April 14, 2008
Louise Levert
Commission Operations Officer
Canadian Nuclear Safety Commission
280 Slater St., P.O. Box 1046
Ottawa, Ontario
K1P 5S9
Fax: (613) 995-5086
Email:
Re: Recommendations regarding the proposed license renewal of
the Pickering B nuclear station
Dear Ms. Levert,
Thank you for the invitation to comment on the proposed licence
renewal for the Pickering B Nuclear Station.
Greenpeace was founded in Canada in 1971. Since then, Greenpeace
offices have opened in over 30 countries across the globe, with 2.8
million members internationally, including more than 88,000 members
in Canada. Greenpeace has had a long-standing interest in issues
relating to nuclear power plant operation.
Participation in this process should not be interpreted as an
endorsement of the Canadian Nuclear Safety Commission (CNSC) Rules
of Procedure for hearings. These rules are unfair to
public-interest intervenors due to the tight time restrictions
placed on presentations, the prohibition on presenting at both days
of two-day hearings, the lack of opportunity for interveners to
test evidence through cross examination, and the failure to provide
intervenor funding for expert testimony and other intervention
expenses.
Greenpeace would like to cite a few examples of the positive
improvements that public interventions have had on the CNSC's
oversight of the nuclear industry in Canada. Public intervenors,
for example, are often well placed to point to gaps or weaknesses
in the CNSC's regulatory approach. For example:
- In 2005, Greenpeace raised its concerns regarding the CNSC's ad
hoc approach to approving the life-extension of nuclear stations in
Canada. In 2006, Ian Grant, the CNSC's Director General of Power
Reactor Regulation, admitted that the publication of regulatory
guide G-360, Life Extension o. Nuclear Power Plants, was produced
due to Greenpeace's concerns.
- In a 2006 petition to the federal Environment Commissioner,
Greenpeace raised its concern that, unlike other nuclear
regulators, the CNSC had no system for classifying radioactive
wastes. Following the petition, CNSC staff acknowledged the need to
develop a classification system and the Commission ruled "…that a
clear classification system would bring added clarity to nuclear
waste categorization in Canada."
- At licence renewal hearings in 2006, Greenpeace exposed the
fact that neither New Brunswick Power nor Hydro-Quebec had a plan
for managing its non-fuel radioactive waste over the long-term.
Forced to respond to questions by the Commission spurred by
Greenpeace's concerns, CNSC staff committed to ask Hydro-Quebec "in
the days to come" to present a plan for managing these wastes.
These examples point to the ability of public-interest
intervenors to identify gaps or weaknesses in the CNSC's regulatory
approach. Although the CNSC is often initially defensive when
presented with these critiques, subsequent Commission efforts to
address these gaps and weaknesses in regulatory policy have led to
improved oversight of the nuclear industry in Canada.
1. Summary of Concerns and Principal Recommendations
Due to its design flaws and location, the Pickering Nuclear
Generating Station (PNGS) is arguably Canada's most dangerous
nuclear power station.
PNGS is also approaching the end of its operational life, a
period during which unpredictable component degradation will
increase the potential for accidents and unplanned shut-downs.
Concurrently, Ontario is facing an electricity shortage over the
next decade and is proposing to continue to operate Pickering B
past the date which Ontario Power Generation (OPG) would typically
consider it uneconomic to operate the station safely.
The pressure on OPG to ensure electricity supply while
minimizing the costs of maintaining ageing reactors is an obvious
motivation to operate at reduced safety margins. Given this,
Greenpeace is deeply concerned that the CNSC has no clear set of
criteria for determining the end-of-life of nuclear stations in
Canada. Without such transparent criteria the CNSC will be highly
vulnerable to back-room pressures to ageing reactors to continue
operating with reduced safety margins.
For these reasons, Greenpeace recommends the following:
- Given the uncertainties associated with the operational life of
the Pickering B Nuclear Station, Greenpeace Canada requests that
the Commission approve a 2 year license renewal instead of a 5 year
renewal.
- Given that there is a strong possibility that OPG may decide
not to rebuild the Pickering B nuclear station and that the four
reactors may be unable to operate until the stated end-of-life date
in 2014, Greenpeace Canada recommends that the CNSC include a
licence condition requiring OPG to develop an end-of-life plan for
the station.
