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

5

• 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

0

200

400

600

P

, kП

a

эксперимент

расчет

0 1 2 3время, с

0

200

400

600

P

, kП

a

эксперимент

расчет

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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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