Design Basis Provisions for New and Existing Nuclear Power Plants

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  • Design Basis Provisions for New and Existing Nuclear Power Plants and Nuclear Fuel Cycle Facilities in India

    R. S. Soni Head, Technology Development Division, Bhabha Atomic Research Centre, Mumbai, India.

  • INTRODUCTION

    India has 3-Stage Nuclear Power Program.

    Various facilities under design, construction or operation.

    Design Basis Knowledge Management (DBKM) is an important and challenging task.

    Design Basis Knowledge contributes towards: -

    Safe operation of running plants

    Design and construction of new facilities

    Addresses issues related to future decommissioning activities.

    Bhabha Atomic Research Centre, Mumbai

  • OBJECTIVE OF DBKM

    To ensure that the accurate information consistent with the physical and operational characteristics of the nuclear power plants and nuclear fuel cycle facilities is available in a timely manner for making safe, knowledgeable and cost effective decisions with confidence.

    Bhabha Atomic Research Centre, Mumbai

  • Design basis knowledge is obtained from

    Evolving new technologies and research findings.

    Feedback from operational experience, both national and international.

    Evolving regulatory requirements.

    Design Basis Information

    It acts as a foundation of information for safe design, operation, maintenance, testing, commissioning and de-commissioning of the facility

    Bhabha Atomic Research Centre, Mumbai

  • Design Basis Information

    It essentially includes:

    Design Requirements

    Design Basis

    Design Requirements

    Form and Function of SSC

    Capabilities and Capacities

    Physical sizes and Dimensions

    Limits and Set points

    Bhabha Atomic Research Centre, Mumbai

  • Design Basis

    Safety classification w.r.t. hazard potential.

    Specification, Criteria, Safety function of SSC

    Codes & Standards

    Qualifications, Design Calculations

    Transverse effects on other SSCs

    Safety margins in the design

    Accident & Fault scenario analysis

    Environmental considerations & its impacts

    Bhabha Atomic Research Centre, Mumbai

  • Licensing Basis

    It depends on:

    Design bases & Design Basis Information

    Configuration management

    Design control through various means

    Bhabha Atomic Research Centre, Mumbai

  • Challenges in maintaining Design Basis Knowledge

    Ageing plant technology

    Plant modifications

    Application of new safety & operational requirements

    Possible human errors

    Bhabha Atomic Research Centre, Mumbai

  • Ideal Design Basis Program shall have:

    Documented reference for use in design process & future plant modification

    Serve as basis for technical & safety reviews, etc.

    Documented reference to support continued operations

    Serve as a basis for licensing of the facility

    Support the review of technical specification changes

    Bhabha Atomic Research Centre, Mumbai

  • An ideal Design Basis Program should help in reducing the likely hood of inadvertent plant operations outside the design basis

    Any Design Change / Modification

    System engineer Key role in coordination

    Design, implementation, final testing and commissioning

    Independent review of design changes

    Approval from safety & licensing body

    Bhabha Atomic Research Centre, Mumbai

  • The potential impact of not having an appropriate DBKM system is the loss of ability to perform safety related functions when really required.

    In addition, un-availability of right information at right time in right format to engineering and operations staff can lead to human errors having potential safety consequences.

    Bhabha Atomic Research Centre, Mumbai

  • Management of Design Basis Information in India

    Access to plant design information

    Original Design Basis Information is vital.

    NPPs are designed, constructed and operated by a single agency NPCIL.

    Private contractors and consultants are hired only for their general services.

    Full access to plant design basis information to owner and operator (Unlike turn-key projects)

    Bhabha Atomic Research Centre, Mumbai

  • Organisation set-up in India

    Bhabha Atomic Research Centre, Mumbai

  • Safety assessment

    Atomic Energy Regulatory Board (AERB) has a legal authority to perform safety and regulatory functions.

