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Prevention and Mitigation —
Equal Priorities
Prof. Vladimir Asmolov
WANO President
International Experts’ Meeting on Reactor and Spent Fuel Safety in the Light of the Accident
at the Fukushima Daiichi Nuclear Power Plant
19 -22 March 2012, Vienna, Austria
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Phases of Nuclear Power Development
in Post-Chernobyl Period
1986 – 2004 - the ―survival‖ period
2004 – 2008 - nuclear ―renaissance‖
2008 – 2009 - global financial crisis
2010 – March 2011 - end of recession periodand post-crisisdevelopment
11 March 2011 - Fukushima accident
2011 onward - Post-Fukushima actions
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State-of-the-art in Nuclear Power Engineering
(high degree of globalization)
Five countries (U.S.A., France, Japan, Russia and Germany) altogether produce 70% of nuclear-generated electricity in the world.
Light water reactors of three types (PWR, BWR, VVER) represent 80% of global reactor fleet.
Five countries (Russia, France, Japan, China, India) are developing fast reactor technologies in an advanced phase.
Six companies (Rosatom, URENCO, USEC, EURODIF, CNNC, JNFL) are performing commercial-scale uranium enrichment.
Six countries (France, United Kingdom, Russia, Japan, China, India) have nuclear fuel reprocessing capacities.
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TMI1979
1986Chernobyl
2011Fukushima
1989
WANO basic working principles:- voluntariness;
- collective responsibility;
- independency, and
accountability to members only;
- confidentiality.
WANO today:
- new challenges;- Mitchell’s Commission.
WANO: Main development milestones
Purpose of the Commission
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The WANO Post Fukushima Commission
was formed in April 2011 with a mission to:
―…recommend changes to WANO’s programs
and structure to effectively implement lessons
arising from the Fukushima Daiichi nuclear accident;
and in doing so, to increase the nuclear safety of
nuclear power plants and fuel processing facilities
worldwide.‖
Commission Charter
Commission Strengths
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Experience and Expertise
O. Allan Kupcis
Past Pres. WANO
Former CEO
Ontario Hydro
John Herron
Pres., CEO and CNO
Entergy Nuclear
Yuriy Nedashkovskiy,
President, SE NNEGC
Energoatom
Vladimir Asmolov
First Deputy General
Director
Rosenergoatom Concern
OJSC
Tom Mitchell, Pres.
and CEO
OPG
Mgr. Ing. Vladimir
Hlavinka
Chief Production Officer
CEZ a.s.
Dominique Miniere,
Executive Vice President
EDF
William (Bill) Coley,
former CEO, British
Energy; former
Pres. Duke Power
Philippe Van Troeye
General Manager of
Generation, Belgium
& Luxembourg
Electrabel
Jörg Michels
Executive Director
ENBW
Kernkraft GmbH
Takao Fujie,
Pres. and CEO
JANTI
Hyun-Taek Park
EVP and CNO
KHNP
Hideki Toyomatsu
Director, EVP and CNO
Kansai Electric Power Co.
GAO Ligang,
Senior Vice President
China Guangdong Nuclear Power
Holding Company (CGNPC)
Photo
Unavailable Photo
Unavailable
Commission Strengths
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Major Companies/Organizations Represented
Commission Strengths
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International Composition
Russia
U.S.A.
Canada
Japan
Ukraine
South Korea
Czech Republic
France
BelgiumChina
Commission Strengths
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All WANO Regions Represented
Atlanta Centre
• Ontario Power Generation
• Entergy
Moscow Centre
• CEZ, a.s.
• Concern Rosenergoatom
• NNEGC Energoatom
Paris Centre
• CGNPC
• Electricité de France (EDF)
• EnBW Kernkraft GmbH (EnKK)
• Electrabel
Tokyo Centre
• Japan Nuclear Technology Institute
• Kansai Electric Power Co., Inc.
• Korea Hydro & Nuclear Power Co.
