NEA News 2005 - No. 23.1 - Nuclear Energy Agency
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Cov-NEA News 23 1 1/07/05 14:56 Page 1
NEA News 2005 – No. 23.1
In this issue:
Nuclear regulatory decision
making
An analysis of uranium
exploration and price
Lessons drawn from recent NPP
operating experience
Management of uncertainty in
safety cases and the role of risk
Safety of the nuclear fuel cycle
News briefs
N U C L E A R • E N E R G Y • A G E N C Y
NEA News 2005
No. 23.1
NEA News is published twice yearly in
English and French by the OECD Nuclear
Energy Agency. The opinions expressed
herein are those of the contributors
alone and do not necessarily reflect
Contents
the views of the Organisation or of
its member countries. The material in
NEA News may be freely used provided
the source is acknowledged.
All correspondence should be
addressed to: Facts and opinions
The Editor, NEA News
OECD Nuclear Energy Agency
12, boulevard des Îles
92130 Issy-les-Moulineaux Nuclear regulatory decision making 4
France
Tel.: +33 (0) 1 45 24 10 10
Fax: +33 (0)1 45 24 11 10 An analysis of uranium exploration
The OECD Nuclear Energy Agency and price 8
(NEA) is an intergovernmental orga-
nisation established in 1958. Its pri-
mary objective is to assist its member
countries in maintaining and further
developing, through international co- NEA updates
operation, the scientific, technological
and legal bases required for a safe,
environmentally friendly and econom- Lessons drawn from recent NPP operating
ical use of nuclear energy for peaceful
purposes. It is a non-partisan, unbi- experience 10
ased source of information, data and
analyses, drawing on one of the best
international networks of technical Management of uncertainty in safety cases
experts. The NEA has 28 member coun-
tries: Australia, Austria, Belgium,
Canada, the Czech Republic, Denmark,
and the role of risk 14
Finland, France, Germany, Greece,
Hungary, Iceland, Ireland, Italy, Japan,
Korea, Luxembourg, Mexico, the
Safety of the nuclear fuel cycle 18
Netherlands, Norway, Portugal, the
Slovak Republic, Spain, Sweden,
Switzerland, Turkey, the United
Kingdom and the United States.
The European Commission takes part
in the work of the NEA. A co-operation
News briefs
agreement is in force with the Interna-
tional Atomic Energy Agency.
For more information about the NEA,
The Generation IV International Forum
see:
www.nea.fr
enters a new phase 20
Editorial board:
Gail H. Marcus
Karen Daifuku
Nuclear power for the 21st century 21
Cynthia Gannon-Picot
Production/photo research:
Solange Quarmeau
Projected costs of generating electricity 24
Annette Meunier
Design/layout/graphics:
Annette Meunier Third phase of the TDB Project 26
Andrée Pham Van
Cover page: Yellow cake being filtered
New publications 27
(P. Lesage, AREVA, France), refined yellow
cake (NEI, United States), fuel rods at the
Eole experimental reactor (P. Stroppa, CEA,
France), pipe failure at Mihama Unit 3
(JNES, Japan), site characterisation for
geological disposal (Posiva Oy, Finland).
Ministers take a close look
at nuclear energy
Nuclear energy was the focus of considerable attention in this spring’s international
agenda. At the international conference on Nuclear Power for the 21st Century held
in Paris in March, 74 countries and 10 international organisations were represented.
In May, nuclear energy was also debated at the Meeting of the International Energy
Agency (IEA) Governing Board at Ministerial Level, the OECD Forum on Fuelling the
Future: Security, Stability, Development, and at the Meeting of the OECD Council at
Ministerial Level, held back-to-back with the OECD Forum.
At the Nuclear Power for the 21 st Century conference, opinions about nuclear
energy were largely, though not exclusively, positive. Many Delegates tended to consider
that nuclear energy can, under the right conditions, be part of a response to the
challenge of meeting expanding energy demand, ensuring the security of energy supply,
while addressing climate change. An overview of the main themes covered during the
conference is provided in the news brief on page 21.
In the other meetings, the focus was less on nuclear energy and more on energy issues
all-around. At the OECD Forum, the general sentiment was that urgent action was
required in the energy sectors of both developed and developing countries. Ministers
at the Meeting of the IEA Governing Board at Ministerial Level stressed that energy
security remained their core mission, and described their vision of energy security as
greater global availability of reliable, affordable, clean energy. At the Meeting of the
OECD Council at Ministerial Level, on 3-4 May, Ministers underlined that sufficient
supply of clean and affordable energy is crucial for economic and social development.
They further considered that investment in energy technology and infrastructure must
2 Editorial, NEA News 2005 – No. 23.1
be directed towards sustainable, efficient technology with less negative climate impact.
During a joint meeting held between the Delegates attending the Meeting of the OECD
Council at Ministerial Level (MCM) and the Meeting of the IEA Governing Board at
Ministerial Level, participants discussed how governments can improve the framework
conditions to ensure timely investment in energy infrastructure that meets the tests
of security of supply, economic efficiency, environmental sensitivity and affordability.
The messages from these high-level gatherings seem clear, and I firmly believe that
we cannot afford to underestimate the importance of meeting the energy challenges
before us. Our economies depend upon it, as do our health and well-being. Meeting
growing energy demands must be done with due consideration for preserving the
environment. To succeed, a full range of approaches – starting with energy conservation
measures, but also including cleaner energy sources, greater use of renewables and
appropriate environmental-preservation agreements and incentives – will be necessary.
