CAC MeetingMay 20, 2008

Transportation of Tritiated Heavy Water

to Darlington

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

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?

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 don’t tend to absorb neutrons like light hydrogen atoms

Fission Process Begins

Incoming thermal (slow)

Neutron

U-235 atom

To Fission or Not to Fission

82 % of the excited form of U-236 created by neutron absorption fissions quickly

18 % emit a gamma ray and remain as U-236

U-236 (excited after neutron absorption)

Fission Process

EmittedNeutron

Fission Product

Fission Product

EmittedNeutron

EmittedNeutron

Gamma rays

Heavy water slows neutrons

Incoming“fast” Neutron Heavy Water

Molecule

Deuterium atoms

(hydrogen atom with 1 proton and 1 neutron in its nucleus)

Oxygen atom

Deflected“slower” Neutron

Tritium Formation Process

IncomingNeutron Heavy Water

Molecule

Deuterium atoms

(hydrogen atom with 1 proton and 1 neutron in its nucleus)

Tritiated Heavy Water

Deuterium atomTritium atom

Half-life 12.3 yrs

Oxygen atom

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

PN5-8 H3 Emissions and Moderator H3 Concentration

0

2000

4000

6000

8000

10000

12000

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

H3 E

mis

sio

ns (

Ci/

yr)

0

5

10

15

20

25

Mo

d H

3 C

on

ce

ntr

ati

on

(C

i/kg

)

Tritium Emission Ci

PB Mod Ci/kg

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

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

TDO Packages on Trailer

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

TDO Package

Cross-section

Volume: 5000 L

Weight

Dry: 11,000 kg

Filled: 16,300 kg

Diameter: 2.4 m

Height: 2.7 m

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

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?

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.