Commission’s Scope
Meetings in:
Atlanta
Paris
Seoul
Prague
Tokyo 10
KNOWLEDGE
BASE
TECHNOLOGY(technical safety ensuring)
DEFENCE
IN-DEPTH PRINCIPLE
Multiplicity of safety
barriers
Variety of levels for
protection barriers:
- prevention of accidents
- mitigation of accident
consequences
(accident management)
LEGISLATION
Federal laws
(responsibility principles)
System of rules and
regulation
State licensing authority
(independent regulation)
SAFETY CULTURE- Alignment of priorities
- Human factor
Accident lessons learned
SAFETY FUNDAMENTALS
The safety fundamentals are correct and
shall not be subject to any revisions
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The main Lessons
Learned
Availability of undamageable
portable engineering means
for power and water supply in
the conditions of NPP isolation
Prompt actions of:
- responsible and powerful utility;
- trained personnel.
The key criterion of success:
- recovery of power supply
- water feed for the decay heat removal
As prompt as possible!
Accident lessons learned
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Commission Recommendations
Fukushima Related
Expand the scope of WANO programs
Promote and implement a worldwide,
integrated nuclear industry event
response
Performance Gap Related
Achieve peer-review performance
improvement within four years
Become more publicly visible
Conduct periodic internal peer reviews
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WANO Post-Fukushima
Commission
Final Report
September 30, 2011
Expanding the scope of WANO programmes(Peer Reviews, TSM, Training) to address:
Member emergency preparedness fundamentals
Severe accident management, including procedures, training and readiness
Fuel pool and fuel storage cooling and contingencies
Multiple unit impacts and considerations for mitigation
Implementation of design safety fundamentals for the prevention of fuel damage and mitigation ofoff-site radiation release and public impact
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WANO scope expansion
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Enhancement of WANO Peer Reviews
• Priority in recommendations is given to SAFETY1• Review of the accomplished modernization
measures focused on safety improvement2• Assessment of the NPP reaction to the severe
accidents occurred3• Assessment of emergency preparedness:
- on-site- off-site
4• Striving to an attitude of obligatory
implementation of recommendations related to Areas For Improvement
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• Assessment of the design base readiness to any new challenges6
Fundamental change of WANO
competence after Fukushima
• The highest priority – to prevent accidents
Before the
2011 event
• Equally high priorities – accident prevention and accident mitigation:- implementation of design fundamental;- emergency preparation;- SA management.
After the 2011 event
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EQUAL PRIORITY OF THE
SAFETY ENSURING GOALS
1. The accident prevention
– Quality of design, justification of design solutions
– Self-protection – inherent safety features
– Taking into account both internal and external initial events
– Quality assurance at all stages of construction, operation and decommissioning
2. The accident management
– Development of measures to mitigate the accident consequences, that is, measures focused on retention of safety barriers integrity
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Implementation of design safety fundamentals for the prevention of core damage accident:
Evaluation of design features to determine the area of safety improvements based
on operating experience
Corrective actions
Safety modernization during the whole plant life time
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Defense-in-depth
Mitigation (accident management):
Training of personnel
Verifying key elements of emergency response procedures
Sharing of operating experience and good practices
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Defense-in-depth (cont.)
What we know today about severe accident phenomena?
(Knowledge base after TMI, Chernobyl and Fukushima)
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Accident prevention(for all possible initial events NPP design shall justify that destruction limits for fuel elements would not be exceeded)
Impossibility to take accident management measures
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REACTIVITY ACCIDENTS
DIFFERENT MODES OF FUEL ROD FAILURE
FAILURE OF FUEL CLADDING
Cladding crimping at
fuel pellet edge locations
Cross-section of thefuel element in the
maximum deformationarea
Specific bulgewith the cladding destruction
FRAGMENTATION
OF THE FUEL ELEMENTS
Bottom plugwith solidificatedmelt
Fragments of the fuel pelletswith melted-out central part
High burnt-up
(left) and fresh (right)
fuel elements
REACTIVITY INITIATED ACCIDENT
Testing of fresh and burnt upfuel rods in the GIDRA, IGR
BIGR pulse reactors
FAILURE THRESHOLDDATA BASE
Mechanical testingof specimens in
hot cell
MECHANICAL PROPERTYDATA BASE
neutronics hydraulics
Development of dynamic computer code
coupled withthermo ;fuel rod thermo-mechanics.
