Safety and harmonization of approaches to safety in future innovative systems from

view-point of technology user

Saleem A. Ansari

Directorate of Nuclear Power Engineering Directorate of Nuclear Power Engineering ––

ReactorsReactorsPakistan Atomic Energy Commission

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INPRO Dialogue Forum WorkshopINPRO Dialogue Forum Workshop(Feb 1 (Feb 1 --

4, 2010)4, 2010)

Nuclear Energy Projection

Nuclear energy supplied about 16% of the world electricity needs at the end of the 20th century

Projected nuclear power generation for year 2030 (EIA, DOE)-

Projection made in 2005: 374,000 MWe

-

Projection made in 2008: 498,000 Mwe

IAEA Projection for 2030:

650,000 MWe (Akira OMOTO, 2006)

Projected growth is equivalent to 124 new 1,000-MW reactors.

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Drivers of Nuclear Power Development

• The most important drivers of nuclear power are:

–

Scarcity of local energy resources

–

High expected electricity demand growth

–

Need to reduce greenhouse gas emissions.

• Important:

For nuclear power to be a viable option, nuclear industry should strive to be economically competitive with other electricity generation options without

relying on these “external factors”

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Need for Sustainable Energy Development

Brundtland Report (Our Common Future)

In 2001, IAEA introduced the INPRO Mission for sustainable

growth of nuclear energy. The INPRO

Objectives and INPRO Methodology were defined

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Sustainable development is a development that meets the needs of the present without compromising the ability of future generations to meet their own needs

INPRO Mission International Project on Innovative Nuclear Reactors and Fuel Cycles

To provide a forum for discussion by bringing together both technology holders and technology users to consider jointly the actions required to achieve desired innovations in nuclear reactors and fuel cycles

To develop the methodology to analyze INS (Innovative Nuclear System) on a global, regional and national basis

To facilitate coordinating and collaboration among member states

for

planning of development and deployment of INS

To pay particular attention to the needs of developing countries

interested in INS

[Akira OMOTO, DNP, IAEA; November 2006]5

The scope of the INPRO project covers nuclear reactors

expected to come into service in the next 50-100 years and

beyond. It is expected that a mixture of existing,

evolutionary, and innovative designs will be brought into

service and coexist within this period

Scope of INPRO Project

Scope of INPRO ProjectScope of INPRO Project Why is Why is Nuclear Safety Significant in INES ?Nuclear Safety Significant in INES ?

No. of NPPs expected to operate in next 50 years will increase considerably over the present number.

If safety of INES ≈safety of operating systems today, there is an increase in numerical risk of nuclear accidents (4 in 50 y).

To bring down this no. to 1 in 50 y, a ten-fold reduction in likelihood of a serious reactor accident (core damage frequency of 10-6

reactor-years) is a desirable goal in INES.

INPRO methodology Objective: Increase in calculated risk would be compensated by increased safety level of NES on lessons learned from systems in operation.

• Two stimulants for growing share in world energy needs: Population growth and economic development

• Share of developing countries in NE is limited:

Insufficient infrastructure and small electricity grids.

Limited investment capability to invest in capital intensive nuclear projects.

Implementation of nuclear power has a longer timeline than most other commonly used electricity generation options.

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Nuclear Power and Developing CountriesNuclear Power and Developing Countries

Elements of NPDC for developing countries:

� National energy planning� Comparative economic assessment of nuclear power� Establishment of nuclear regulatory body, licensing regulations and

applicable codes and standards—

Human resource development

— Nuclear technology selection

.

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Nuclear Power Development CycleNuclear Power Development Cycle

Nuclear Power Development Cycle Nuclear Power Development Cycle (contd.)

— Site selection and environmental assessment

—

Development of integrated management system of safety, QA, waste management strategy etc.

— Preparation of URD, Bid Specification & Bids Evaluation

— Conclusion of commercial and financing contracts

— Plant construction and commissioning

— Operation and Maintenance

— Lifetime technical support to operating plants

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• Centre of nuclear activity has shifted from North America and Western Europe to South and East Asia.

• Out of the last 40 nuclear plants connected to energy grids since 1995 around the world, 28 have been built in China, Japan, Korea, Russia, India and Pakistan.

• There are 133 nuclear plants in operation in East and South Asia with 25 more under construction and another 40 planned.

• A large no. of developing countries are eager to install NPPs.

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There is Hope for Developing Countries

Elements of Elements of Sustainable Sustainable Nuclear Nuclear Energy Energy GrowthGrowth

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The Generations of NPPs

Advanced Reactor Concepts Advanced Reactor Concepts

The range of reactor systems having advanced or innovative design features includes:

water-cooled,

gas-cooled,

liquid metal-cooled systems and

molten salt reactors of various sizes to be used for various purposes.

