHIRF - 1982 ORIC - 1963

Date of Preliminary Hazard Screening HS/6000/F/1/R1, May 1994 Date of SAD(s) and coverage SA/6000/RO-PHYS/R1, July 2005

SA/6000/RO-PHYS/R0 Aug 1996 SA/6000-PHYS/PHYS/R1, Sept 1994 ORNL/CF-81/330-R1, Jan 1982

Date of ASE Approval (s) and coverage ASE/6000/RO-PHYS/R1, July 2005 ASE/6000/RO-PHYS/R0, Aug 1996 ASE/6000-PHYS/PHYS/R2, Aug 1995 ASE/6000-PHYS/PHYS/R1, Sept 1994

Date of Exemption request approval NA

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Overview of the July 2008 Radioactivity Release• Monday morning, July 28, 2008

– Experiment in progress: ORIC providing 12A of 50 MeV protons to an IRIS1 UCx target for production of neutron-rich 81Zn delivered to new LeRIBSS facility

– Elevated radiation levels were detected outside the IRIS1 RIB production vault

– Maximum dose rate: 4 mrem/h

– Transferable contamination found in same area

• Building 6000 was evacuated as a precaution

• Operational Emergency declared by ORNL

• Electronic dosimeters of experimenters collected

• TLD’s of all 71 people who entered Bldg 6000 July 25-28 collected/read

• Six individuals sent for whole body count (all negative)

• No evidence of any measurable exposure was found

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Response to the Radioactivity Release

• A Management Investigation was chartered by ORNL• HRIBF and other ORNL staff designated as Recovery Team

– Throughout the investigation the Recovery Team:• Provided information to investigation team• Carried out physical examination of hardware involved

• Report of investigation team released in late November• Based on Judgments of Need in the investigation report, a

Corrective Action Plan was developed in December by HRIBF staff in consultation with ORNL management and the investigation team

• HRIBF developed a phased restart plan and mapped it to Corrective Actions

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Phased Restart• Stable beam operation: resumed September 2008.• On-line Test Facility (OLTF) operation with non-uranium targets

(nA scale production): January 2009. (OLTF is a facility for testing target and ion source systems with low intensity driver beams.)

• Batch mode operation at IRIS1: February 2009. (IRIS1 is the RIB production facility in C111S).

• High power target lab (HPTL) operation with non-uranium targets: May 2009. (HPTL is high-intensity driver counterpart of OLTF).

• Proton-rich RIB production at IRIS1 or testing at HPTL: May 2009• OLTF operation with uranium targets: June 2009.• Full operation of HRIBF including neutron-rich beam delivery

(uranium targets): June 2009.

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What happened?• Two-fold failure

– Leak in off-gas system• Pin-hole leak in roughing pump oil-fill plug.• Resulted from corrosion of plug

– Stamped carbon steel ~1mm thick, threaded

– Failure of shielded vault HVAC system• Belt driving 13,000 cfm exhaust fan failed• Interlock was based on motor operation, not on fan itself • Resulted in slight ( 3x10-4 atmosphere) positive pressure in shielded vaults• Consequent leakage of hot off-gas out of vault (~2 liter/s leak rate)

• Subsequent analysis determined 100% of released activity accounted for by noble gases (Xe and Kr isotopes)

• Total noble gas inventory:• Concentration of activity in C111S: 2.2x10-3 Ci/ml (512 DAC)• Concentration of activity outside door: 1.2x10-5 Ci/ml (3.2 DAC)

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IRIS1 Vacuum System

• No loss of high vacuum (~10-7 Torr during event)

• Leak on exhaust side of RP1 (at ~ atmospheric pressure)

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Roughing Pump Oil-fill Plugs

RP1 Oil-fill plug after event, before RP1 Oil-fill plug after event, before cleaningcleaning

RP1 (right) and RP2 Oil-fill plugs after RP1 (right) and RP2 Oil-fill plugs after cleaningcleaning

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IRIS1 Ventilation Supply

Exhaust

13k2 2

2 2

13k

• Supply is single 17,000 cfm fan

– Distribution by duct sizing

• Exhausts are 3 separate fans

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IRIS1 Ventilation Supply

Exhaust

13k2 2

2 2

13k

• Supply is single 17,000 cfm fan

– Distribution by duct sizing

• Exhausts are 3 separate fans

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Key Correctives Implemented• Differential pressure interlocks on HVAC system

– Important new engineered control - but does not rise to the level of a credited control (as per Accelerator Safety Order 420.2B)

• Enhanced surveillance program by Radiological Protection staff

• Enhanced maintenance program– More frequent inspection and regular replacement of pumps and other critical

components

• Developed revised and expanded Safety Assessment Document– Corrective action, ASRC review, incorporation of IRIS2

Additional Actions• Will proactively institute monitoring of HVAC exhaust stacks for the RIB

production vaults (IRIS1, IRIS2) for airborne radioactivity– Intended as early warning, not safety system or a quantitative monitor of releases.

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Thorough response recognized by DOE Office of Enforcement

• Letter received from Office of Enforcement May 13th

• The Office has elected not to pursue investigation recognizing “the comprehensive scope of your investigation and corrective actions”

• Extent of Condition Review has been completed.

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Lessons Learned• Maintenance: periodically review PM schedules to ensure that

– all equipment is on the list

– maintenance frequency is appropriate

– instructions are clear and complete

– PM results are recorded

• Radiological surveillance – Ensure that a rigorous plan is in place

– Review the plan regularly to ensure that it will effectively identify off-normal conditions

• Expand SAD to include all plausible accident scenarios

• Ensure that lab emergency response personnel have access to appropriate facility information

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Summary Comments• The July 2008 Operational Emergency dominated our

effort and our attention in FY2009. • The most important fact concerning this event was that

nobody received a measurable radiological dose.• The phased restart that we were able to execute allowed

us to continue to produce exciting science while waiting for neutron-rich operation, but nevertheless, events such as this are always detrimental to research programs.

• We believe we have learned a great deal from this regrettable occurrence, and have taken measures to reduce the likelihood of recurrence.

• I hope that this information will be of assistance to you as we all strive for continuous improvement in safe operation of our facilities.

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