Radioactivity Release at the Holifield Radioactive Ion Beam Facility. B. Alan Tatum. 2009 DOE Accelerator Safety Workshop August 18-20, 2009 Brookhaven National Laboratory. Topics. Description of HRIBF Overview of the July 2008 Radioactivity Release Response to the Event
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B. Alan Tatum
2009 DOE Accelerator Safety Workshop
August 18-20, 2009
Brookhaven National Laboratory
Description of HRIBF
Overview of the July 2008 Radioactivity Release
Response to the Event
Key Corrective Actions
175 RIB species available
(+26 more unaccelerated)
32 proton-rich species
143 neutron-rich species
Beam list increased by ~50% since 2003
25MV Tandem Electrostatic Accelerator Separator On-Line (ISOL) Technique
Injector for Radioactive Ion Species 1 (IRIS1)
Injector forStable Ion Species (ISIS)
Oak Ridge Isochronous Cyclotron (ORIC)
Daresbury Recoil Separator (DRS): nuclear astrophysics endstation
High Power Target Laboratory (HPTL) & IRIS2
Recoil Mass Spectrometer (RMS): nuclear structure endstation
On-Line Test Facility (OLTF)
HRIBF S&T Review 2008
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
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
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.
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
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
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.
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: 2.2x10-3mCi/ml (512 DAC)
Concentration of activity outside door: 1.2x10-5mCi/ml (3.2 DAC)
No loss of high vacuum (~10-7 Torr during event)
Leak on exhaust side of RP1 (at ~ atmospheric pressure)
RP1 Oil-fill plug after event, before cleaning
RP1 (right) and RP2 Oil-fill plugs after cleaning
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
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.
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
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
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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