Luis E. Echávarri
NEA Director-General
Editorial, NEA News 2005 – No. 23.1 3
Nuclear regulatory
decision making
B. Kaufer, T. Murley *
Nuclear safety regulators are continuously faced with making regulator’s decision-making
a wide variety of decisions. Some of these may be made on process. In light of these
insights, the NEA Committee on
the regulator’s own initiative, for example a regulation on
Nuclear Regulatory Activities
new reporting requirements, but the large majority of (CNRA) judged that it was an
decisions are made in response to stimuli from outside the appropriate time to examine
organisation. A new CNRA report 1 has found that in all the broad issue of regulatory
decision-making scenarios, whether difficult or straight- decision making. That judge-
forward, the nuclear regulator will benefit from a structured ment was the basis for deciding
to prepare a report providing
decision-making framework. an international consensus on
the integrated decision-making
process. To pursue this objec-
tive, an expert group was
formed with senior-level regu-
N uclear power programmes
in OECD countries have
matured over their four
and insights from operating
experience, especially from the
accidents at Three Mile Island
lators.
decades of commercial oper- and Chernobyl; in the consid-
ation; this maturation has eration of human factor and
brought many improvements in organisational impacts upon
safety through backfits in tech- nuclear safety; and in an
nology as well as programmes increased emphasis on quality
and improvements in opera- management systems.
tional performance of nuclear It has been recognised for
power plants generally. In par- some years that the nature of
allel with these changes in the relationship between the
nuclear plants’ performance, regulatory body and the oper-
safety regulation of nuclear ator can influence the opera-
power plants has matured, tor’s safety culture at a plant,
most notably in the use of new either positively or nega-
safety analysis methods such as tively.2,3 An important factor
probabilistic safety analysis affecting the relationship
(PSA); in the regulatory between the regulator and the
responses to new information operator is the nature of the Types of regulatory
decisions
Perhaps the bulk of the deci-
sion cases that come before a
regulator are straightforward
* Mr. Barry Kaufer (email: barry.kaufer@oecd.org) works in the NEA Nuclear issues, but that does not mean
Safety Division. Dr. Thomas E. Murley (email: temurley@erols.com) is a former
Director of the Office of Nuclear Reactor Regulation at the United States Nuclear that they are unimportant or
Regulatory Commission and is a consultant to the NEA. that the regulator does not
4 Facts and opinions, NEA News 2005 – No. 23.1
need to consider them care- fundamental distinction in ments to satisfy the opera-
fully. Rather, it simply means roles between the operator tional needs of the plant
that there are substantial prece- and regulator. A regulator’s operator?
dents of case histories and ade- decisions must be grounded in This questioning is not
quate time for the regulator to the nation’s laws and the regu- meant to suggest that the reg-
define the issues clearly, to lations and standards that ulator should allow itself to
analyse alternative actions and implement those laws. But become paralysed by concerns
to involve the appropriate even further, the regulatory that a decision may not turn
stakeholders. In other words, body should promote safety by out well. Rather, it is a
for such issues there is ample setting a good example in its reminder that the regulatory
opportunity for the regulator own performance. body should assure itself that
to implement its deliberative, When approaching regula- it has approached the decision
structured decision-making tory decisions several basic following its procedures in a
process. principles can be applied such structured manner, has consid-
Some of these decision as assessing safety significance, ered all relevant input, has
issues will be more challenging gathering sufficient information used sound safety principles
for the regulator. They are fre- to make an informed decision, and has not appeared to be
quently characterised by unex- seeking input from outside unduly pressured in making
pected circumstances, lack of stakeholders, maintaining con- the decision.
complete information, uncer- sistency in decisions, and most
tain or contradictory informa- importantly, acting as a com- Criteria for regulatory
tion, disagreement among the petent, professional, independ- decisions
safety experts, a real or per- ent body that makes regulatory
ceived urgency to make a decisions on the basis of pro- Current, comprehensive and
decision, an incomplete under- tecting safety, security and the clear regulations are essential
standing of the consequences environment. for a good decision-making
of a decision, or all of the process, but these cannot cover
In making a decision on a
above. Adding to these difficul- all the aspects of the issues that
difficult issue, the regulator
ties is often the concern in the a regulator will face. There will
will have to consider how the
mind of the regulator that its always be questions of com-
decision will appear in retro-
decision-making actions may pleteness, differing interpre-
spect if it turns out to be
have profound effects not only tations and unexpected situ-
wrong or not to have the
on public safety but on the ations. For these reasons a reg-
desired outcome. In difficult
public’s perception and confi- ulatory body will usually be
cases there will frequently be
dence in the regulatory body guided by broad criteria that
pressure on the regulator from
itself. form the foundation of its
many sources, so the regula-
Whether a decision issue is safety philosophy.
tory body should ask itself
straightforward or difficult, a some questions before render- One of these criteria is the
nuclear regulator will benefit ing a final decision: level of safety and environmen-
by having a structured decision- tal protection to be required by
● Is there a clear safety basis
making framework and by the regulator. There are vari-
for the decision?
having experience in follow- ous statements on the basic
● Is there a clear legal basis level of protection criterion in
ing its procedures.
for the decision? OECD countries, but they all
● Were normal procedures fol- acknowledge that it is not pos-
Basic principles for
lowed? sible to achieve zero risk in
regulatory decision making
● Were all stakeholder views nuclear activities. Some of the
A fundamental tenet of considered? criteria for the basic level of
nuclear safety is that the oper- protection in OECD countries
● Was there due diligence
ator has the responsibility for are:
used in gathering the neces-
safely operating its nuclear ● no unreasonable risk,
sary information?
power plant(s). It is the
● Is the decision consistent ● adequate protection of pub-
nuclear regulator’s responsi-
with earlier precedents? lic health and safety,
bility to oversee the operator’s
activities in order to ensure ● Has the regulator ensured ● risk as low as reasonably
that the plant is operated that the decision was not practicable,
safely. Nothing the regulator made prematurely, bypass- ● safety as high as reasonably
does should ever diminish that ing some regulatory require- achievable,
Nuclear regulatory decision making, NEA News 2005 – No. 23.1 5
C. Cieutat, La Médiathèque EDF, France
Miklos Beregnyei, PAKS NPP, Hungary
AECL, Canada
Some of the criteria for the basic level of protection in OECD countries include adequate protection of public
health and safety, risk as low as reasonably practicable, and safety as high as reasonably achievable.