According to some estimates, by 2050, two thirds of the NES will be LWRs, with remaining one third could be filled by HTGR and other reactor types

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Economic Benefits of Innovative Nuclear Systems

• Many nuclear design institutes have been working on Gen-III & Gen-IV plants: Large NPPs ( > 1000 MW); SMRs

• INS can effectively meet demands of lower costs, fuel sustainability and safety

• GE, WH, & AECL claimed that cost of their advanced reactor models were comparable with coal plants

• Increased costs of first-of-a-kind engineering effects however, must be considered for the first few plants of any given new model.

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INES INES

and and

Technology User CountriesTechnology User Countries

Technology & Safety ApproachesTechnology & Safety Approaches

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What to Select ?Large vs. Small & Medium Reactors (GEN-III/III+)

Parameter SMR (300-700 MW) Large (>= 1000 MW)

Cost Economics Medium Good

Availability limited universal

Infrastructure Requirement

Works with small or localized grid. Provide the flexibility of power generation. modular design provides incremental capacity increase.

Large/integrated grid; Large cooling water requirement; Vast EA & LPZ areas; Safety & Waste management issues

Safety High High

Human Resource Requirement

No substantial difference from large plants

A few hundred engineers/ technicians required

Licensing Requirement

No substantial difference Regulatory authority should cope with innovative designs

Proven Technology Yes for Gen-III

Expectations from NES: Design & Safety

Simplicity in design through reduced number of components

Simplicity in Safety through use of passive safety systems

Conformance of design to latest codes & standards

Shorter construction periods

Plant sizes suitable for various grid capacities and owner investment capabilities -

Large as well as SMRs

Proven design as well as new approaches to safety improvements

Severe accidents with late containment failure scenario

Rigorous Safety Analysis to analyze accident consequences

Digital C & I to reduce volume of cables and instrumentation

Advanced techniques for plant life management

A design life of 60 years;

High plant availability; short RFOs; 24 M operating cycles

Increased margins to reduce sensitivity to disturbances Improved automation and HMI

HMI & increased margins to provide more time for the operator to

act in accident/Incident situations

Core damage frequency less than 10-5

per reactor-year

Cumulative frequency of large releases <10-6

per reactor-year

Design measures to cope with severe accidents.

Expectation form NES: Users Requirements

(IAEA Report on Common User Considerations by Developing Countries for

Future Nuclear Energy Systems, 2009)

The safety of future plants will build on experience in achieving the high levels of safety of current plants. The new nuclear power plant designs currently under development incorporate various technical features to meet very stringent safety requirements

Approach towards safety of INES

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INES must meet Nuclear Safety Objectives & Radiation Protection Objective

General Safety ObjectiveTo protect individuals, society, and environment from harm by establishing and maintaining in nuclear facilities effective defenses against radiological hazards

• To ensure that in all operational states radiation exposure within the facility or due to any planned release of radioactive material from the facility is kept below prescribed limits and as low as reasonably achievable, and

• To ensure mitigation of the radiological consequences of any accidents.

Radiation Protection Objective

• To take all reasonably practicable measures to prevent accidents in nuclear facilities and to mitigate the consequences of any accidents that do occur,

• To ensure with a high level of confidence that, for all possible accidents taken into account in the design of the facility, including those of very low probability, any radiological consequences would be minor and below prescribed limits, and

• To ensure that the likelihood of accidents with serious radiological consequences is extremely low.

Technical Safety Objective

Safety Approach to INES

Public acceptance by safety enhancement

Strengthen safety regulation; Defence-in-depth

Introduction of rigorous QAPs for plant design, licensing, construction and operation

Improvements in seismic design and qualification of buildings

Attention to the effect of internal and external hazards

Reducing the likelihood of accidents through design, surveillance & operational means

Consideration/management of severe accidents

To ensure that the safety equipment performs three fundamental functions: control reactivity; remove heat from the core; and confine radioactive materials and shield radiation

To take all reasonably practical measures to prevent accidents

To mitigate their consequences, should they occur

To ensure, by analysis, for all possible DBAs any radiological consequences would be minor or below prescribed limits

To ensure that the likelihood of accidents with serious radiological consequences is extremely low.