    Safety assessment program

    - To improve plant safety

    - To facilitate immediate knowledge transfer

    - To bring out any latent weaknesses early

    - To take quick corrective actions

    India follows multi level safety review program

    Bhabha Atomic Research Centre, Mumbai

  • Committees of AERB

    Unit Safety Committee (USC)

    Safety Review Committee for Operating Plants (SARCOP)

    Board of AERB

    Internal Committees of NPCIL

    Station Operation Review Committee (SORC) at site

    Safety Review Committee (SRC) at head quarters

    Bhabha Atomic Research Centre, Mumbai

  • Operational Experiences

    A well structured practice to learn lessons from operational experiences (Nationally & Internationally)

    Emphasis on Prompt Operational Experience Feedback

    Important information is compiled at headquarters and flash reports are issued to all stations

    Care to prevent recurrence of any untoward event.

    Bhabha Atomic Research Centre, Mumbai

  • Operational Experiences (continued)

    Generation of OPEX (Operation Experience Feedback) reports

    At Station Level, OERC (Operation Experience Review Committee) reviews Operation Experience Feedback from

    - Other stations

    - IAEA, WANO, COG and other such agencies, and, identifies actions to be taken.

    The identified actions are further reviewed in Station Operation Review Committee before implementation.

    Bhabha Atomic Research Centre, Mumbai

  • Spectrum of DBI Informations - NPCIL

    The various DBI informations retained in the knowledge bank include the followings :

    - Buildings

    - Systems

    - Equipment

    - Nearby Installations Lateral Effects- Pre-operational seismic walk throughs

    - Suggestions from Safety & Licensing reviews

    - Lessons learnt from operational experiences

    - Upgrades in the systems

    Bhabha Atomic Research Centre, Mumbai

  • Evaluation of existing facilities

    Valuable information is available from the existing facilities which have been operating for years.

    Learning from operating plants an essential part of design basis knowledge management.

    Any un-available or partially available information needs to be generated starting with the most critical system first.

    Field visits to ascertain physical installation details of SSCs

    Bhabha Atomic Research Centre, Mumbai

  • Evaluation of existing facilities Three main areas needs to be addressed: 1. Physical configuration - piping & equipment layout, P&IDs - As built drawings, maintenance aspects

    2. Design requirements - Functional & safety requirements - Design calculations & their adequacy - Safety analysis

    3. Facility configuration - Up to date design information - Design change information - Operational configuration - Surveillance & testing, training, - Procurements & NDT documents

    Bhabha Atomic Research Centre, Mumbai

  • Evaluation of existing facilities

    Difficulties faced due to

    Non-availability of full documentation related to their design

    Non-availability of main design principles

    Non-availability of information related to plant modifications and its cumulative effects

    Sketchy information about plant maintenance history

    Bhabha Atomic Research Centre, Mumbai

  • Knowledge from In-service Inspection

    Involves periodic examination of components of NPP during its lifetime.

    Determines the health of components.

    Provides access to critical information on influences which depend on time and operating history

    - stress, temperature, irradiation, corrosion attack, vibration, fretting, etc.

    Non-destructive examination provides valuable inputs about flaw characteristics and degradation of material properties

    Bhabha Atomic Research Centre, Mumbai

  • Learning From Failures

    Frequent failures should be investigated

    Enhances design basis knowledge

    E.g. Thermo Siphon Evaporator (TSE)

    TSE is used for volume reduction of the product

    Plants were witnessing regular shutdowns due to TSE failure

    Task force was formulated to investigate the root cause.

    Detailed study was carried out.

    Bhabha Atomic Research Centre, Mumbai

  • Major problems observed in TSE

    High Thermal Stresses

    Differential thermal expansion between tube and shell results in:

    High axial tube thermal forces (~ 6 to 8 Te)

    High thermal stresses in TTS weld joints

    Corrosion

    Highly corrosive environment: Nitric acid service at boiling temperature

    Inter-granular Corrosion (IGC)

    Crevice Corrosion

    Bhabha Atomic Research Centre, Mumbai

  • Finite Element Analysis of TSE

  • Design modifications for TSE

    Use of material with better IGC rate: SS 304L (Refined)

    Expansion bellow on shell to reduce the thermal stresses in tube, tube sheet and TTS joints (tube load reduces by a factor of 18 to 20)

    Improvements in TTS joint

    - Full strength welded joint

    - Light expansion to close the crevice between tube & tube-sheet to avoid crevice corrosion.