● risk limited by use of best the health and safety of people earliest days of commercial
technologies at acceptable living near nuclear power nuclear power, regulators have
economic costs. plants. In order to be more embraced defence in depth to
A related question is what useful in practical decision require multiple layers of pro-
criterion should be used for making, the health goals are tection to prevent accidents
the level of assurance that the often supplemented by numer- and to mitigate their conse-
required safety criteria are met? ical goals for core damage fre- quences. The use of defence-
Here again, there are various quency (CDF) and large, early in-depth principles and safety
formulations of the criterion radioactive release frequency margins have been, and con-
(LERF). Clearly the use of tinue to be, effective ways to
for the level of assurance in
these latter safety goals account for uncertainties in
OECD countries, but they all
requires the production and equipment and human per-
recognise that absolute assur-
maintenance of high-quality, formance. As more operating
ance cannot be achieved. Most
plant-specific PSAs as well as experience and improved
countries have some variation
operator and regulatory staffs safety analysis methods give
of a “reasonable assurance”
proficient in PSA methodology. us a deeper understanding of
criterion.
Although the promulgation nuclear plant safety, safety
These criteria are seen to be and use of quantitative safety margins and their uncertain-
qualitative aspirational criteria goals is fairly common among ties, it may be possible to
rather than quantitative safety OECD regulatory bodies, these reduce overly conservative
requirements that must be met. criteria are generally regarded margins or to add margins
In practice, they are what as not appropriate for use as where needed.
some may call “revealed stan- the sole basis for making regu-
dards”. That is, the sum of per- latory decisions. Instead, the
haps hundreds of case history quantitative safety goals are
Elements of the regulatory
decisions and case law over best used as guidelines by the decision-making process
several years will yield a work- regulator to supplement other The basic principles and cri-
ing definition of what these regulatory criteria. teria for regulatory decision
criteria mean. A fundamental principle for making should be embodied in
Beyond these qualitative safety regulators is the practice a practical, integrated frame-
aspirational criteria a regula- of conservative decision mak- work that regulators can use in
tory body may adopt quantita- ing. This is exemplified by the their daily activities. The frame-
tive safety goals – for example, traditional defence-in-depth work need not be rigid but
numerical goals for protecting safety philosophy. Since the must be consistent with national
6 Facts and opinions, NEA News 2005 – No. 23.1laws, customs, international system, similar to its planning Conclusion
treaties, regulations and the and budgeting processes, tak-
There is no guide or hand-
internal policies of the regula- ing into account the national
book that will tell a regulator
tor. The basic elements of an laws, customs and internal
how to make a proper deci-
integrated framework are to policies of the regulator. In
sion, especially for difficult
(a) clearly define the issue, this way the decision-making
cases where the issues may be
(b) assess the safety signifi- process will over time become
contentious and the circum-
cance, (c) determine the laws, part of the culture of the regu-
stances unique. That is the
regulations or criteria to be latory body’s organisation.
value of having a decision-
applied, (d) collect the rele- The integrated decision- making framework to fall back
vant information and data, making framework will cover on. Beyond that, the regulator
(e) judge the expertise and the the great majority of decisions will have to rely on its experi-
resources needed, (f) agree on faced by a regulatory body. ence and good judgment, keep-
the analyses to be performed, But every regulator will ing in mind that safety, and, to
(g) assign priority to the issue encounter special situations some degree at least, the credi-
among the other tasks of the that are unique in some aspect bility of the regulatory body
agency, (h) make a well- or that do not fit neatly into may be at stake in the regula-
informed decision, and finally the framework outlined above. tory decision and the way it is
(i) write a clear decision and The CNRA report on Nuclear made. ■
its basis, and publish the deci- Regulatory Decision Making
sion when needed. provides advice on how best
The elements above are to approach a number of these
not meant to be followed in types of situations, notably:
sequential order; in fact, sev- decision making in the face of
eral of them can be conducted uncertainties, handling safety
in parallel and some could culture issues, facing differing
even be omitted in certain sit- opinions, considering informa-
uations. The rigour and depth tion from safety advisory bod-
with which the elements are ies and using risk information
followed should generally be in regulatory decisions.
proportionate to the safety and
regulatory significance of the Communicating regulatory
issue being considered.
decisions
The regulator’s responsi-
bility does not end with the In any discussion of the
decision and its publication. basic principles and criteria
Clearly, there are follow-up that a safety regulatory body
actions a regulator should take should consider when making
to ensure that its decision is a decision that can affect a
implemented. Likewise, the wide range of stakeholders, it
decision and its basis must be is necessary to keep in mind
stored in the regulatory body’s how those stakeholders might
established document control view the decision and its
system. This will enable effec- rationale. In this regard, it is
tive follow-up actions and will important for the regulatory
facilitate retrieval of the infor- body to consider how its deci-
sions are communicated to its Notes
mation to assist in future deci-
sion making. stakeholders. 1. The CNRA booklet on Nuclear
For many of the difficult Regulatory Decision Making was
published this spring and is available
Implementing the elements issues facing the regulator, the on the NEA website at www.nea.fr
outside party most directly and upon request from the NEA
of the decision-making Secretariat. Its contents formed the
affected will be the plant oper-
process basis for this article.
ator. In some complex or con-
The regulatory body can use tentious cases, the regulator 2. NEA (1999), The Role of the Nuclear
Regulator in Promoting and Evaluat-
the elements above to develop may want to explain the writ- ing Safety Culture, OECD/NEA, Paris.
a regulatory decision-making ten decision in a meeting with
3. NEA (2000), Regulatory Response
framework and to integrate it the operator, perhaps in a Strategies for Safety Culture Prob-
into its overall management meeting open to the public. lems, OECD/NEA, Paris.
Nuclear regulatory decision making, NEA News 2005 – No. 23.1 7An analysis of uranium
exploration and price
R. Price *
The primary production of uranium has been less than reactor Yet, despite the significance
requirements since the mid-1980s and secondary sources of this increase in relative terms,
have had to make up the difference. By 2002, world uranium this price rise remains relatively
modest at this point when com-
production provided only about 54% of world reactor pared with the historic peaks
requirements. This dependence on secondary supplies is of the 1970s or even the short-
projected to continue into the near future. Over the longer lived peak in the mid-1990s,
term, however, primary production will need to expand. especially when viewed in
constant terms (see Figure 1).