Analysis of possible accident scenarios
COMPUTATIONSCENARIO CATALOG
NPP SAFETY JUSTIFICATIONUNDER RIA CONDITIONS
Testing of fresh and burnt up fuel rods in the
GIDRA, IGR, BIGR (Russia), Cabri(France), NSRR
(Japan)
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ACCIDENTS WITH LOSS OF CORE
COOLING FUNCTION
Progression of an accident
with loss of core cooling function at a nuclear plant is a sequence of plant states, each of them being more severe as compared to a preceding one due to a greater degree of safety barriers damage
TMI-2
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Sequence of States
(phases) of Accident Progression:
Containment damage, fission
products release to the environment
Reactor vessel damage,
melt release into the containment
Core melting, relocation of molten core
to reactor vessel lower head,
formation of molten pool
Loss of efficient reactor core cooling
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For each severe accident state its own safety specific
goal should be determined, and the accident
management strategy and methods shall be focused on
achievement of that goal:
Prevention of fuel damage
Molten fuel retention inside
the reactor vessel
Prevention of the containment damage
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PROCESSES AND EVENTS ACCIDENT
MANAGEMENT GOAL
ACCIDENT MANAGEMENT
MEASURES
To prevent the core melting (To keep the integrity of the I
st
and IInd
physical barriers)
The recovery of the core cooling
I phase
REACTOR CORE DEGRADATION
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SEVERE ACCIDENT PROGRESSION AT A NPP
CORA – PWR, BWR, VVER PROGRAM
KEY PROCESSES
• Core dry out and overheating
• High temperature oxidation of fuel claddings
• Fuel-cladding interaction
• Hydrogen generation
• Melting and relocation down of core materials
• Blockages formation
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PROCESSES AND EVENTS ACCIDENT
MANAGEMENT GOAL
ACCIDENT MANAGEMENT
MEASURES
To retain melt inside the RPV (To keep the integrity of the III
rd physical
barrier)
In-vessel cooling
Ex-vessel cooling
II phase
REACTOR PRESSURE VESSEL DAMAGE
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SEVERE ACCIDENT PROGRESSION AT A NPP
RASPLAV, MASCA PROJECTS
Data base was obtained on the melt
thermal-physic properties under the
temperatures up to 3100К
Data base was created describing the key
parameters for the melt pool behaviour
Computational tool was developed
RASPLAV MASCA
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PROCESSES AND EVENTS ACCIDENT
MANAGEMENT GOAL ACCIDENT MANAGEMENT
MEASURES
To prevent the containment failure (To keep the integrity of the IV
th physical
barrier)
Development of the core catcher Development of hydrogen safety system Filtered venting system
SEVERE ACCIDENT PROGRESSION AT A NPP
III phase
CONTAINMENT DAMAGE
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STUDIES OF HYDROGEN
DEFLAGRATION AND DETONATION
Criteria for the modes of theflame propagation have beendeveloped
Gas-dynamic computercodes have been developed(turbulent deflagration anddetonation of gas mixtures)
Hydrogen safety systemshave been developed
0 1 2 3время, с
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400
600
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эксперимент
расчет
0 1 2 3время, с
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SEVERE ACCIDENT KNOWLEDGE BASE SUMMARY
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Implementation of a unified
methodology for severe accident management
1. Definition of safety goals for every phase of
accident progression (safety goals tree)
2. There are safety functions that ensure achievement
of the defined goals
3. Loss of such a function leads to a request on its restoration
4. Based on knowledge of specific parameters of the emergency process a relevant effective procedure of accident management is selected
5. Assessment of preparedness to manage an accident effectively (evaluation of the knowledge level) shall produce a request on additional investigations
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Additional study based on peer reviews and operation experience
Filtered containment venting
Prevention of hydrogen deflagration and detonation
Prevention of steam explosion
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KNOWLEDGE BASE
(request for additional research))
Deterministic experience related
to BDBA consequences evaluation
The equipment additional failures
Methodology for the analysis
of NPPs robustness to the severe accidents
Reliability
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NPP1) Total loss of:
- electric power supply;
- core cooling;
- coolant sources
2) Loss of primary
circuit integrity
3) No operator’s accident
management actions
Fire
First step in the robustness analysis
Evaluation of time to degradation of safety barriers on the path of radioactive fission products’ dispersal due to sequential failure of safety functions of regular systems and unsuccessful accident management actions
Decay heat removal to the final absorber
Reactor core components integrity
