Why has Greenpeace made a submission to the Canadian Nuclear
Safety Commission (CNSC) ?
On Wednesday May 14 the CNSC is holding a hearing on Ontario
Power Generation's (OPG) proposal to renew its licence for the
Pickering B nuclear station for five more years.
Greenpeace is concerned that the accident risks at the station
are increasing because of ageing, deteriorating reactor components
and the recent disclosure that previous safety studies are no
longer valid.
Greenpeace is asking the CNSC to more strictly control the
ageing Pickering reactors during the last years of its operational
life.
Why is Greenpeace particularly concerned by safety of the
Pickering Nuclear Station?
Because of its design flaws, age and location, the Pickering
Nuclear station is arguably Canada's most dangerous nuclear
station. Pickering is also ageing and its components are
deteriorating.
Just 30 km from downtown Toronto, Pickering is closer than any
other nuclear station in the world to a major population centre.
Approximately 2.5 million people live within 30 km of the Pickering
reactors.
Regulatory authorities would not allow a new plant to be built
at Pickering today because of the high population density.
What should happen to the Pickering Nuclear Station?
Greenpeace believes that Pickering should be shut down.
Four of the six reactors at Pickering require billions of
dollars in repairs, otherwise they cannot operate past 2014. The
McGuinty government, however, has directed OPG to develop a plan to
rebuild and extend the life of the station until 2060. The
government will make a decision on Pickering's future in early
2009.
Instead of wasting time and money developing plans to rebuild
the ageing nuclear station, the McGuinty government should develop
safe and clean energy options to replace the electricity produced
by Pickering when it shuts down in 2014 for either expensive
repairs or permanent closure.
Before Pickering must shut down in 2014 what should happen to
the station?
Greenpeace is asking the CNSC to more strictly control the
operation of the Pickering reactors and prepare for its closure
their 2014.
Specifically, Greenpeace is asking that:
- The CNSC deny OPG's request for a 5-year licence. Instead,
Greenpeace is asking for a shorter 2-year licence to allow for more
public scrutiny of the station.
- The CNSC proactively release all information on the condition
of the ageing reactor components and accidents.
- The CNSC require OPG to develop a plan for closing the
station.
- The CNSC implement precautionary measures, such as lowering the
output from the station (known as de-rating), to protect against
and mitigate recent findings on the declining safety of the
reactors.
What are Pickering's design flaws?
Pickering has two significant design flaws that increase the
risk of accidents.
First, Pickering is the only nuclear station in the world that
allows multiple reactors to share important safety systems - the
Emergency Coolant Injection System and the containment system -
that are intended to control the release of radioactivity in the
case of an accident.
Second, the CANDU design of the Pickering nuclear station shares
an inherent design flaw with the Chernobyl-style RBMK reactor
design called "the positive void coefficient" that can lead to an
explosive pulse of power.
Why do shared safety systems at the Pickering nuclear station
increase accident risks?
Currently, there are six operating reactors at the Pickering
nuclear station - two at the older Pickering "A" station and four
at the Pickering "B" station.
Since the Pickering reactors share safety systems, there is
reduced redundancy, meaning that more than one accident happening
at the same time could have catastrophic consequences.
Are multi-reactor accidents possible?
Yes. In documents acquired by Greenpeace, Canadian Nuclear
Safety Commission (CNSC) staff say such accidents are possible.
They describe a multi-accident reactor accident in the following
way:
"At Pickering B some initiating events could produce multiunit
accidents. For instance, a medium or large steam line break event
at one unit might produce a harsh environment in the common
powerhouse leading to common cause accidents at all units with
multiple failures of mitigating systems. Since these types of
accidents are major contributors to the plant risk according to PRA
[Probabilistic Risk Assessment] results, additional risk from
adjacent units may not be negligible. Furthermore, if multiple
mitigating systems fails due to the harsh environment, several
units may have severe core damage simultaneously. This may create
such a challenge to the containment that its failure may not be
precluded."
What is the "positive void coefficient"?
The positive void effect was an important contributor to the
1986 Chernobyl accident.
A positive void effect refers to the rapid increase in reactor
power that occurs when voids form in the coolant that is used to
remove heat from the reactor core. The increase in reactor power
makes it difficult to control the reactor increasing the chance of
an explosion and release of radioactivity.
CANDU reactors - like those at the Pickering nuclear station -
share this inherent design flaw with the Chernobyl RBMK reactor
design.
Are there any reasons to be more concerned by the "positive
void coefficient" now than previously?
Yes. Internal CNSC documents acquired by Greenpeace show that
the magnitude of positive void coefficient at Pickering B is worse
than previously thought.
According to CNSC staff "…the new analysis indicates a
significant change in the licensing case results and large
reduction of the previously reported safety margins…".
Because the positive void effect was an important contributor to
the Chernobyl accident, international safety standards have moved
to ban reactor designs with positive void..
Nuclear regulators would not permit the construction and
operation of the Pickering reactors today because of the danger
posed by positive void.
Because the magnitude of positive void effect in the Pickering B
reactors has been discovered to be more significant than previously
thought, Greenpeace is requesting that the CNSC implement
precautionary measures, such as lowering the output from the
station (known as de-rating), to mitigate the declining level of
safety at the station.
Why is the age of the Pickering nuclear station a concern?
The Pickering nuclear station is the oldest nuclear station in
Canada.
Given the complexity of a nuclear plant, the impacts of ageing
are not well understood and often only become apparent after
component failures.
The four reactors at the Pickering "A" nuclear station went into
service starting in 1971. Two of the Pickering A reactors were
recently restarted after billions of dollars in repairs while two
have permanently shut down.
The four Pickering "B" reactors went into service starting in
1983. Ontario Power Generation (OPG) the four Pickering "B" will
reach the end of their operational life in 2014.
Why is the location of Pickering a concern?
There are over 2.5 million people within 30 km of the Pickering
nuclear station.
Regulatory authorities would not allow a new plant to be built
at Pickering today because of the high population density
nearby.
After the Chernobyl accident in Ukraine in 1986, a 30 km area
around the station was permanently depopulated. There are currently
4,057,745 people within 50 kilometers of the Pickering.
A Chernobyl-scale accident at the Pickering Nuclear Station
would have a devastating impact on the health and environment of
Southern Ontario and demolish the economy of Canada's largest city,
Toronto.