Will this increase in market
O ne result of the abundance
of secondary sources has
been a consistently depressed
price of uranium. Since the
beginning of 2001, the price
of uranium has rebounded
price result in the increased
exploration needed to support
new production capability? To
market price for uranium over from lows not seen since the answer this question, a review
the past several decades. These early-1970s, and had almost of the data collected over the
low market prices led to the doubled by July 2004.1 past 40 years was conducted to
curtailment of exploration and
the closing and/or consolida-
tion of many uranium produc-
tion companies and production
centres. Consequently, during Figure 1. World exploration and uranium price, in 2003 US dollars
this time the level of uranium (1970-2002)
exploration has been at low
levels and mainly oriented 2003 USD Uranium price World exploration 2003 USD
towards development. 1.4x109
100
Yet, after 2020, when sec-
ondary sources of uranium 1.2x109
are expected to decline in avail- 80
ability, reactor requirements will 1x109
have to be increasingly met by
60 8x108
primary production. To meet
this increasing demand, pri-
mary production capability will 6x108
40
need to increase significantly.
As a first step, new exploration 4x108
will be needed to provide the 20
increased resource base neces- 2x108
sary to support this expansion.
A barrier to new exploration 0 0
has been the low price for 1970 1975 1980 1985 1990 1995 2000
uranium. Year
Over the past several years,
though, there has been a sig- * Mr. Robert Rush Price (e-mail: robert-rush.price@oecd.org) works in the NEA
nificant increase in the market Nuclear Development Division.
8 Facts and opinions, NEA News 2005 – No. 23.1attempt to determine whether Figure 2. World exploration expenditures versus uranium price
exploration could be expected (2003 USD, 1970-2002)
to respond to this price recov- 2003 USD Exploration expenditures
ery, and in what time frame
1.6x109
increased exploration could be World exploration with 1-year lag v U price (1970-2002)
expected to result.
1.4x109 A = -6.13745 x 107 t = -1.177267
Data on uranium exploration
B = 1.437 x 107 t = 15.96424
was taken from the OECD/ R = 0.94588
1.2x109
NEA series of publications
entitled Uranium Resources,
Production and Demand 1x109
(known as the Red Book). The
data there represent the total 8x108
amount of money spent on
exploration within a given 6x108
country regardless of whether
the source was domestic or 4x108
foreign. Data on the price of
uranium was taken from 2x108
NUEXCO/TradeTech and was
the annual average of the end- 0
of-month unrestricted
exchange values (without pre- 0 20 40 60 80 100
miums).2 Uranium price, 2003 USD/lb U3O8
A look at Figure 1 indicates a
possible correlation between indeed following as predicted, vide the resource base
price and exploration and but press reports are providing required to build new or
further points to a time lag circumstantial, anecdotal evi- expand existing production
between a change in uranium dence that exploration activity capability. An analysis of his-
price and changes in explora- is already picking up in torical information indicates
tion expenditures. For world Australia, Canada and the that past price increases have
expenditures, the best correla- United States, thus leading to resulted in increased explo-
tion was observed with a one- the conclusion that data will ration. Recent price increases
year delay (see Figure 2). likely show an increasing can therefore be expected to
The improvement in correla- trend. begin the increased exploration
tion when a time delay is Analysis using surface drill- needed to support the expan-
introduced corresponds logi- ing data, a more direct meas- sion of uranium production
cally to the delays as the influ- ure of exploration activity, was capability. ■
ence of the uranium price also conducted to see if this
change works its way through would lead to a better predic-
the decision-making process in Notes
tor. Adequate data on surface
the exploration companies, as drilling was available for 1. TradeTec, LLC (from www.uranium.
well as the time needed to ini- info/index.html).
Australia, Canada and the
tiate field studies once a deci- 2. Total exploration expenditure
United States for the period includes exploration and devel-
sion has been reached. The 1975-2002. When plotted, how- opment expenditures. Exploration
results suggest that exploration ever, the results were similar includes the costs of all types of
is a competitive and open sec- surveys, including: surface and
and showed no improvements underground drilling, logging, test
tor of the uranium industry, over the results provided in mining and other costs related to the
sensitive to uranium price, and Figure 2. search for new deposits or exten-
sions to known deposits. Prior to
aggressively responds to mar- With reactor requirements to 1989 world data does not include
ket signals. be increasingly met by primary the countries associated with the
former Soviet Union and certain
The results indicate that production in the coming other non-western countries, e.g.
even relatively modest price years, it is necessary to ensure China and Mongolia, and so
increases are followed by that sufficient new discoveries represents only a sample of world
activity and not the entire popu-
increases in exploration of uranium are made to enable lation. The inflation index used to
expenditures. Data for 2004 the expansion of production convert to constant 2003 dollars was
exploration expenditures is capability as secondary sources the Producer Price Index. Historical
values of this index were obtained
not yet available to verify decline. Increased exploration from http://www.jsc.nasa.gov/bu2/
whether market behaviour is activity will be needed to pro- inflation/ppi/inflatePPI.html.