    Bhabha Atomic Research Centre, Mumbai

  • Original Design New Design

  • Changing Regulatory Requirements

    Regulatory requirements changes due to new findings.

    Sometimes these requirements have a bearing on existing plants.

    Such occasions are rare but subsequent procedures are exhaustive.

    However, it provides lot of information on actual strength, actual loadings, safety margins, etc.

    Such information is precious and contributes to design basis knowledge.

    Bhabha Atomic Research Centre, Mumbai

  • E.g. Seismic Requalification for new loads

    Nuclear facility building located at Kalpakkam, India

    Originally designed for earthquake PGA of 0.06g.

    Latest guidelines require building to qualify for an earthquake with a PGA of 0.078g.

    Seismic requalification was carried out.

    Generated lot of information

    Bhabha Atomic Research Centre, Mumbai

  • Determination of actual loads

    (Design loads > 20 % of actual loads)

    Probabilistic approach (seismic fragility method)

    This involved seismic margin study and evaluation of HCLPF (High Confidence Low Probability of Failure) capacity of the building.

    The HCLPF capacity

    0.41g for columns

    0.24g for beams

    Building is safe for new seismic loads.

    Bhabha Atomic Research Centre, Mumbai

  • Learning From Accidents

    Accidents like Fukushima incident teach us very important lessons.

    Open new chapters and challenges for the designers.

    Significant for Design Basis Knowledge

    In India, safety review of all the spent fuel storage bays was carried out post Fukushima incident to analyse the impact of station blackout.

    Bhabha Atomic Research Centre, Mumbai

  • E.g. Detailed study of Spent Fuel Pool at Tarapur, India

    Station Black Out - No Class IV and Class III power supply

    Non availability of important normal operation systems (polishing system, cooling system and ventilation system)

    Rise in pool water temperature due to decay heat from spent fuel bundles.

    Critical response parameters:

    Time required for water to start boiling

    Time required for loss of water shielding

    Bhabha Atomic Research Centre, Mumbai

  • Spent Fuel Pool

    Bhabha Atomic Research Centre, Mumbai

  • Flow chart for calculations

    Bhabha Atomic Research Centre, Mumbai

  • Spent Fuel Storage Pool (Tarapur) Capacity: To store 1200 tons of heavy material Heat load = 423 kW Time required for water to start boiling = 21 days Time required for loss of water shielding = 100 days

    Bhabha Atomic Research Centre, Mumbai

  • Variation of temperature

    0

    20

    40

    60

    80

    100

    120

    0 5 10 15 20 25 30 35 40

    Days

    Tem

    pera

    ture

    (C

    )

    Water Temp

    Air Temp

    Bhabha Atomic Research Centre, Mumbai

  • Variation of heat loss

    Bhabha Atomic Research Centre, Mumbai

    0

    50

    100

    150

    200

    250

    300

    0 5 10 15 20 25 30 35 40

    days

    Heat

    Lo

    ss (

    kW

    )

    Qev

    Qrad

    Qcon

  • Pre-operational seismic walk through

    In India, it is practice to conduct pre-operational seismic walk-through.

    To ensure the installation of various seismic supports as per design intent

    To identify the areas with in-adequate supports.

    To identify the interaction concerns between the systems of various safety classes

    To locate various undesired loose, untied / unanchored components, tools, etc. used during the construction activity.

    Bhabha Atomic Research Centre, Mumbai

  • A detailed procedure for the pre-operational seismic walk-through of the NPPs exists.

    Feedback should form an important element of design basis knowledge management program

    Kaiga-1 plant 500 observations

    RAPP-3 plant 270 observations

    Bhabha Atomic Research Centre, Mumbai

  • Conclusion

    Vast resource of knowledge is available nationally and internationally.

    Knowledge should reach right people at right time for its effective implementation in nuclear safety.

    Effective Deign Basis Knowledge Management System is essential.

    DBKM system strongly influences design provisions for new and existing NPPs & NFCFs.

    Bhabha Atomic Research Centre, Mumbai

  • THANK YOU

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