- Given the current lack of end-of-life criteria and the
political pressures to maintain electricity supply post 2010,
Greenpeace Canada recommends that the Commission require OPG (as
well as other licencees) and CNSC staff to submit and report
annually on the fitness-for-service assessments and forecasts for
the life-limiting components for each of the nuclear stations in
Canada in its annual report on the performance of the Canadian
nuclear power industry. The Commission should also require OPG to
make available on request - outside of Access to Information - any
studies regarding fitness for service.
- Given the lack of a coherent approach to determining
end-of-life criteria, Greenpeace requests that the Commission
direct staff to develop an approach to the issue end-of-life
criteria. Staff should present their approach and research
regarding end-of-life criteria at a public meeting so that the
Commission and the public can evaluate whether staff are addressing
safety criteria related to ageing in a timely and precautionary
manner.
- Given the undue and untransparent input Atomic Energy of Canada
Limited (AECL) has had in influencing CNSC standards to accommodate
a fundamental design flaws of CANDU reactors, Greenpeace recommends
that the CNSC proactively release all internal documents and
correspondence from the "positive reactivity feedback working team"
which has been developing the CNSC's approach to dealing with the
positive void coefficient.
- Greenpeace requests that the Commission improve its disclosure
protocols and require the proactive release all safety studies,
including probabilistic risk assessments, deterministic safety
studies, hazards analysis and S-99 reports.
- Greenpeace requests that OPG and CNSC staff be required to
assess and report on the impacts of a large international
commercial aircraft crash at the Pickering nuclear station at a
public meeting of the CNSC.
- Given recent findings regarding the magnitude and impact of
positive void reactivity on the safety case for Pickering B, CNSC
staff should make recommendations regarding what precautionary
operational measures, such as de-rating the station, should be
taken to mitigate the uncertainties in Pickering B's safety
margins.
1. The End of Life of the Pickering B Nuclear Station:
Uncertainties & Vulnerabilities
OPG and CNSC staff are recommending a five-year licence renewal,
which, they claim, would fall a year before Pickering B's projected
end-of-life in 2014.
Greenpeace does not believe that there is adequate or
trustworthy information in the public domain for assessing the
safety case for operating the Pickering B reactors until 2013.
There are two reason for this: First, the CNSC's failure to develop
transparent end-of-life criteria for assessing the point at which
ageing reactors must be shut down; and second, the political and
business pressures on OPG to operate its ageing nuclear stations as
long as possible to fill Ontario's looming electricity gap.
OPG's end-of-life estimates for the Pickering B nuclear station
have changed significantly during the past three years. In 2006,
OPG changed the estimated end of life for the station from 2009 to
2014. In 2006 OPG also began the environmental and safety reviews
to decide whether it would rebuild or permanently close Pickering B
in 2014.
OPG, however, makes the claim in its submission for this licence
renewal that it can operate Pickering B past 2014, stating that:
"Based on current information and the life cycle management plans,
OPG's current view is that the units will operation for
approximately a further ten years." In 2006, however, OPG informed
Greenpeace that the end of service life for Pickering B units 5 - 7
was 2014 and that unit 8 would reach its end of service life in
2016.
As will be discussed, Greenpeace believes that OPG's operational
life projections for the Pickering B nuclear station are being
motivated by business and electricity supply pressures instead of
safety assessments.
Greenpeace believes that it is incumbent upon the CNSC to
obligate OPG to openly release all studies used to rationalize the
operational lives of its reactors. Furthermore, the Commission
should develop transparent criteria for assessing the end-of-life
of nuclear plants so that the public can assess OPG's safety
studies and the CNSC's oversight of ageing reactors.
2. CNSC Approach to Ageing and End-of-Life
The CNSC has no criteria for determining the end of life of
Canada's nuclear stations. Instead, the CNSC requires licencees to
demonstrate the "fitness-for-service" of its reactors through
near-term projections of component integrity.
Licencees, meanwhile, determine the operational life of their
reactors based on the ability of "life-limiting components" - such
as feeder pipes, pressure tubes and steam generators - to operate
while economically meeting safety goals established by the CNSC.