An analysis of uranium exploration and price, NEA News 2005 – No. 23.1 9Lessons drawn from recent
NPP operating experience
P. Pyy *
C ountries need timely feed-
back from international
nuclear power plant (NPP)
WGOE
All three of these areas illus-
trate the continuing need to
institute an appropriate and
operating experience in order The NEA Working Group on timely corrective action pro-
to manage the safety of their Operating Experience (WGOE) gramme both by the utilities
installations effectively. One has an important task to and the regulators in order to
way to obtain this type of refine and report messages avoid recurrence.
from international nuclear
information is through the
power plant operating experi-
annual technical notes about Electrical disturbances
ence to NEA member coun-
lessons drawn from recent
tries. This is done via Several electrical events,
nuclear power plant operat- reporting to the NEA Com-
ing experience prepared by both plant-centered and in
mittee on the Safety of
the NEA Working Group on the off-site grid, have been
Nuclear Installations (CSNI)
Operating Experience (WGOE). reported in recent interna-
and the NEA Committee on
This article is based on the Nuclear Regulatory Activities
tional operating experience.
technical note for events (CNRA). Apart from technical The previous technical note
experienced in 2003-4 1 (the notes, the WGOE issues [NEA/CSNI/R(2004)4] reported
third in the series 2). technical reports about the August 2003 massive grid
The WGOE technical notes selected topics dealing with disturbance in the United
are based on the issues the analysis of nuclear oper- States, which propagated into
reported in the joint NEA/ ating experience, including parts of Canada, and more
risk insights where relevant. information has recently been
IAEA Incident Reporting
The group also seeks to presented. For example, the
System (IRS) and, in some
advance practices to collect Pickering station, which con-
cases, the NEA joint safety and analyse operating experi-
projects dealing with operat- sists of eight units, experi-
ence in member countries.
ing experience data collection enced a total loss of off-site
and analysis. The safety issues power and natural circulation
identified in the technical notes secured the plant cooling for a
are generic in nature and, con- number of hours. The event
sequently, useful to decision revealed deficiencies in a num-
Recent safety issues
makers. However, it is also ber of safety systems, includ-
emerging from the Incident ing emergency service water,
suggested that national regula-
Reporting System firewater, standby diesel gener-
tory bodies, technical support
organisations and nuclear oper- Recent events of safety sig- ators, and the licensing basis
ators put them in national con- nificance reported to the IRS for these and other systems.
text to see if they are relevant include erosion-corrosion of Corrective actions, including
to the safety of the nuclear piping, electrical disturbances, changes in plant design and
power plants (NPPs) in their and foreign material intrusion operation, are currently being
countries. into the primary coolant system. taken.
Furthermore, in June 2004
there was a loss of off-site
power at the Palo Verde NPP
* Dr. Pekka Pyy (e-mail: pekka.pyy@oecd.org) works in the NEA Nuclear Safety in the United States involving
Division. a complete loss of 5 500 MWe
10 NEA updates, NEA News 2005 – No. 23.1cladding was likely caused by
IRS pieces of the gasket that went
through them.
The Incident Reporting System (IRS) is the only international
reporting system for regulators and governmental organi- Another foreign material
sations which provides an assessment of safety-significant intrusion event was experi-
nuclear power plant events, as well as detailed information enced at the Fessenheim facil-
on analyses of the root causes and lessons learnt from the ity in France. A human action
safety perspective. The IRS is operated by a joint IAEA and on a valve alignment in the
NEA secretariat. A guideline for IRS reporting has been in use chemical and volume control
since June 1998. The system, based on quarterly CD distri- system (CVCS), combined with
bution, is now in use in 31 countries. In 2005, it is planned
a design modification, resulted
to make trial use of the web-based IRS. Periodic reports on
Nuclear Power Plant Operating Experience (the “Blue Book”)
in intrusion of demineralised
have been published for the periods 1996-1999 and 1999- resins into the primary coolant
2002. The next Blue Book for 2002-2005 is planned for system. This led to the contam-
spring 2006, in conjunction with the International Conference ination and exposure of work-
on Future Uses of Operating Experience scheduled to take ers, obstruction of the sampling
place in Germany. system, and a six-month out-
age of the facility for cleanup
and repair. The nuclear safety
consequences included inop-
erability of a number of con-
trol rods, blockage of injection
to reactor coolant pump seals,
and increased potential for
of generating capacity on the Foreign material intrusion failure of high-pressure injec-
grid, including more than into the primary system tion pumps due to bearing
3 700 MWe from the three failure.
There have recently been
units at Palo Verde. The cause Although foreign material
two significant events involving
was traced to a single failure intrusion is a recurring con-
foreign material intrusion. At
of protective circuitry at an cern, these two events were
the Tihange plant in Belgium, a
off-site substation. In general, particularly significant. The
severely damaged spiral-wound
the station responded accord- first one led to a fuel failure
metallic gasket was found in a
ing to design, although one and the second one to safety
safety injection system check
emergency diesel generator system impairments and a
valve, and a fuel failure was
failed to start. It was observed long outage.
observed some months later.
that the transmission company
The fuel anti-debris devices
operators had not analysed a
were unable to catch some Erosion-corrosion of piping
situation involving the simulta-
portions of the gasket, and the As regards piping, a signifi-
neous loss of all three units. mechanical damage of the fuel
The event was considered risk- cant event occurred at the
significant and the corrective Mihama plant in Japan that
actions included improvements New and severely damaged involved the failure of a con-
in the off-site grid components. gaskets at the Tihange plant. densate water pipe in the tur-
bine hall. The event resulted
These loss of off-site power
in severe injuries to plant per-
events had common messages:
sonnel, including five fatali-
1) the operating utilities may
ties. Some of the main
have inadequately analysed
features of the event are:
grid disturbances; 2) there is a
need to review operating pro- ● The ruptured portion of the
cedures, communication plans, piping should have been
equipment and the licensing inspected according to plant
basis for a widespread and guidelines. However, it had
long loss of off-site power not been inspected since
event, and 3) there may be the plant start-up in 1976.
frailties in the interconnected ● An unauthorised residual
AVN, Belgium
grids when large concurrent life evaluation rule was
trips of generating capabilities applied by the plant oper-
occur. ating organisation.