Nuclear Safety Objective & INES

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Fuel Pellet

Fuel Cladding

Pressure Vessel

Steel Liner

Shield BuildingPhysical Barriers

Safety Approach to INESSafety Approach to INES Strategy of DefenseStrategy of Defense--inin--DepthDepth

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Strategy of Defense-in-Depth

Inherent Safety

Precaution

Beyond DBA

Mitigation

Prevention

Negative Reactivity Feedback

Reactor ControlSystem

Reactor ProtectionSystem

Engineered SafetyFeatures

Severe AccidentPrecaution/Coping

+

+

+

+

EventFrequency CDF

Systematic Barriers

Safety Approaches to INSSafety Approaches to INS

Safety Enhancement in INES through Defence-in-Depth

Older Plants INES

Level -1 Prevention of Abnormal operation and failures

Prevention of Abnormal operation and failures.

Enhance prevention by increased emphasis on inherently safe design characteristics and passive safety features, and by further reducing human actions in the routine operation of the plant.

Level -2 Control of abnormal operation and detection of failures

Control of abnormal operation and detection of failures.

Give priority to advanced control and monitoring systems with enhanced reliability, intelligence and the ability to anticipate and compensate abnormal transients.

Level -3 Control of accidents within thedesign basis.

Control of accidents within the design basis.

Achieve fundamental safety functions by optimized combination of active & passive design features; limit consequences such as fuel failures; minimize reliance on human intervention by increasing grace period, e.g. between several hours and several days.

Older Plants INS

Level -4 prevention and mitigation of consequences of severe accidents

Complementary measures and accident management

Increase reliability and capability of systems to control and monitor complex accident sequences; decrease expected frequency of severe plant conditions; e.g. for reactors, reduce severe core damage frequency by at least one order of magnitude relative to existing plants and designs, and even more for urban-sited facilities.

Level -5 Mitigation of radiological consequences of significant releases of radioactive materials

Off-site emergency response

Avoid the necessity for evacuation or relocation measures outside the plant site.

Safety Enhancement in INES through DefenceSafety Enhancement in INES through Defence--inin--DepthDepth

Safety Analysis for INES : Safety Analysis for INES : OPs & EOPsOPs & EOPs

Routine operations

Accident conditions

Alarm response Procedures

Abnormal operating Procedures

Emergency operating Procedures

Severe accident Procedures

Hierarchy of plant procedures for various operating conditions should be well planned

System Operating Procedures

Requirement of Safety Analysis for INESRequirement of Safety Analysis for INES

There should be an optimum combination of deterministic and probabilistic approaches for safety analysis.

Computer codes used in DSA must be benchmarked for reliable analytical results acceptable to the regulator.

Uncertainties in probabilities in PSA should be resolved based on well established data.

Categorization of following initiating events be considered in SA.

Increase in heat removal by the secondary side

Decrease in heat removal by the secondary side

Decrease in flow rate in the reactor coolant system

Increase in flow rate in the reactor coolant system

Anomalies in distribution of reactivity and power

Increase in reactor coolant inventory

Decrease in reactor coolant inventory

Radioactive release from a subsystem or component 30

Accident Scenarios for SEOPs in INESAccident Scenarios for SEOPs in INES

Attention should be given for the background safety analysis of Attention should be given for the background safety analysis of following accident scenarios in SEOPs following accident scenarios in SEOPs

Loss of Offsite PowerLoss of Offsite Power

Steam Generator Tube RuptureSteam Generator Tube Rupture

Small Break Loss of Coolant AccidentSmall Break Loss of Coolant Accident

Large Break Loss of Coolant AccidentLarge Break Loss of Coolant Accident

Steam Line Break AccidentSteam Line Break Accident

Loss of FeedwaterLoss of Feedwater

Anticipated Transients without ScramAnticipated Transients without Scram

Pressurized Thermal ShockPressurized Thermal Shock

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Improved Measures for INES SafetyImproved Measures for INES Safety

Simplicity in safety action: In the event of a design: In the event of a design--basis accident, the basis accident, the plant should achieve and maintain safe shutdown condition withouplant should achieve and maintain safe shutdown condition without t dependence on operator action or standby power. Grace period > 1dependence on operator action or standby power. Grace period > 1

day day

to reduce the burden on operators in case of accidents. Passive to reduce the burden on operators in case of accidents. Passive safety safety systems are good choice. These include: systems are good choice. These include:

-- Passive core cooling systemPassive core cooling system; ;

-- Containment isolation;Containment isolation;

-- Passive containment cooling system; Passive containment cooling system;

-- Main control room emergency habitability system Main control room emergency habitability system

Passive systems may be supplemented with active systems for addiPassive systems may be supplemented with active systems for additional tional defensedefense--inin--depth. (CVCS; RHRS; Auxiliary feedwater)depth. (CVCS; RHRS; Auxiliary feedwater)

(contd(contd…….).)

Improvements in Safety of INESImprovements in Safety of INES (contd.)(contd.)