The operational life dates claimed by nuclear operators, then, have
not been assessed or approved by CNSC staff.
Greenpeace is deeply concerned that this lack of clear-cut
safety criteria for determining end-of-life leaves the CNSC
vulnerable to political pressures to keep ageing reactors with
declining safety margins operating to ensure electricity supply. It
also makes it difficult for public intervenors to assess the
adequacy of the safety case used to justify the continued operation
of ageing reactors.
It is noteworthy that the CNSC may have internally admitted the
need to develop such requirements. The CNSC's research program, for
instance, commissioned a study in 2007 to "define end-of-life
criteria" for pressure tubes. The study will evaluate "ageing
management plans; fitness-for-service criteria and technical data"
as well as "…the risks posed by the ageing processes."
Greenpeace believes the CNSC's preparation for the end-of-life
of Canada's nuclear stations is similar to the way it prepared to
oversee reactor life-extension proposals: ad hoc, uncoordinated and
without public input. Greenpeace believes that the Commission
should look at issues of reactor end-of-life comprehensively and
transparently to identify and address gaps and weaknesses in its
regulator approach.
Recommendation: Greenpeace requests that the Commission
direct staff to develop a gap analysis on the issue of end-of-life
criteria. Staff should present their approach and research
regarding end-of-life criteria at a public meeting so that the
Commission and the public can evaluate whether staff are addressing
safety criteria related to ageing in a timely and precautionary
manner.
3. Ontario's Electricity Gap: The Threat to Nuclear Safety
Without transparent end-of-life criteria and public scrutiny of
OPG's assessments regarding the projected end-of-life of its
nuclear stations, Greenpeace believes the CNSC will be vulnerable
political pressure to allow ageing reactors with declining safety
margins to continue operating in order to ensure electricity
supply.
Greenpeace has raised its concern before that Ontario's looming
electricity supply crunch will exert pressure on licensees, and
subsequently on the CNSC, to make guaranteeing electricity supply a
priority over safety in the coming decade. The CNSC has yet to
respond to Greenpeace's concerns.
As mentioned in past submissions, Greenpeace is concerned that
the Ontario Power Authority (OPA), which is responsible for the
province's electricity planning, is calling for the "Sequencing
[emphasis added] of refurbishments, given that many of the reactors
currently in service will require refurbishment within a narrow
time window, and that there is limited technical capability
available province wide for refurbishment."
Greenpeace has requested that the OPA release its schedule for
reactor shut down and refurbishment used in its Integrated Power
System Plan (IPSP). Given that nuclear generation provides 50% of
Ontario's electricity supply, the ability of Ontario's nuclear
operators to meet the OPA's proposed schedule will be essential to
maintaining adequate electricity supply after 2010 if alternative
are not developed. The OPA, however, has refused to release this
schedule.
The OPA's mandate is to ensure electricity supply, not nuclear
safety. The OPA, then, will have an obvious motivation to cut
corners, speed up refurbishment projects and run reactors longer
than would be otherwise deemed safe.
Notably, OPG has revised its end-of-life estimates based on the
electricity planning estimates of the OPA. OPG states, for
instance, in its 2007 annual report that "The Company has extended
the service life of Bruce B nuclear generating station to 2014 for
depreciation purposes effective January 1, 2008 after reviewing
future capacity plans in the OPA's IPSP [emphasis added], and
historical information regarding the service lives of major life
limiting components of the station."
The OPA has also proposed "service extensions to some or all of
the Pickering B Units" until new reactors can come online post 2019
if a decision is made not to rebuild the Pickering B nuclear
station. The OPA states that reactor lives are "determined by the
technical or economic end-of-life of major components such as
nuclear channels, feeder pipes and/or steam generators." It makes
no mention, however, of increased safety risks associated with
running ageing reactors.
Evidence of the influence of this proposition is reflected in
the following claim made in OPG's submission: "…OPG's current view
is that the units will operate for approximately a further ten
years."
Greenpeace opposes proposals for service extensions at Ontario's
nuclear stations. Moreover, Greenpeace is concerned that the OPA's
and OPG's proposals for service extension as well as revised claims
of reactor life-span are being presented unquestioned and
unverified from a safety perspective.