Lessons drawn from recent NPP operating experience, NEA News 2005 – No. 23.1 11● The quality management removal in reduced inventory the fact that both the licensee
system of the operating conditions during outages. and the contractor organisa-
organisation was not suffi- More than 50 such events have tions may experience loss of
cient to check the con- occurred over the past 25 years. competence via outsourcing.
tracted work. Several types of regulatory cor- Small utilities and regulatory
● The secondary piping rective action approaches have bodies dealing with large and
inspection had been within been used, ranging from infor- sometimes multinational con-
the scope of the utility’s mation notices, advisories and tractor organisations seem to
self-imposed inspections. suggestions, to formal and be most vulnerable to this.
binding decisions by the regu- Member countries gave sev-
A number of precursor
events have taken place at latory authorities. In 1988, the eral presentations about events
similar plants, for example in US NRC issued a generic letter involving contracted work,
Japan and in the United States with non-binding suggestions including a brief interruption in
(e.g. at Surry in 1986), and on means for reducing the decay heat removal due to
many of them may be found number of occurrences. A maintenance during an outage,
in the IRS database. As a cor- notable effect was observed, a plant start-up before some
rective action, improvements but events continue to occur, scheduled contracted work
even in 2004. By contrast, for could be completed, and manu-
in inspection practices of both
instance, France and Korea facturing deficiencies in the
the operator and the regulator
issued binding requirements component cooling water sys-
are being considered and/or
that seem to have stopped the tem heat exchangers.
already applied. For instance,
since 1 October 2003 this pre- recurrence there. In France, an Ideas on how to avoid
viously self-imposed inspection automatic makeup function problems with contracted
is now legally required, and was provided; a detailed work work and to improve the situ-
the Japanese regulatory agency schedule and necessary condi- ation were presented. There
NISA (Nuclear and Industrial tions were required prior to was agreement that the licens-
Safety Agency) reviews second- mid-loop entry; and a vortex ees must be able to exercise
ary wall thickness inspection detection device was installed. contractor supervision in all
by the utilities. In addition, the In Korea, there were require- circumstances. However,
Japanese Society of Mechanical ments for better training of some events indicate a grow-
Engineers is preparing a pip- staff, better level instruments, ing problem of detecting sub-
ing thickness management revision of residual heat standard performance. In addi-
standard, and NISA has recently removal pump procedures, tion, the licensees need to
issued guidelines for the ins- review of critical level calcula- qualify the contractors, but the
pection and management of tions and revised technical procedures for this may not be
specifications. adequate or even exist in the
pipe and wall thinning.
The WGOE is currently inves- light of recent experience.
tigating whether a similar study Furthermore, matters such as
Recent safety issues training on nuclear-specific
on the risk-significant issue of
emerging from other WGOE loss of heat sink or loss of requirements must be
work service water to safety-related addressed by the licensee.
Other work carried out by equipment should be initiated. Contracting and subcontract-
the WGOE has highlighted ing may, if not handled ade-
additional safety issues includ- quately, lead to losing a long-
Events involving
ing recurring events, events term safety focus. Core compe-
contractors tencies must always be kept
involving the use of and per-
The theme chosen for the in-house in order to remain
formance of contractors, and
WGOE in-depth discussion at an intelligent customer. This
the origins of common-cause
its annual meeting in 2004 was includes, independently of
failures (CCFs).
the influence of contractor the domain, the ability to
(and subcontractor) work on qualify contractors, oversight
Recurring events the evolution of events. There of training of contracted per-
The WGOE has continued is an increasing use of contrac- sonnel, supervision and
to study recurring events (it tors and subcontractors in the approval of contracted work,
previously issued two reports nuclear industry, although out- and most importantly, continu-
on the topic). The latest theme sourcing is not new. Concerns ing involvement in the mainte-
concerns corrective actions about the use of contractors nance of safety-focused
against PWR loss of decay heat have increased lately due to thinking.
12 NEA updates, NEA News 2005 – No. 23.1well-known, but information
ICDE does not always seem to reach
end-users and/or corrective
The International Common-cause Data Exchange (ICDE) proj-
ect was initiated in August 1994. The countries participating action programmes are not
in the third agreement phase of ICDE are: Canada (CNSC), always rigorously imple-
Finland (STUK), France (IRSN), Germany (GRS), Japan mented. More needs to be
(NUPEC/JNES), Republic of Korea (KAERI), Spain (CSN), done internationally to share
Sweden (SKI), Switzerland (HSK), United Kingdom (NII) and experience on safety issues
the United States (NRC). The objective of the ICDE project is and their solutions, and to
to draw qualitative and quantitative insights from interna- make sure that the information
tional operating experience data to help avoid common-cause
reaches the end-users at the
failures or to mitigate their consequences. The ICDE data
include both those events reported to regulatory bodies and NPPs.
those based on additional analysis of proprietary nuclear The main findings that oper-
power plant databases. The main findings of the project are ation and maintenance domi-
reported publicly. nate as causes for common-
cause failures, and a number
of recent events dealing with
the increased role of contrac-
tors and subcontractors, show
that the utilities and regulators
Common-cause failures prevented with adequate prac- may need to enhance over-
of batteries tices and surveillance of the sight of the organisational
The International Common- circuit continuity. arrangements, competence and
cause Data Exchange (ICDE) Generally, the main areas safety culture of the licensees
project has exchanged infor- for improvement to prevent to ensure the safe operation
mation on common-cause fail- common-cause failures at NPPs and maintenance of NPPs.
ures (CCFs) for more than ten are, according to the project Finally, an operating experi-
years. The project’s most findings: 1) scrutinizing existing ence reporting and analysis pro-
recent report, issued in late operation, maintenance and gramme is a prerequisite to
2003, was about batteries.3 testing procedures for deficien- successful safety management
cies creating the potential for and is stipulated in the Conven-
Deficiencies in design were tion on Nuclear Safety. In addi-
CCF of redundant systems,
involved in about half of all the tion to this, many problem
2) ensuring comprehensive
events. Of those, more than areas also require a review of
work control, 3) comprehen-
90% occurred during battery sively prescribing the testing operating experience on lower
manufacture, e.g. inadequate steps required in the requalifi- levels than plant events and
selection of component materi- cation of components or sys- combining this review with
als for the plates, in the elec- tems after maintenance, repair other analyses – such as PSA,
trolyte, in separators, in cells, or backfitting work, and organisational and task analy-
or in terminal connections, and 4) intensifying training, intro- ses, materials analyses and
less than 10% occurred during ducing ergonomically better thermal hydraulic calculations
the plant specification or modi- designs and introducing more – to find permanent solutions.
