Collaborative Project Proposal on Advanced Water Cooled Reactors (IND3)

1. Collaborative Project ProposalonAdvanced Water Cooled Reactors(IND3) R.K. Sinha Director, Reactor Design & Development Group Design Manufacturing & Automation Group Bhabha Atomic Research Centre, Mumbai, India

2. Need for the proposal • The growing intent to enhance the safety and economic - competitiveness of nuclear power plants has led to the design and development of several advanced water cooled reactors. • Many of these reactor systems intend to use innovative features like • Natural circulation for core heat removal • Large pools to serve as heat sinks • High performance annular fuel rods • In bundle injection during LOCA etc. • Several phenomena associated with these features are required to be investigated extensively over a wide range of operating conditions. • The theoretical models developed for predicting the performance of such systems also need to be validated.

3. Objectives • Experimental and analytical investigations on steady state and stability performance of both single-phase and two-phase natural circulation reactor systems. • Studies on supercritical fluid as coolant, for use in supercritical reactors. • Studies on the flow pattern void profile and temperature profile, in a fuel bundle under direct in-bundle Emergency coolant injection. • Experimental and theoretical studies on mixing and stratification in large water pools. • Investigations on reliability of passive systems. • Studies on various thermal-hydraulics aspects of annular fuel rods and their thermal margin under normal and oscillatory conditions.

4. Issues related to Advanced Water Cooled Reactors (1/4)

5. Issues related to Advanced Water Cooled Reactors (2/4)

6. Issues related to Advanced Water Cooled Reactors (3/4)

7. Issues related to Advanced Water Cooled Reactors (4/4)

8. Funding • Each country is expected to meet its own expenses including those on manpower deployed for this purpose • The flow of information should be done by e-correspondence, hence avoiding the expenses incurred in travel • Where meetings are essential, India will offer to organise them at Mumbai

9. Resources • India is developing many innovative and advanced reactor systems like Advanced Heavy Water Reactor (AHWR), Compact High Temperature Reactor and Supercritical Water Cooled Reactor. • A number of facilities to study various phenomena related to above reactor systems have been set up. • High Pressure Natural Circulation Loop • Integral Test Loop • Flow Pattern Transition Instability Loop • Parallel Channel Loop • Instability Demonstration Facility • Super Critical Natural Circulation Loop being set-up • Facility for Integral System Behaviour Experiments

10. Content and workplan (1/2) • Exact work plan shall be worked out based on discussions with other interested member states. • Proposed implementation process is shown in below • First Year • Phase-0 (Pre project stage) • Formulation of scope, schedule and responsibilities for the entire project duration • Approval at institutional levels • Approval of detailed structure of activities and detailed responsibilities through e-correspondences • Monthly exchange of newsletters giving information of status • Phase-1 • E-correspondence and exchange of initial responses • Review meeting to exchange views and midcourse course corrections if any

11. Content and workplan (2/2) • Second Year • Phase-2 • Further activities by MS at their respective workplaces • E-correspondence and exchange of results • Review meeting to exchange views and midcourse course corrections if any • Preparation of related documents • Third Year • Phase-3 • Compilation of results • Preparation of related documents • In IAEA INPRO secretariat nominates one person to coordinate the work among all member states

12. Expected outcome and deliverables • Enhanced knowledge base on performance of INS and validation of analytical tools for predicting performance of such systems. • Substantial database on stable and unstable two-phase natural circulation, void fraction measurement (using various intrusive and non-intrusive techniques) and flow pattern transition is expected to be generated from the experimental facility. In addition data on the in-bundle injection of ECCS coolant will be generated to establish its adequacy. • Steady state and stability behavior data will be generated which can be used for model validation and better understanding of the heat transfer phenomena with supercritical water loop. • Experimental data generation in water pools, data analysis and comparison of experimental data with analytical prediction will be carried out for improved understanding of the thermal stratification phenomenon. • Investigations on reliability estimation of passive systems for reactor safety and heat removal will be carried out. • Investigation on thermal hydraulic studies related to annular fuel will be carried out.

13. Procedure for implementation • It is anticipated that extra budgetary CRP would be an appropriate mechanism of implementation.