Main coolant circulation circuit integrity
Leak-tight compartments integrity
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1.5 – 2 hours In case of LOCA – for VVER-1000 NPPs
5-6 hours In case of absence of LOCA – for VVER-1000 NPPs
24 hoursIn case of LOCA – for Tianwan NPP, Kudankulam NPP, AES-2006
72 hoursIn case of LOCA – for VVER-TOI
As long as necessaryIn case of absence of LOCA – for Kudankulam NPP, AES-2006, VVER-TOI
Time reserves before reactor core destruction
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1
• NPP design quality and using operating experience accumulated as much as possible (accident prevention)
2
• A consistent fight for retention of integrity of physical safety barriers while every barrier being considered as a last one on the way of the melt propagation (accident management)
The accumulated knowledge of severe accident
processes and phenomena allow us to solve
the problem of severe accident management
by means of:
Implementation of the severe accident management allows us to proceed to the second step of the robustness analysis
Cost-benefit analysis
Estimation of reasonableness of investments into the hazard reduction
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Second step in the robustness analysis
Suggestions to WANO
To develop and implement a mutually recognized generic methodology for analysis of the Defense-in-Depth robustness for different reactor types
To develop additional peer review subprogrammes focused on reviewing of effectiveness of the measures aimed at increasing the existing NPPs robustness to abnormal events
To consider a possibility to establish regional emergency response centres according to reactor types for provision assistance to operating organizations
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Cooperation Between IAEA and WANO
At the WANO BGM in Shenzhen in October
2011, Director General Amano called for
greater cooperation between WANO and IAEA
IAEA Fukushima action plan and WANO action
plan both call for greater cooperation
Revised Memorandum of Understanding
(MOU) is being drafted
Nuclear safety is best served by a strong
WANO and a strong IAEA
From Richard Meserve’s letter addressed to the IAEA Director General Yukiya Amano:
1. The operator must have engineering and financial capabilities
end management authority to ensure its responsibility;
2. The nuclear regulator must have necessary authority, and
sufficient financial and qualified human resources to fulfill its
responsibilitie;
3. Constructive interaction between regulators and operators is
important;
4. A clear delineation of responsibilities must exist between the
management structure of the operator, the regulator, and the
governmental authorities;
5. A NPP design shall be resistant to any external beyond-design-
basis impacts and allow to maintain key safety functions after
the beginning of an accident.
Involvement in INSAG activities
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Areas of Possible Cooperation
Between WANO and IAEA
1. New entrants to our industry
2. Common definition for performance
indicators
3. Sharing resources between peer reviews
and OSARTs
4. Sharing generic issues and trends identified
from data reviews
5. Supporting each others working groups
(example: review of IAEA safety standards)
6. Attend INSAG meetings
1. Widen the involvement of representatives of operatingorganizations in TWGs and SAGNE.
2. Expand the representation of high level experts fromoperating organization in INSAG to intensify feedbackfrom operating organizations and their experience insafety.
3. Enhance communications between SAGNE and INSAG.
4. Strengthen the Agency’s capabilities to collect anddisseminate the best operational practices.
5. Strengthen the Agency’s cooperation and collaborationwith WANO.
6. Facilitate interactions between operating organizations ofexperienced countries and newcomers.
7. Open wider communication of operating organizationswith public though IAEA communication tools.
Recommendations to IAEA
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Closing Thoughts
Fukushima will offer important industry lessons, but
the safety fundamentals are correct and shall not be
subject to any revisions
Human performance (safety culture) is still the
leading cause of core damaging events
Our industry (and WANO) must shift its mindset from
―prevention‖ to ―prevention and mitigation‖
Our industry (and WANO) will emerge from the
Fukushima event with an even stronger commitment
to nuclear safety
1. Nuclear safety is not based only on regulators. Theprime responsibility for nuclear safety rests withoperating organizations which have the necessaryexperience and knowledge.
2. Improvement in safety can be reached through bettersharing of operation experience and improvements intechnology. The IAEA is to increase interactions withutilities and nuclear industry.
3. The IAEA should declare clearly the recognition of therole of operating organizations and nuclear industryin safe, efficient and sustainable nuclear powerdevelopment and to strengthen cooperation withthem.
Conclusions
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