fication process, e.g. calculation Such a cross-disciplinary
key locks. These findings
errors in the capacity definition. approach challenges the
apply to all component types
Deficiencies in maintenance nuclear safety community to
which have been analysed in
and testing were involved in progress to the new era of
the ICDE project.
less than half of the events. Of safety management. ■
these, approximately half were
due to physical failures in the Concluding remarks
battery subcomponents, nearly Almost all of the significant Notes
30% were due to electrical fail- events reported recently in
1. “Lessons Drawn From Recent Nuclear
ures, some 20% due to direct international meetings have Power Plant Operating Experience”,
human actions, and one event occurred earlier in one form NEA/CSNI/R(2005)4.
was due to premature ageing or another. Similarly, most of 2. The first two WGOE technical notes
caused by lack of mainte- the topics highlighted in the are referenced as NEA/CSNI/R(2002)
24 and NEA/CSNI/R(2004)4.
nance. The data suggests that 2001-2 and 2002-3 technical
3. “ICDE Project Report: Collection and
the majority of maintenance notes are still valid. Counter- Analysis of Common-cause Failures
and testing events could be actions are in many cases of Batteries”, NEA/CSNI/R(2003)19.
Lessons drawn from recent NPP operating experience, NEA News 2005 – No. 23.1 13Management of uncertainty
in safety cases and the role
of risk
B. Dverstorp, A. Van Luik, H. Umeki, S. Voinis, R. Wilmot *
D eep geological repositories
aim to protect humans and
the environment from the haz-
current level of technical
understanding established
through uncertainty analysis.
be described in the safety case
at each stage.
There is a clear consensus
ards associated with long-lived A safety case 1 is a key input among all national programmes
radioactive waste over time- to support the decision to on the importance of managing
scales often up to several thou- move to the next stage in uncertainties in a safety case.
sand or even a million years. repository development. A Managing uncertainties and
Radioactive waste management key output of the safety case establishing levels of confi-
thus involves a unique consid- is the identification of uncer- dence can be approached in
eration of the evolution of the tainties that have the potential different ways. This requires a
waste and engineered barriers, to undermine safety. The con- clear classification of the uncer-
and the interactions between nection therefore needs to be tainties since a large range of
these components and geologi- made between key uncertain- uncertainties are to be han-
cal barriers over very long ties that have been identified dled. Various classifications of
periods of time. Over long and the specific measures or uncertainty exist – such as
actions that will be taken to epistemic uncertainties, uncer-
enough timescales, however,
address them, especially with tainties due to natural variabil-
even the most stable engi-
regard to the R&D programme, ity, and randomness – and the
neered materials and geolog-
in order to eventually arrive at concept of uncertainty classifi-
ical environments are subject
a safety case that is adequate cation is both widely used and
to perturbing events and
for licensing. Explicit treatment judged as necessary for per-
changes that are subject to of uncertainties is thus an forming uncertainty analyses.
uncertainties. The uncertainties essential part of building confi- One part of the overall uncer-
associated with the evolution dence in the safety case. Con- tainty management process is
of the disposal system have to fidence in the safety case is the evaluation of quantifiable
be appropriately considered supported by a reliable safety uncertainties in a quantitative
and managed throughout a assessment with a clear state- assessment of system perform-
repository development pro- ment on data quality, clear jus- ance. However, since not all
gramme. tifications of assumptions and uncertainties can be quantified,
At each stage of a stepwise discussion of the sensitivities of the use of other elements of
development programme, deci- the system performance to information making up a safety
sions should be based on uncertainties. The uncertainties case, such as complementary,
appropriate levels of confi- and the potential for reducing qualitative lines of evidence,
dence about the achievability them in subsequent develop- will also contribute to the
of long-term safety, with the ment phases should therefore uncertainty management
* Dr. Björn Dverstorp, of the Swedish Institute for Radiation Protection (SSI), was the Chair of the workshop on Management
of Uncertainty in Safety Cases and the Role of Risk. Dr. Abe Van Luik, of the US Department of Energy (US DOE) was Chair of
the NEA Integration Group for the Safety Case (IGSC) from 2000 to 2004. Dr. Hiroyuki Umeki, of the Japan Nuclear Cycle
Development Institute (JNC) has been Chair of the IGSC since the end of 2004. Ms. Sylvie Voinis, of the NEA Secretariat, is in
charge of the IGSC Scientific Secretariat. Dr. Roger Wilmot is from Galson Sciences.
14 NEA updates, NEA News 2005 – No. 23.1process (NEA, 2004). Uncer- how uncertainties should be be confidence in the analy-
tainty management consists of treated in a safety case: sis of performance and asso-
understanding the potential ● The safety case informs ciated uncertainties.
implications of uncertainties, decisions at each stage of a
and in some cases planning to step-by-step decision-making The 2004 workshop on
minimise these potential effects process. There is therefore a
through the site selection the management of
trend towards safety cases
process and design adapta- uncertainty
providing a statement on
tions. Other issues, including why there is confidence in To build upon the lessons
policy, social context, availabil- the results presented, and learnt from the earlier activities
ity of resources and decision- on the sufficiency of the and workshops and to provide
making timetables, also affect safety case for the decision a forum for a focused discus-
choices. at hand. With that perspec- sion on the handling of uncer-
The presentation of a safety tive, such a statement tainty and risk, the Integration
case will place most emphasis should acknowledge the Group for the Safety Case
on the evaluation and argu- existing uncertainties, their (IGSC) decided to organise a
mentation of the expected significance at the present workshop on the Management
performance of a waste man- stage of assessment, and the of Uncertainty in Safety Cases
agement facility. However, future steps required to and the Role of Risk. The work-
making the case for the reduce uncertainty. shop was held in Stockholm
expected performance requires ● Uncertainties should be
on 2-4 February 2004 and
an illustration of performance recognised as an inevitable hosted by the Swedish Institute
in its uncertainty context while aspect of radioactive waste for Radiation Protection (SSI).
