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

Transcription

1 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.

2 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.

3 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.

4 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

5 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

6 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

7 Licensing Basis It depends on: Design bases & Design Basis Information Configuration management Design control through various means

8 Challenges in maintaining Design Basis Knowledge Ageing plant technology Plant modifications Application of new safety & operational requirements Possible human errors

9 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

10 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

11 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.

12 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)

13 Organisation set-up in India

14 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

15 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

16 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.

17 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.

18 Spectrum of DBI Informations - NPCIL The various DBI informations retained in the knowledge bank include the followings : - Buildings - Systems - Equipment - Nearby Installations Lateral Effects- Preoperational seismic walk throughs - Suggestions from Safety & Licensing reviews - Lessons learnt from operational experiences - Upgrades in the systems

19 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

20 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

21 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

22 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

23 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.

24 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

25 Finite Element Analysis of TSE

26 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.

27 Original Design New Design

28 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.

29 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

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31 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.

32 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.

33 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

34 Spent Fuel Pool

35 Flow chart for calculations

36 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

37 Temperature (C) Bhabha Atomic Research Centre, Mumbai Variation of temperature Water Temp Air Temp Days

38 Heat Loss (kw) Bhabha Atomic Research Centre, Mumbai 300 Variation of heat loss Qev Qrad Qcon days

39 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.

40 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

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43 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.

44 THANK YOU