14. Interface with other similar projects inside or outside the agency • Currently lndia is participating in the IAEA CRP on "Natural Circulation Phenomena, Modeling And Reliability of Passive Systems that utilize Natural Circulation". A selected list of documents referred by us is given below: • Natural Circulation in Water Cooled Nuclear Power Plants Phenomena, Models and Methodology for System Reliability Assessments, IAEA-TECDOC-I474, 2005, Date of Issue: 8 December 2005. • Innovative Small and Medium Sized Reactors: Design Features, Safety Approaches and R&D Trends, IAEA-TECDOC-145 I, 2005, Date of Issue: 9 June 2005. • Innovative Small and Medium Sized Reactor Designs 2005,: Reactor with Conventional Refueling Schemes, IAEA-TECDOC-1485, 2005, May, 2005. • Technical Feasibility and Reliability of Passive Safety Systems for Nuclear Power Plants, lAEA-TECDOC- 920,1996, Date of Issue: 16 December 1996.

15. Status of current activities in India

16. Experimental and analytical investigations on steady state and stability performance of natural circulation reactor systems

17. Integral Test Loop (ITL): Simulates the MHT, safety and control systems of AHWR IC SD JC SB AA GDWP SFP PBC QOV HEADER FCS Isometric of ITL BFST • Major Design Parameters • Pressure : 10 MPa • Temperature : 315 C • Elevation : 1:1 • Volume scaling : 1:452 • Objectives • Natural circulation performance during start-up, power raising and normal operation • Simulation of LOCA & non-LOCA transients • Performance evaluation of isolation condenser the advanced accumulator and the GDCS

18. ITL: NC Performance Steady state performance Steady state flow rates are within 15% of RELAP5 predictions Stability Performance The stable and unstable experimental data are well characterised by TINFLO-S.

19. ITL: Cold Start-up Simulation Pre-test RELAP5 simulation neglecting heat losses ITL Data Simulation of cold start-up at 2% FP and 10 bar General trends are similar. However, ITL takes about one day where as RELAP5 simulation takes only half a day

20. Flow Pattern Transition Instability Loop (FPTIL) • Objectives: Generation of data for • Bubbly flow to slug flow transition, • Slug flow to annular flow transition, • Void fraction • Flow pattern specific pressure drop • Steady state two-phase NC • Stability and • Start-up • Design conditions • Pressure : 125 bar • Temperature : 315 C • Test sections : 7, 9.1, 15.75 and 20 mm

21. Features of FPTIL Typical observed flow pattern Comparison of measurements of void fraction • Void fraction measurement by neutron attenuation technique developed at HPPD and conductance probe developed at RED. NRG also enabled visualization of high pressure two-phase flow FPTIL installed in Apsara RH

22. FPTIL: Comparison with theory Prediction with Ishii correlation Comparison of measured flow rate with RELAP5/MOD3.2 predictions

23. FPTIL: Experimental Stability Map Both type-I and type-II instabilities are observed in FPTIL

24. FPTIL: Effect of pressure on Type-I instability Type-1 Instability disappears at higher pressure

25. High Pressure Natural Circulation Loop (HPNCL) Sub cooler Test Section Bus Bar • Objectives • To study steady state and stability behaviour • Validation of computer codes • To test the start up procedure of a boiling natural circulation loop • Major Design Parameters • Design Pressure : 114 kg/cm2 • Design temperature : 315 oC • Maximum Power : 80 kW • Loop Diameter : 50 mm • Elevation : 3000 mm • Heated Section : 1000 mm Schematic of High Pressure Natural Circulation Loop

26. HPNCL: Steady State and Start-Up Experimental Results Mass Flow rate (kg/s) Theoretical Experimental data Test Section power (kW) Pressure (bar) Natural Circulation Characteristics simulated by RELAP5 code. Effect of pressure on the natural circulation flow behavior

27. HPNCL: Stability Performance Stability map for HPNCL at low pressure

28. Parallel channel instability studies Steam line Steam Drum Feed water line Riser Riser Header Heater Feeder • Parallel Channel Loop • Design Pressure : 20bar  • Design Temperature: 215 C  • Number of channels: 4  • Max. power per channel: 50kW • Height of loop: 3.5 m • Heater: Vertical tube Ǿ10mm x 800mm long –direct electrically heated  • Steam Drum: Horizontal 300NB x 0.8 m long with internals like baffle plate and feed water sparger  • Riser & Feeders: Pipes 25NBxSch40

