Ali Leilabadi

1

Tritium Emission Reduction at DTRF Using a
Bubbler System

• Ali Leilabadi
• Sr. Technical Engineer
• OPG Darlington Tritium Removal Facility

2
Problem Description

• Tritiated Feed to DTRF on Jan 20th 2004,
  following extended shutdown going back to Mar
  2003.
• First Batch of elemental T2 product withdrawn
  from the High Tritium Distillation (HTD) system
  on Jan 27th.
• T2 removed via transfer line, protected by
  rupture disc relief valve, to Tritium
  Immobilization system (TIS).

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Problem Description

• Rupture disc failed during first draw-off from
  the HTD. Follow-up investigation showed manual
  valve on bypass line around rupture disc was
  passing
• Resulting in release of T2 into the relief valve
  discharge line, which ties into the contaminated
  exhaust system.

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Problem Description

• Relief valve discharge line is a 2 line with 31
  metre of dead space before it ties into the
  exhaust of TRF Ventilation fans.
• By design relies on the diffusion of stagnant gas
  into the turbulent flow of the vent system to
  remove any T2 held up in line.

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Problem Description

• Controlled helium purge was conducted on Feb 11
  2004. Purge terminated after 3 minutes, when, as
  evident from online monitor, the backout limit
  would be reached.
• Subsequent Compliance monitor results, from Feb
  12th to 14th, indicated that a significant amount
  of T2 and T2O had been released due to purge

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Plant Conditions

• Tritium oxide attributed to
• the conversion of elemental tritium to tritium
  oxide in the presence of the stainless steel
  metal (metal surface catalyzed reaction occurs
  relatively quickly)
• the exchange of elemental tritium with water to
  produce tritium oxide (gas phase reaction
  extremely slow) (ref 1)

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Tritium Immobilization System and Ventilation
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Plant Conditions

• Due to Tritium oxide and elemental tritium in
  vent line, it was no longer possible to purge.
• More tritium oxide is formed, the longer the
  elemental tritium remains in the line.
• During the 15 years of operation, the TIS vent
  line exposed to pure tritium gas a few times
  (intermittently), prior to this event.

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Plant Conditions

• Recent as well as past, tritium exposures have
  contributed to the total inventory on the vent
  line surface.
• Not possible to predict with any degree of
  certainty, the tritium inventory on the Vent line
  surface.
• Therefore, no longer able to purge vent line, and
  alternate means of recovering tritium in line was
  needed.

10
Equipment

• Team put together to look at options of removing
  tritium in discharge line
• Preferred option to construct a Tritium Recovery
  Rig (Bubbler system), to remove and recover as
  much as possible the elemental and oxide forms of
  tritium and minimize continued significant
  tritium releases.

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Equipment

• Rig consists of the following equipment
• Flow meter to measure the Vent Line purge air
  flow rate
• Two 45 gallon drums (Drum 1 and Drum 2) filled
  with 150 Kg demineralized water
• BOT stack monitoring equipment consisting of a
  vacuum pump and a catalytic recombiner (without
  the Silica Gel cartridges), located between the
  two drums.
• Flow meter to measure ambient air flow rate into
  the BOT equipment.
• 3/8 SS tubing fabricated as sparger with drilled
  holes, placed inside drum to enhance mass
  transfer between oxide and water.

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Recovery Process

• Moist air from the stack drawn through vent line
  by the BOT vacuum pump via slightly opened valve
  and into Drum 1.
• Most of the Tritium oxide is scrubbed and
  collected in the water.
• Air than drawn through BOT, where any elemental
  tritium in the purge air is converted to tritium
  oxide by the BOT catalytic recombiner.
• This oxide is then scrubbed and collected in the
  water of the 2nd Drum. Purge air then is sent to
  ventilation system, free of tritium.

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Recovery Process

• Tritium collected in Drum 1 represents tritium
  oxide removed from the Vent line.
• Tritium collected in Drum 2 represents elemental
  tritium removed from the Vent line.

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Recovery Process

• Provision for sampling included in Recovery Rig
  construction.
• When tritium concentration approached 7 Ci/kg in
  Drum, the drum would be safely removed and
  stored, and a new drum of demineralized water was
  placed in service.
• Helium purge connection before sampling or
  changeout of drum, to minimize any tritium
  release to room.
• Also, helium leak check performed for each drum
  changeout to ensure leak tightness to 1 X 10-4
  cc/sec.

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Recovery Process

• Tritiated water produced from Recovery Rig needs
  to be disposed of in a safe manner.
• Tritiated water was subsequently pumped out of
  drum and directed to DTRFs downgraded D2O
  system.

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Results

• Approx. 3500 Ci Tritium oxide collected in Drum
  1 and Approx. 230 Ci Elemental tritium collected
  in Drum 2, from Early March 2004 to April 2004.
• Significant quantity of tritium release as a
  result of blown rupture disc has been in the
  oxide form.
• Consistent with experimental work conducted at
  AECL Research, which indicate that stainless
  steels exposed to elemental tritium will release
  90 of their tritiated species in the oxide form
  during desorption of the metal surface. (most
  likely conversion of HT to HTO by surface
  reactions) (ref 3)

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Problems Encountered

• Tritium surface contamination
• Tritium releases to room when rig is in service
• Changing drums,
• Sampling drums,
• removing caps,
• leak tightness of Rig piping
• Several evolutions of Recovery Rig before
  optimizing setup (Essentially a Research Project)
• Adding more valves
• Provision for scintrex and helium hook up
• Added flexible lines and quick connects to
  facilitate changing of drums

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Future Work

• Leak tightness of Rig improved by using
  appropriate fittings and flexible lines
• Smaller more compact and Mobile unit on a skid,
  to facilitate hooking up unit as needed.
• Increase purge flow rate (ie. larger pump) to
  increase capture of tritium. (BOT pump currently
  limited to 150 ml/min)

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References

• DTRF Tritium Immobilization System (TIS) Vent
  Line Purge (RD407) For Tritium Recovery (March,
  April 2004), K.M. Kalyanam June 2004.
• "A Review of Tritium Gas Interactions with
  Stainless Steel Surfaces", D. F. Mullins, OHRD
  Report No. 92-21-K, April, 1992.
• "Sorption of Tritium and Tritiated Water on
  Construction Materials", R.S. Dickson and J.M.
  Miller, Fusion Technology, Vol. 21, March 1992.

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Contributors

• Ali Leilabadi, Engineering
• Omar El-Behairy, Engineering
• Denny Williams, Engineering
• Thomas Wong, Engineering
• Kaly Kalyanam, Design Engineering
• Harold Vogt, Design Engineering
• Steve Hackett, Operations
• Peter Smith, Operations
• Art Reid, Operations
• Ken Ringrose, Radiation Protection
• Bruce Haslehurst, Mechanical Maintenance
• James Mcfarlane, Mechanical Maintenance
• Rob Will, Control Maintenance
• Clinton Young, Control Maintenance
• Aaron Gaudon, Control Maintenance
• Tonnie Debruijn, Components and Equipment