The recent firing of CNSC president Linda Keen shows that
political pressure or interference can result from the CNSC
fulfilling its mandate if it leads to a high-profile shortage of a
product, such as radio-isotopes from AECL's NRU reactor or
potentially electricity from OPG's reactors. As seen by the OPA's
proposal to operate reactors as long as possible to maintain
electricity supply, Ontario's looming electricity shortage will put
nuclear safety in conflict with maintaining electricity supply.
The unplanned shutdown of any of Ontario's nuclear stations over
the next decade could lead to the electricity shortages or an
inability for the Ontario government to phase out coal, undermining
action on climate change - both would be high profile issues of
public concern. Greenpeace believes that the CNSC should enact
policies now to pre-empt political pressures on the tribunal.
As noted, Greenpeace recommends that the Commission establish
and make public clear cut criteria for determining the end-of-life
for nuclear stations in Canada. Such transparent criteria,
Greenpeace feels, will aide in mitigating the potential for
political pressures to influence nuclear regulation.
Moreover, Greenpeace believes that the CNSC should review and
publish reviews of OPG's estimates of the fitness-for-service of
life-limiting components. Such independent and public assessments
would provide much needed scrutiny the OPA's and OPG's claims
regarding reactor service life, which are being used as the basis
for regarding Ontario's long-term electricity plan.
Recommendation: Given the current lack of end-of-life
criteria and the political pressures to maintain electricity supply
post 2010, Greenpeace Canada requests that the Commission require
OPG (as well as other licencees) and CNSC staff to submit and
report annually on the fitness-for-service assessments and
forecasts for the life-limiting components for nuclear stations in
Canada in its annual report on the performance of the Canadian
nuclear power industry. The Commission should also require OPG to
make available on request - outside of Access to Information - any
studies regarding fitness-for-service.
4. Pickering B Reactor Risks-High and Rising
The proposed licence period until 2013 would, if approved, bring
the Pickering B nuclear station to the end of its operational
life.
As noted, OPG's end-of-life estimates for the Pickering B
nuclear station changed significantly in 2006, moving from 2009 to
2014. OPG claims in its licence renewal submission that it could
operate the station until 2018. As discussed, Greenpeace believes
OPG has placed Ontario's electricity supply needs above safety
considerations in establishing these dates.
Greenpeace believes that the Commission must acknowledge that
the proposed licence period to 2013 is most likely Pickering B's
last operational licence. This period is arguably when the
Pickering B reactors will pose the greatest hazard to the
environment and Toronto.
Engineers use a concept called the "bath-tub curve" to assess
the impacts of ageing on facilities. The bath-tub curve plots the
hypothetical failure rates of components of an engineered system,
such as a nuclear reactor, over its life-time. The bath-tub curve
has three stages, each with a different hazard profile: the
break-in phase, the middle-life phase, and the wear-out,
end-of-life phase.
The two highest-risk phases are the break-in phase and the
wear-out, end-of-life phase. During the break-in phase, for
example, a reactor will have a higher risk of accidents as
construction and design flaws manifest themselves. Several
well-known international nuclear accidents occurred during or
shortly after the start-up of new reactors, notably the Fermi,
Three Mile Island, and Chernobyl accidents.
In Canada, a significant unforeseen accident occurred at the
Pickering A nuclear station in 1983 when a metre-long break
ruptured a pressure tube in Pickering Reactor 2, spilling 17 kg of
heavy water per second onto the floor of the reactor vault. The
leak rate was gradually reduced as the coolant pressure dropped.
The leak was stopped two weeks later.
The Pickering B reactors are now entering the wear-out end phase
of the bath-tub curve. This phase is when materials and components
deteriorate after years of operation, leading to increased risk of
system failures and accidents.
Given the complexity of a nuclear plant, the impacts of ageing
are not well understood and often only become apparent after
component failures, such as tubes bursting.
