OPG

1
Transportation of Tritiated Heavy Water to
Darlington
CAC Meeting May 20, 2008
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Presentation Plan

• Issue raised by Community Working Group
• Why do we have tritium?
• Why is tritiated heavy water shipped to
  Darlington?
• How is tritiated heavy water shipped to
  Darlington?
• Have there ever been public exposures as a result
  of shipment?
• Issue resolution

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Issue 122 Biophysical effects of tritiated water
from Pickering NGS sent to the Darlington Tritium
Removal Facility

• Why and how does PNGS ship tritiated water to
  Darlington Tritium Removal Facility (Darlington)?
• At any time during its shipment, are members of
  the public exposed to unsafe radiation levels?

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Why do we use Heavy Water?

• Both the moderator system and the primary heat
  transport systems are filled with heavy water
• It is used to slow fast neutrons down
• It is used because the heavy hydrogen (deuterium)
  atoms in heavy water dont tend to absorb
  neutrons like light hydrogen atoms

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Fission Process Begins
Incoming thermal (slow) Neutron
U-235 atom
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To Fission or Not to Fission
U-236 (excited after neutron absorption)

• 82 of the excited form of U-236 created by
  neutron absorption fissions quickly
• 18 emit a gamma ray and remain as U-236

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Fission Process
Emitted Neutron
Gamma rays
Fission Product
Emitted Neutron
Emitted Neutron
Fission Product
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Heavy water slows neutrons
Oxygen atom
Incoming fast Neutron
Heavy Water Molecule
Deflected slower Neutron
Deuterium atoms (hydrogen atom with 1 proton and
1 neutron in its nucleus)
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Tritium Formation Process
Incoming Neutron
Heavy Water Molecule
Deuterium atoms (hydrogen atom with 1 proton and
1 neutron in its nucleus)
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Tritiated Heavy Water
Oxygen atom
Tritium atom Half-life 12.3 yrs
Deuterium atom
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Why do we want to get rid of tritium?

• It is radioactive.
• In the form of tritiated heavy water it is taken
  into the body both through the skin and via
  respiration.
• It builds up in the moderator and heat transport
  systems with continued operation
• Workers are exposed to tritiated heavy water that
  escapes station systems
• Higher worker dose
• More protective equipment must be worn
• Public is exposed via air and waterborne
  emissions from the station

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Why do we ship it to Darlington Station?

• The Darlington tritium removal facility partially
  removes the tritium from tritiated heavy water
• Tritium gas produced there is stored in special
  containers
• De-tritiated Heavy Water is returned to
  Pickering for re-use

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How do we ship it to Darlington Station?

• Inside specially designed transportation packages
  intended only for that usage
• Sealed
• Impact, fire and leak resistant
• The detritiated heavy water is returned using
  the same transport packages

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TDO Packages on Trailer
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How do we know shipping is safe?

• The design is verified as meeting CNSC (IAEA)
  requirements
• Impact test to simulate a vehicular accident
• 9 metre drop onto a solid target onto its weakest
  point
• Fire test to simulate a post vehicular accident
  fire
• 30 Minutes in 800 Degree Centigrade fire
• Leakage test
• 8 hour immersion at 15 metre depth or equivalent
• All three tests conducted in series

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TDO Package Cross-section
Volume 5000 L Weight Dry 11,000 kg
Filled 16,300 kg Diameter 2.4 m Height
2.7 m
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Has there ever been an unsafe exposure from
transportation of tritiated heavy water to and
from Darlington?

• No !
• The TDO package is monitored before departure and
  on arrival to make sure all applicable limits
  have been met
• There has never been event that involved a
  release during transit

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Issue 122 Biophysical effects of tritiated water
from Pickering NGS sent to the Darlington Tritium
Removal Facility

• Why and how does PNGS ship tritiated water to
  Darlington Tritium Removal Facility (Darlington)?
• At any time during its shipment, are members of
  the public exposed to unsafe radiation levels?

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Suggested Disposition

• Category 1
• No further action required, the issue has been
  dealt with to the extent required or the extent
  possible.
• or
• The issue is being managed satisfactorily and
  would be brought back to the CAC only if an
  unusual result or event arose calling into
  question the managed process for the issue.