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OPG

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... is used because the heavy hydrogen (deuterium) atoms in heavy water don't tend ... Deuterium atoms (hydrogen atom with 1 proton and 1 neutron in its nucleus) ... – PowerPoint PPT presentation

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Title: OPG


1
Transportation of Tritiated Heavy Water to
Darlington
CAC Meeting May 20, 2008
2
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

3
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?

4
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

5
Fission Process Begins
Incoming thermal (slow) Neutron
U-235 atom
6
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

7
Fission Process
Emitted Neutron
Gamma rays
Fission Product
Emitted Neutron
Emitted Neutron
Fission Product
8
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)
9
Tritium Formation Process
Incoming Neutron
Heavy Water Molecule
Deuterium atoms (hydrogen atom with 1 proton and
1 neutron in its nucleus)
10
Tritiated Heavy Water
Oxygen atom
Tritium atom Half-life 12.3 yrs
Deuterium atom
11
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

12
(No Transcript)
13
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

14
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

15
(No Transcript)
16
TDO Packages on Trailer
17
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

18
TDO Package Cross-section
Volume 5000 L Weight Dry 11,000 kg
Filled 16,300 kg Diameter 2.4 m Height
2.7 m
19
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

20
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?

21
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.
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