The Canadian nuclear industry uses modeling to try to predict
the rates of thinning, cracking and sagging but has repeatedly been
faced with ageing impacts unforeseen in its modeling. In 2006, for
instance, Hydro Quebec reported to the CNSC the appearance of
cracking in the feeder pipes of its Gentilly-2 reactor that were
unforeseen in the models used by the industry to predict the ageing
of pressure tubes.
The unpredictability of the impacts of reactor ageing increases
the likelihood of a greater number of shut-downs and inspections
for shut-down and maintenance.
Indeed, even the OPA acknowledges the potential for the
Pickering B reactors not reaching their claimed end-of-operation
date in 2014 in its discussions regarding electricity system
adequacy between 2008 and 2014. The OPA states: "There is a risk
that Pickering B units may reach the end of their operating life
ahead of schedule. For risk analysis purposes it was assumed that
there is a 10% probability that each Pickering B unit will cease
operation one year before its schedule end-of-life date."
As noted, OPG changed the estimated end of life from 2009 to
2014 for Pickering B in early 2006. Greenpeace believes that OPG
was motivated to push back the end of life date for Pickering B due
to the planning schedule it needs to prepare for rebuilding a
nuclear station. OPG informed the OPA in 2005, for instance, that
extending the life of a CANDU reactor requires up to six years of
planning and approvals, making it impossible for OPG prepare in
time for a refurbishment of Pickering B in 2009.
Greenpeace, then, is not confident that the OPG's projected
end-of-life - and the proposed licence period recommended to the
Commission - for the Pickering B nuclear station is founded on a
safety analysis uninfluenced by the business requirements of OPG.
There is a possibility that some Pickering B reactors may reach the
end of their operational life before the end of the proposed
licence period.
Recommendation: Given the uncertainties associated with
the operational life of the Pickering B Nuclear Station, Greenpeace
Canada requests that the Commission approve a 2 year licence
renewal instead of a 5 year renewal.
5. Requirement for an End of Life Plan
As discussed, there is a strong possibility that OPG may decide
not to rebuild the Pickering B nuclear station and or that the four
reactors will be unable to operate until their claimed end-of-life
date in 2014. For planning purposes, OPG and CNSC staff should
begin to plan for the safe shutdown and mothballing of the
Pickering B reactors.
According to correspondence acquired by Greenpeace through
Access to Information, CNSC staff were preparing in 2005 to
introduce a licence condition requiring New Brunswick Power to
prepare an acceptable plan for the end of life of the nuclear
station if a decision was made not to proceed with the
refurbishment of the Point Lepreau Nuclear Station. New Brunswick
Power also committed to prepare such a plan.
Given the uncertainties associated with Pickering B's
operational lifespan, OPG and CNSC staff should plan for the safe
shutdown and mothballing of the Pickering B reactors.
Recommendation: Greenpeace Canada requests that the CNSC
include a licence condition requiring OPG to develop an 'end of
life' plan for the station by 2010.
6. No Public Safety Case: Uncertainties and Transparency
Greenpeace is concerned that component wear-out will compound
the risks associated with Pickering B's design flaws.
This concern is heightened by the fact that many of Pickering
B's safety studies are conducted by OPG, which has shown a pattern
of behaviour that minimizes the risks a hazards posed by the
station. These studies are also not readily available for public
review, undermining their credibility.
Greenpeace has requested that the Commission direct OPG to
release the Pickering B Probabilistic Risk Assessment (PBPRA). The
Commission has refused Greenpeace's request, citing security
concerns.
Probabilistic Risk Assessments (PRA) are foundational safety
documents that inform nuclear licensing in Canada and Greenpeace
believes that they should be proactively released for public
scrutiny. Withholding PRAs in totality prevents the public and
decision-makers from being fully informed about nuclear risks. It
also prevents any possibility of independent peer review, thereby
undermining the credibility of the studies.
Because the Commission has used security concerns to withhold
the PBPRA in its entirety, Greenpeace feels that the Commission has
failed to make an adequate safety case for the continued operation
of the Pickering B nuclear station.
In its submission regarding the environmental assessment
guidelines for the life-extension of Pickering B in January 2007,
Greenpeace Canada stated its concern that OPG had refused to
include external hazards (such as seismic events, aircraft crash,
explosion, extreme temperatures, etc.) in the PBRA. External
hazards contribute significantly to the probability of accidents at
nuclear stations and excluding such events contributes to an
underestimation of accident probabilities.
