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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
1
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.
2
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”
3
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.
8
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
.
9
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
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
14
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.
15
INES INES
and and
Technology User CountriesTechnology User Countries
Technology & Safety ApproachesTechnology & Safety Approaches
16
17
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 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
36
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
37
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.
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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.
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