taking into account the current management systems, and The overall aim of the work-
stage of system development. these uncertainties will shop was to create a platform
increase with the timescale in order to better understand
considered. different approaches to manag-
Previous NEA activities
ing uncertainty in post-closure
on uncertainty issues ● Uncertainties should be
safety cases and regulatory
treated explicitly, and a sys- approaches in different
One of the earliest NEA
tematic approach will aid national waste management
activities on uncertainty issues
understanding. programmes. The aims of the
was a meeting in Seattle in
1987 at which the importance ● A combination of deter- workshop were:
of treating uncertainties in ministic and probabilistic ● to identify common elements
assessments of post-closure approaches may be appro- in different approaches to
performance of disposal facili- priate. Decision making is managing uncertainty;
ties was highlighted. This early not based on a numerical
● to discuss different approaches
recognition of the issue was value for uncertainty, and
there is a need to clarify the to setting regulatory standards
developed through a series of for regulatory review;
NEA meetings and workshops role of each approach in the
safety case. ● to facilitate information
in subsequent years. The
Probabilistic Safety Analysis ● A range of scenarios needs
exchange and to promote
Group (PSAG) played an to be considered in order to discussion on different techni-
important role in encouraging explore uncertainties. The cal approaches to the manage-
debate of different approaches, issue of human intrusion has ment and characterisation of
and also organised a series of a special place within the uncertainty and on the role of
scenarios considered. risk;
code inter-comparison exer-
cises (NEA, 1997a). Other key ● to explore the merits of alter-
● A range of arguments is
activities include initiatives by native approaches to risk-
important in treating uncer-
the Integrated Performance informed decision making;
tainties and developing a
Assessment Group (IPAG) and
safety case. In particular a
(NEA, 1997b, 2002a); work- mixture of quantitative and ● to identify the potential for fur-
shops on confidence building qualitative arguments will ther developments of methods
(NEA, 1999) and the handling engender confidence in or strategies to support the
of timescales (NEA, 2002b); both the provider and the management of uncertainties.
and the ongoing development reviewer. Overall, the safety The NEA prepared a synthe-
of the Safety Case Brochure case can best fulfil the sis of the workshop, which was
(NEA, 2004). requirements of decision published in proceedings (NEA,
These activities have led to making by including a state- 2005). The main findings may
some broad conclusions about ment on why there should be summarised as follows.
Management of uncertainty in safety cases and the role of risk, NEA News 2005 – No. 23.1 15What is risk? analysis”, refers to the meth- the importance of treating
Diversity definitions are ods used in the field of both uncertainty whatever the regu-
sometimes adopted for terms nuclear and non-nuclear indus- latory end-point. Although
such as “risk”. The word “risk” try, to identify potential expectations regarding the
could be interpreted as having sources of danger and rank evaluation and presentation of
different meanings for different them in terms of importance. uncertainties do vary depend-
The following additional ing on the end-point used,
definitions were suggested: there are similar expectations
regarding the use of support-
● risk-based approach: “regu-
ing arguments, transparency
latory decision making
and traceability, justification of
solely based on the numeri-
assumptions and other qualita-
cal results of a risk assess-
tive aspects of treating uncer-
ment”;
tainties, whether the end-point
● risk-informed approach:
is dose or risk.
“risk insights considered
Regulators see interactions
with other factors”;
with implementers ahead of
● deterministic approach: “the
the licensing process as an
use of fixed values in mod- opportunity to identify critical
elling for characterisation of issues, to resolve differences in
uncertainty”; approach and to reduce the
● probabilistic approach: resources and time required for
“characterisation of uncer- review of a license application.
end-users (nuclear power tainty with probabilistic dis- Overall, regulatory expecta-
plants, waste management tribution functions as input tions are for safety cases that
organisations...), and a set of to modelling”; are risk-informed rather than
characteristics for which alter- ● risk: “consequence times risk-based.
native approaches or view- probability of occurrence”.
points exist: objectivist/realist Assessment of uncertainty
A general observation from
(regards risks as real) vs. con- and risk
the workshop discussions was
structionist (regards risk as a
that differences in the interpre- All assessments must address
mental construct); quantitative
tation of key terms and con- the components of the risk
vs. qualitative; and different
cepts may hamper a good triplet: What can happen?
mathematical formulations [e.g.
discussion and understanding What are the consequences?
probability times consequence;
of the national regulatory and and What is the likelihood?
expected (negative) utility; and
assessment approaches. Hence, Approaches differ in the extent
open formulations]. For techni-
it was concluded that clear def- to which probabilities are
cal experts, “risk” often means
initions, when making a safety assigned explicitly (e.g., as
the product of probability and
case, are key to a successful probability density functions)
consequence. In public discus-
dialogue with various stake- or implicitly (e.g., through the
sion risk may mean only the
holders. selection of likely and less
probability (of a negative con-
sequence), although the con- likely scenarios). The explicit
sequences may be of most Regulatory approaches use of probabilities to charac-
interest to the public. Both There is no simple distinc- terise uncertainty is not
“constructed” (perceived) risk tion to be made between regu- restricted to calculations of
and “realist” risk do matter and lations with risk or dose risk. Overall, there is a role for
the public may be concerned criteria. In particular, regula- deterministic and probabilistic
about both. As an example, in tions requiring the calculation calculations in both risk- and
Andra’s usage, “risk” is defined of dose for the normal or non-risk-oriented assessments.
as the characterisation of a expected evolution may A key difference between
potential danger in terms of require an assessment of risk the alternative approaches to
both probability and impor- for less likely scenarios. Also, the treatment of uncertainty is
tance. The product of both is regulatory guidance requiring the extent to which uncertain-
rarely considered. Therefore, the calculation of risk for natu- ties are aggregated or disaggre-
such expressions as “the prob- ral events and processes may gated. Disaggregated analyses
ability of a risk” or “the impor- not require an assessment of are of value for developing
tance of a risk” refer to two probabilities for human intru- detailed system understanding
independent variables. “Risk”, sion scenarios. Regulators have and providing information for
in such expressions as “risk similar expectations regarding design choices and research
16 NEA updates, NEA News 2005 – No. 23.1You can also read