29. Parallel channel instability studies Objectives: Behaviour of unequally heated parallel channels under natural circulation Parallel channel instability Void reactivity feedback simulation Special features: Void fraction measurement in heaters and risers using conductance probes Provision for transparent pipe modules in risers for flow pattern visualization at low pressures Instrumented test section to detect CHF occurrence A typical instability result using RELAP5/Mod3.2 simulation

30. Studies on supercritical fluid as coolant

31. Natural Circulation with SCW • Large variation in thermal expansion coefficient near the critical point of supercritical water can be exploited for designing NC based SCWRs. • It is essential to identify the operating parameters near the critical point such that high circulation rate and hence high heat transfer rates are achievable during natural circulation for the design of such reactors. • In addition, it is desirable to operate such loops in a stable condition, which requires identification of the stable and unstable zone by a stability analysis. • In view of this it is proposed to set-up a supercritical natural circulation water loop (Design Pressure: 25 MPa, Design Temperature 450 C).

32. Supercritical Water Loop • OBJECTIVES • Generation of database for • Stability performance • Steady state performance • Pressure drop • Heat transfer coefficient • Critical flow

33. Natural Circulation with SCW • A computer code for steady state and linear stability analysis of SCW- NCL has been developed and benchmarked. • The code has been used to carry out the steady state and linear stability analysis of a proposed SCW-NCR. Steady state mass flow rate with power for proposed SCW-NCL

34. Instability Demonstration Facility • Objectives: • To validate theoretical models and computer codes developed for steady state and stability analysis. Comparison of steady state data with theory

35. Comparison of steady state data with theory • New findings • A conditionally stable regime is observed where stable or unstable flow can prevail depending on the operating procedure. Observed phase space for various powers

36. Studies on flow pattern void profile and temperature profile in a fuel bundle under direct in-bundle emergency coolant injection

37. In-bundle injection and heat transfer studies Intensifier Frame Grabber Mirror CCD Camera Scintillator Video Monitor PC/AT Object Computer VTR Typical slug flow pattern Obtained by Neutron Radiography (APSARA experiments) Schematic of Neutron Imaging System • Visualisation of flow during high pressure in-bundle injection of ECCS flow. • Generation of flow pattern transition data and flow pattern specific pressure drop data. • Void fraction measurement by Neutron radiography, Capacitance conductance probes. • Study of flow pattern transition instabilities in two-phase natural circulation

38. Schematic of the Experimental Facility

39. Experimental and theoretical studies on mixing and stratification in large water pools

40. Thermal stratification in large water pools • Thermal stratification in large pools with immersed heat exchangers is relevant for passive decay heat removal systems in many advanced reactors • Numerical analysis of thermal stratification using 1/8th sector of GDWP with isolation condensers (IC) carried out using PHOENICS • Temperature field predictions after 6 hours show predominant stratification in IC pool Simulated Isolation Condenser in ITL Temperature Contour after 6 hours of IC operation

41. Investigations on reliability of passive systems

42. Studies on Reliability of Passive Systems Failure Success • Failure criteria for natural circulation in AHWR for nominal operating conditions are identified. • Deviation of Parameters considered which may cause failure are • Pressure, Power, Subcooling and SD level • Failure points are predicted using the code RELAP5/MOD3.2 • Failure surface/ Response surface is generated from the loci of such failure data points. • Failure frequency has been calculated from the classical fault tree analysis. Failure surface for Natural Circulation Failure frequency of Natural Circulation

43. Studies on thermal-hydraulic aspects of annular fuel

44. Development of Annular Fuel • The annular fuel rod provide cooling on the outside surface and inside surface of the fuel. • Advantages of Annular Fuel • Increases both safety margins as well as core power density. • Very low operating peak fuel centerline temperature. Small fission gas release due to low temperature and reduction of pellet cracking due to low temperature gradient. • Small cladding temperature rise in a LOCA due to limited stored energy in the fuel. • It can be used in AHWR as well as PHWR for power up-rating. Radial temperature profile of Solid and Annular fuel at the hot spot A typical annular fuel cluster (45 pins) Temperature profile of a typical annular fuel cluster (Preliminary results using the computer code being developed )