Greenpeace noted that the CNSC's regulatory guide on
probabilistic risk assessment (S-294) requires the inclusion of
external events, although it does allow for the use of an
alternative analysis approach if an agreement is made between CNSC
staff and the licencee. OPG, however, did not consult CNSC staff
when it decided to exclude external events from the PBPRA. Indeed,
OPG verbally informed CNSC staff that "they do not intend to carry
out these assessments as the PRA is already done."
OPG's decision to exclude external events from the PBPRA without
consulting CNSC staff, Greenpeace believes, points to an approach
to developing safety studies that aims to underestimate nuclear
safety issues instead of addressing and mitigating such risks. This
undermines the credibility of the safety studies used by the CNSC
to justify the ongoing operation of Pickering B.
Notably, CNSC staff rightfully instructed OPG to include an
additional accident scenario in the environmental assessment for
the life-extension of Pickering B, citing the fact that if external
events were included in the PBRA it would increase the frequency of
the accident scenario to or greater than one in a million years,
which is the bounding probability for inclusion in environmental
assessments. OPG's response to this directive was to "…to revise
PBRA to reassess specific event sequences to improve their
frequency of occurrence." OPG, however, was unable to lower the
frequency of the accident scenario to the satisfaction of CNSC
staff.
OPG's refusal to redo the PBPRA to include external events when
considered alongside its willingness to rewrite the PRPRA to lower
the frequency a specific accident scenario points to an approach to
nuclear safety that aims to purposely underestimate the probability
accident sequences that may draw public attention to the hazards of
the Pickering nuclear station.
It is notable that the accident scenario OPG attempted to have
excluded from the environmental assessment for the life-extension
of Pickering B involves radioactive releases. According to
Emergency Management Ontario (EMO) radiation levels from this
accident scenario could necessitate evacuating up to a 10 km around
Pickering B. Such an accident would arguably have a greater
economic impact on Toronto than SARS. There are currently 238,088
people within 10 km of the Pickering nuclear station, the costs of
evacuation and lost economic activity would be enormous. Indeed, a
recent federal government study estimated that the cost of the
damage from a relatively small "dirty bomb" spreading radioactivity
for four kilometres in downtown Toronto would be $23.5 billion.
The CNSC regulatory approach relies on safety studies produced
by OPG and other nuclear licencees. A danger of this approach is
that it depends on the expertise of companies with an economic
motivation to minimize the costs of operating nuclear stations and
to downplay the probability of accidents that would negatively
impact the social acceptability of nuclear facilities. Due to
claims of commercial confidentiality, this approach also provides
limited opportunity for public scrutiny or independent assessment
to verify safety OPG's safety studies, undermining their
credibility.
It is notable that during the most recent licence period OPG
failed to inform CNSC staff of important safety studies regarding
the safety margins of the Pickering nuclear station. In June 2007,
OPG announced the closure of Pickering A units 1 and 4 in order to
perform maintenance on a backup electrical connection between
Pickering A and Pickering B. OPG acknowledged after the shut-down
that it was aware of the deficient backup electrical connection in
2005, but was studying the issue.
CNSC staff told Commission tribunal members that OPG should have
informed them of the issue in 2005 but that they did not learn of
it until 2007. The Pickering A nuclear station, then, operated for
two years outside of accepted safety standards due to OPG's failure
to inform CNSC staff of plant deficiencies.
As discussed, Greenpeace feels that the inability for the public
to scrutinize or verify OPG's safety studies undermines the
credibility of the safety claims made by the Commission.
It is noteworthy that CNSC staff evaluations of the Pickering B
Probabilistic Risk Assessment , however, point to additional
problems with the study that may underestimate risk, including
"significant deficiencies in the methodology" as well as a lack of
a sensitivity and uncertainty analysis.
Given OPG's pattern of underestimating or minimizing nuclear
hazards in its safety studies and the inability of the public to
scrutinize or review these studies, Greenpeace feels that the
Commission has failed to make an adequate safety case for the
continued operation of the Pickering B nuclear station.