IVR by external reactor vessel cooling and Cavity Flooding IVR by external reactor vessel cooling and Cavity Flooding System to be employed for System to be employed for InIn--vessel Retention of Core Damagevessel Retention of Core Damage

Passive Auto-catalytic Recombiners (PAR’s) for hydrogen control

Motorized throttle valve at pressurizer to avoid high pressure melt ejection (HPME)

Anti-dilution protection signal (ADP) as countermeasure for heterogeneous boron dilution (for LWRs)

Safety Considerations in INES Safety Considerations in INES (contd.)(contd.)

Reduction in CDF with Passive Systems

Safety Considerations in INES Safety Considerations in INES (contd.)(contd.)

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Severe Accident Mitigation Approach in INESSevere Accident Mitigation Approach in INES

In-Vessel Retention of the Degraded Core

Preservation of the Containment Boundary

Minimization of the FP Release into the Environment

Injection of Emergency Coolantinto the Reactor Vessel External Reactor Vessel Cooling

Protect the Containment Basematfrom the Attack of Molten Corium

Maintain the Containment PressureBelow the Design Limit

Containment Spray

Reactor Cavity Flooding

Cavity Design Characteristics

Limit the Slow Pressure Increase

Prevent Rapid Pressure Increase

Containment Spray

Filtered Venting

Pressure Relief Valves

Hydrogen Control

Design to Prevent Other Rapid Scenarios

Retention of FPs inside Water Pool

Removal of FPs by Containment Spray Filtered Venting

Recommendation for Technology UsersRecommendation for Technology Users

Consider proven vs. futuristic sustainable designs for INES.

Select plant based on cost, grid requirement, site conditions, EIA studies, cooling water availability.

Select INES with best safety features: Even at increased cost.

Regulatory authority to be well equipped for licensing INES

HRD in project management; BIS; design & engineering; equipment design; installation & commissioning; O & M.

Sustainable front-end and back-end fuel supply

Life-time technical & safety support

Waste management schemes

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Hyperlinks in slides 36 Hyperlinks in slides 36 -- 40 40

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Economies with the highest share of nuclear power generation Economies with the highest share of nuclear power generation have high dependency on imported fuels.have high dependency on imported fuels.

Country Energy Import Dependency (%)

Nuclear Generation Share (%)

Korea 84 40

Japan 80 30

Chinese Taipei 89 21

USA 27 20

Environmental experts suggest that the contribution from fossil Environmental experts suggest that the contribution from fossil fuels to global energy should be limited to < 30% by 2050 to fuels to global energy should be limited to < 30% by 2050 to limit greenhouse gases to double the preindustrial levels.limit greenhouse gases to double the preindustrial levels.

Currently known sources that do not emit greenhouse gases, Currently known sources that do not emit greenhouse gases, such as nuclear energy and renewables would have to grow by such as nuclear energy and renewables would have to grow by a factor of about 15 from year 2000 levels for this to happen a factor of about 15 from year 2000 levels for this to happen or or by a factor of 50 if nuclear power is excludedby a factor of 50 if nuclear power is excluded..

Asia Pacific Energy Research Centre report “Nuclear power generation in the APEC region”, 2004

Challenges for Nuclear Power DevelopmentChallenges for Nuclear Power Development

NPPs have high capital cost:

—

Nuclear:

45–75% of total nuclear electricity cost

—

Coal plants: 25–60%

—

Gas plants:

15–40%

De-regulation of electricity markets: Protected purchases & Govt. guaranties difficult for nuclear power.

Alternative generating technologies are increasingly efficient, and their capital costs have fallen significantly.

Achieving economic competitiveness of future plants is a major goal.

Impact of TMI and Chernobyl events: -

In 1970s, NE was growing at 30%/yr

-

Limited to 15% in 1980s-

In some countries public opinion voted for phasing out of existing NPPs, due to concerns over safety

Chernobyl accident prompted management and safety improvements in NPPs. These safety enhancements resulted in very high availability factors by mid 1990s.

Achieving high levels of safety in new NPPs has been a major goal for IAEA & nuclear industry.

Simplified Plant ConceptSimplified Plant Concept

Passive Core Cooling SystemPassive Core Cooling System

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Passive Core Cooling SystemPassive Core Cooling System

45

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Containment isolationThis is provided to prevent or limit the escape of fission products that may result from postulated accidents. In the event of an accident, the containment isolation provisions are designed so that fluid lines penetrating the containment boundary are isolated.

Passive containment cooling system This consists of several components to effectively cool the containment in the unlikely event of an

accident so the design pressure is not exceeded, and the pressure is rapidly reduced. Natural circulation and water evaporation contribute to the cooling system.