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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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radioactivity release at the holifield radioactive ion beam facility

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
Topics

Description of HRIBF

Overview of the July 2008 Radioactivity Release

Response to the Event

Key Corrective Actions

Lessons Learned

Summary Comments

slide3
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.
hribf post accelerated beams
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

slide6
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

hribf accelerator specifications
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

injectors for radioactive ion species 1 2
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

hribf safety documentation
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.

overview of the july 2008 radioactivity release
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

response to the radioactivity release
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

phased restart
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.

what happened
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)

iris1 vacuum system
IRIS1 Vacuum System

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

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

roughing pump oil fill plugs
Roughing Pump Oil-fill Plugs

RP1 Oil-fill plug after event, before cleaning

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

iris1 ventilation
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

iris1 ventilation1
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

key correctives implemented
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.
thorough response recognized by doe office of enforcement
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.

lessons learned
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

summary comments
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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