Recommendation: Greenpeace requests that the Commission
improve its disclosure protocols and require the proactive release
all safety studies, including probabilistic risk assessments,
deterministic safety studies, hazards analysis and S-99
reports.
6.1 Design Vulnerabilities: Positive Void Coefficient
Being a CANDU design, the Pickering nuclear station shares an
inherent design flaw with the Chernobyl RBMK reactor design - the
positive void coefficient.
An important contributor to the 1986 Chernobyl accident was the
presence of steam in the fuel channels, which affected the nuclear
reaction in the core. The increase in reactor temperature resulted
in an increased production of steam, which has a lower density than
water. This created steam "voids" with no water coolant.
The Positive Void Effect, in particular its behaviour during
Large Loss of Coolant Accidents (LLOCAs), has long been categorized
as a Generic Action Item (GAI) by the Canadian Nuclear Safety
Commission and its predecessor the Atomic Energy Control Board
(AECB). GAIs are fundamental safety problems associated with CANDU
reactor technology
Since Chernobyl, international standards have developed to
favour more inherently safe reactor designs - that is, designs not
dependent on engineered safety systems or operational procedures
for the control of risk to prevent accidents - to the detriment of
reactors with positive void reactivity, specifically the Chernobyl
RBMK and CANDU designs.
In 2005, the CNSC released a draft design guide to the nuclear
industry for comment without informing non-industry stakeholders.
The draft design guide sought to be technology neutral and based on
international standards. In line with the direction of
international standards, the CNSC's 2005 draft design guide stated
that "…priority shall be given to nuclear reactor's inherent
negative feedbacks that shall mitigate any rapid increase in
reactivity and reactor power."
Greenpeace has requested the Commission's dispositioning of the
nuclear industry's comments on the 2005 draft design guide, but has
been denied by CNSC staff. Greenpeace has learned, however, that
Atomic Energy of Canada Limited (AECL) opposed the negative
reactivity requirement proposed in the 2005 design guide after
acquiring an internal CNSC memorandum that was mistakenly posted to
the CNSC website.
The memo notes that AECL opposed the requirement regarding
negative reactivity due to the negative impact it would have on
selling the CANDU design internationally and domestically.
Specifically, AECL complained to the CNSC staff that "…the clause
would impact on marketing of CANDU 6 reactors" and reflect badly on
operating CANDUs because "…every current reactor design has some
inherent characteristics that may increase reactivity in certain
design-basis events."
CNSC staff responded to AECL's concerns without broader public
consultation. Staff noted "…the need to address the immediate
urgent priority of providing regulatory guidance, especially for
new builds, imposes adopting an interim option using existing
approved regulatory documents and framework."
CNSC staff recommended removing wording requiring reactor
designs to "…attain at least a net negative effect of reactivity…"
with wording designed to accommodate reactors with positive
reactivity in draft regulatory guide S-337. Specifically, staff
recommended that the wording be changed to: "…it shall be
demonstrated that the consequences of those accidents that would be
aggravated by a positive reactivity feedback are either acceptable
or could be satisfactorily mitigated by other design features."
Greenpeace is disturbed that the CNSC has allowed the business
interests of AECL without public scrutiny to water down design
guidelines seeking more inherently safe reactor designs.
Recommendation: Given the undue and untransparent input
AECL has had in influencing CNSC standards to accommodate a
fundamental design flaws of CANDU reactors, Greenpeace requests
that the CNSC proactively release all internal documents and
correspondence from the "positive reactivity feedback working team"
which has been developing the CNSC's approach to dealing with the
positive void coefficient.
The international trend toward more inherently safe reactor
designs and away from designs with positive reactivity, such as the
CANDU and Chernobyl RBMK designs, calls for precaution in
relicensing the ageing Pickering B nuclear station.
Indeed, recent analysis regarding the extent of positive void
reactivity of the Pickering B reactors raises questions of whether
the safe operation the station can be assured under the current
licensing basis, especially given that Pickering B would not comply
with modern standards requiring negative reactivity.
The positive void effect has been long-standing and significant
because of the large power pulse it creates following a Large Loss
of Coolant Accidents (LLOCA).
