Radioactivity Release at the Holifield Radioactive Ion Beam Facility

1. Radioactivity Release at the Holifield Radioactive Ion Beam Facility B. Alan Tatum 2009 DOE Accelerator Safety Workshop August 18-20, 2009 Brookhaven National Laboratory

2. Topics Description of HRIBF Overview of the July 2008 Radioactivity Release Response to the Event Key Corrective Actions Lessons Learned Summary Comments

3. 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.

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

5. HRIBF Post-accelerated Beams 175 RIB species available (+26 more unaccelerated) 32 proton-rich species 143 neutron-rich species Post-accelerated Intensity Beam list increased by ~50% since 2003

6. 25MV Tandem Electrostatic Accelerator Injector for Radioactive Ion Species 1 (IRIS1) Injector forStable Ion Species (ISIS) Oak Ridge Isochronous Cyclotron (ORIC) Enge Spectrograph 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

7. 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

8. 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 IRIS1 IRIS2 UC Target IRIS2 Target/Ion Source

9. 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.

10. Overview of the July 2008 Radioactivity Release Monday morning, July 28, 2008 Experiment in progress: ORIC providing 12A 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

11. 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

12. 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.

13. 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: 2.2x10-3mCi/ml (512 DAC) Concentration of activity outside door: 1.2x10-5mCi/ml (3.2 DAC)

14. IRIS1 Vacuum System No loss of high vacuum (~10-7 Torr during event) Leak on exhaust side of RP1 (at ~ atmospheric pressure)

15. Roughing Pump Oil-fill Plugs RP1 Oil-fill plug after event, before cleaning RP1 (right) and RP2 Oil-fill plugs after cleaning

16. IRIS1 Ventilation 13k 2 2 2 2 13k Supply • Supply is single 17,000 cfm fan • Distribution by duct sizing • Exhausts are 3 separate fans Exhaust

17. IRIS1 Ventilation 13k 2 2 2 2 13k Supply • Supply is single 17,000 cfm fan • Distribution by duct sizing • Exhausts are 3 separate fans Exhaust

18. 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.

19. 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.

20. 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

21. 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.

22. Oak Ridge National Laboratory:Meeting the challenges of the 21st century www.ornl.gov