Due to doubts that computer codes used to predict reactor
behaviour were not accurately estimating the impacts positive void
reactivity, CNSC staff requested in 2001 that all licencees confirm
that their safety analysis still conformed to the licensing
basis.
Because of the large safety margins predicted in earlier
analysis, Pickering B was the last station scheduled for a
re-assessment of a Large Break Loss of Coolant Accidents (LBLOCA)
with updated computer codes.
It is of great concern to Greenpeace that "…the new analysis has
resulted in prediction of consequences which are substantially
worse than reported previously." CNSC staff state that "…the new
analysis indicates a significant change in the licensing case
results and large reduction of previously reported safety
margins…". Furthermore, the results "…potentially invalidate large
parts of the licensing analysis documented in the Safety Report, in
particular, the moderator subcooling calculations, containment
analysis and assessment of radioactive releases and population
doses." According to staff, "…recent findings related to magnitude
of coolant void reactivity (CVR) and the other key parameters of
reactor core nuclear design further emphasize the need for a
comprehensive revisit of the safety case supporting the shutdown
systems effectiveness for AOOs [Anticipated Operational
Occurrences] and DBAs [Design Basis Accidents]."
Recommendation: Given recent findings regarding the
magnitude and impact of positive void reactivity on the safety case
for Pickering B, CNSC staff should make recommendations regarding
what precautionary operational measures, such as de-rating the
station, should be taken to mitigate the uncertainties in Pickering
B's safety margins.
6.2 Design Vulnerabilities: Containment
The Pickering nuclear station has a significant design flaw in
that eight reactors share both the containment and Emergency
Coolant Injection System (ECIS).
Containment at the Pickering Nuclear Station consists of eight
individual reactor buildings connected to one vacuum building by a
pressure relief duct. In the event of a serious accident, the
vacuum building is designed to suck up radioactive material and
steam, and to douse the steam with water in order to reduce
pressure on the containment system. This containment system is
designed to handle 530 gigajoules (GJ) of thermal energy (stored
energy and radioactive decay heat) from one reactor during a
one-hour period after shutdown. Thus, the containment system can
only deal with one accident at one reactor. This station design was
clearly motivated by a desire to reduce construction costs by not
building individual systems for each reactor. The designers ignored
the possibility of simultaneous accidents at two or more reactors.
Such accidents (known as common mode failures) can be caused by
external events such as earthquakes, weather-related problems,
electricity failures, or acts of malice due to war, terrorism or
sabotage.
Similarly, the ECIS at Pickering is a shared system. Pickering
"A" did not originally have an ECIS, and the system was built
during construction of Pickering "B". It was designed to provide a
flow rate of 640 litres per second (l/s), in order to deal with the
largest assumed leak at one reactor. Thus, the system can only deal
with one accident at one reactor. Like the containment system, ECIS
cannot deal with common mode failures resulting in major loss of
coolant accidents (LOCAs).
In its review of the OPG's Probabilistic Risk Assessment, CNSC
staff note the following significant omission:
"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
results, additional risk from adjacent units may not be negligible.
Furthermore, if multiple mitigating systems fail 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. We think these scenarios
should be considered."
As noted, the Pickering nuclear station is highly vulnerable to
terrorist attack because 8 reactors rely on the same containment
structures. Greenpeace is deeply concerned that OPG has only
assessed the impacts of a small aircraft strike in its safety
studies, but not that of an "…international large commercial
aircraft crash or other similar malevolent actions…"
Recommendation: Greenpeace requests that OPG and CNSC
staff be required to assess and report on the impacts of an
international large commercial aircraft crash at the Pickering at a
public meeting of the CNSC
7. Conclusion
Because of the high population density, regulatory authorities
would not allow a new plant to be built at Pickering today.
Given Pickering's location, design flaws and its ageing,
Greenpeace believes that the CNSC should exercise the utmost
precaution in determining the duration and level of scrutiny for
what could be Pickering B's final licence renewal.
Thank you for this opportunity to comment on the licence renewal
of the Pickering nuclear station.
If you have any questions or require any clarifications, please
don't hesitate to contact me.
Shawn-Patrick Stensil
Energy Campaigner
Greenpeace