Two Phase Natural Circulation Analysis of Passive Residual Heat Removal System

1. Young-Jong Chung* Korea Atomic Energy Research Institute Two Phase Natural Circulation Analysis of Passive Residual Heat Removal System Title is �Title is �

2. 2 CONTENTS INTRODUCTION SMART Plant and Characteristics VISTA Experimental Facility ANALYSIS CODE INITIAL and BOUNDARY CONDITIONS RESULTS and DISCUSSIONS CONCLUTIONS This slide is table of contents of my presentation First, I�d like to introduce SMART-p designThis slide is table of contents of my presentation First, I�d like to introduce SMART-p design

3. 3 INTRODUCTION SMART (System-integrated Modular Advanced ReacTor) : Integral type pressurized water reactor Maximum core power of 330 MWt Inherent safety characteristics & Passive safety systems In order to confirm the enhanced safety of SMART, systematic safety analyses have been performed : Total loss of flow (TLOF) Steam line break (SLB) Feedwater line break (FLB) Small break loss of coolant accidents (SBLOCA) In order to evaluate the safety and to optimize the design, probabilistic safety assessment (PSA) for the SMART basic design has been performed As you know from the previous lecture, SMART is the abbreviation of System-integrated Modular Advanced ReacTor. It is an integral type pressurized water reactor with a maximum core power of 330 MW thermal. Korea Atomic Energy Research Institute (KAERI) designed the SMART for seawater desalination and small-scale electricity generation. It aims to produce 40,000 m3/day of potable water using approximately 10% of the total energy produced and to generate about 90 MW of electricity using the remaining energy. Since the minimization of the radiation release to the environment is the key safety concern, it is required to enhance the safety. Therefore, several inherent safety design characteristics such as large negative moderator temperature coefficient , large volume of passive pressurizer are adopted. Inherent safety design enhance the resistance to a wide range of transients and accidents. For example, large negative moderator temperature coefficient provides the strong resistance to the power transients. In addition to these inherent safety design features, the passive safety systems such as the Passive Residual Heat Removal System (PRHRS), Emergency Core Cooling System (ECCS) are also adopted. Passive system means that it is operated by natural phenomena such as the gravity ,gas pressure or battery power without the electrical power. Passive system has the high reliability in its operation. ing and advanced passive design features The total loss of flow is the limiting accident decreasing the reactor coolant flow rate.As you know from the previous lecture, SMART is the abbreviation of System-integrated Modular Advanced ReacTor. It is an integral type pressurized water reactor with a maximum core power of 330 MW thermal. Korea Atomic Energy Research Institute (KAERI) designed the SMART for seawater desalination and small-scale electricity generation. It aims to produce 40,000 m3/day of potable water using approximately 10% of the total energy produced and to generate about 90 MW of electricity using the remaining energy. Since the minimization of the radiation release to the environment is the key safety concern, it is required to enhance the safety. Therefore, several inherent safety design characteristics such as large negative moderator temperature coefficient , large volume of passive pressurizer are adopted. Inherent safety design enhance the resistance to a wide range of transients and accidents. For example, large negative moderator temperature coefficient provides the strong resistance to the power transients. In addition to these inherent safety design features, the passive safety systems such as the Passive Residual Heat Removal System (PRHRS), Emergency Core Cooling System (ECCS) are also adopted. Passive system means that it is operated by natural phenomena such as the gravity ,gas pressure or battery power without the electrical power. Passive system has the high reliability in its operation. ing and advanced passive design features The total loss of flow is the limiting accident decreasing the reactor coolant flow rate.

4. 4 INHERENT SAFETY CHARACTERISTICS The integral arrangement Eliminates the possibility of LBLOCA. Canned motor MCPs Eliminates MCP seal leak SBLOCA SGs location Maintains natural circulation up to the 25% power Helical coiled steam generator A large volume of passive PZR The system pressure is self-controlled using N2 gas Soluble boron-free operation with the low core power density Large negative MTC Now, I�ll explain the inherent safety deign characteristics in more detail. As you see in this figure, The reactor assembly of SMART contains major primary components such as a core, twelve Steam Generators (SGs), a Pressurizer (PZR), four Main Coolant Pumps (MCPs), and forty-nine Control Element Drive Mechanisms (CEDM) in a single PRV. The integral arrangement of the primary system removes the large size pipe connections between the major components, and thus fundamentally eliminates the possibility of Large Break Loss Of Coolant Accident. Large Break Loss Of Coolant Accident is the most severe design basis accident in the loop type pressurized water reactor, but we don�t worry about LBLOCA. Now, I�ll explain the inherent safety deign characteristics in more detail. As you see in this figure, The reactor assembly of SMART contains major primary components such as a core, twelve Steam Generators (SGs), a Pressurizer (PZR), four Main Coolant Pumps (MCPs), and forty-nine Control Element Drive Mechanisms (CEDM) in a single PRV. The integral arrangement of the primary system removes the large size pipe connections between the major components, and thus fundamentally eliminates the possibility of Large Break Loss Of Coolant Accident. Large Break Loss Of Coolant Accident is the most severe design basis accident in the loop type pressurized water reactor, but we don�t worry about LBLOCA.

5. 5 INTRODUCTION SAFETY SYSTEM Passive residual heat removal system Emergency core cooling system Over pressure protection system (POSRV) Shutdown cooling system Component cooling water system

6. 6 INTRODUCTION

7. 7 INTRODUCTION

8. 8 INTRODUCTION � VISTA Facility VISTA DESIGN Test facility to simulate the integral type reactor Scale ratio with respect to the reference plant 1/1 for height scale 1/96 for volume scale Major components Vessel : Height-4.0m, Diameter-0.17m 1 SG cassette, 1 MCP 1 train of PRHRS Primary components are simplified to be a loop type in order to perform easily maintenance and instrumentation Understand the thermal hydraulic responses for the integral type reactor

9. 9 PRHRS connect to Feedwater and steam linesPRHRS connect to Feedwater and steam lines

10. 10 ANALYSIS MODEL MARS 3.0 code 1-D and 3-D system analysis code for thermal hydraulic analysis of the light water reactor transients Developed at the KAERI by consolidating and restructuring the RELAP5/MOD3.2 and COBRA-TF codes SMART specific models Helically coiled SG Pressurizer with non-condensable gas Performed verification and validation using Comparison of RELAP5/MOD3 results Data of VISTA experiment T/H in the PRHRS is analyzed using TASS/SMR code.T/H in the PRHRS is analyzed using TASS/SMR code.

11. 11 ANALYSIS MODEL Heat transfer model for helical SG For tube side of helically coil�(Mori-Nakayama) For shell side of helically coil (Zukauskas) For nucleate boiling (Chen) For natural convection (Churchill-Chu)

12. 12 ANALYSIS MODEL

13. 13 ANALYSIS MODEL The secondary system has four identical sections. Each section consist of isolation valve, check valve, subsection pipe The secondary system has four identical sections. Each section consist of isolation valve, check valve, subsection pipe

14. 14 ANALYSIS MODEL The secondary system has four identical sections. Each section consist of isolation valve, check valve, subsection pipe The secondary system has four identical sections. Each section consist of isolation valve, check valve, subsection pipe

15. 15 ANALYSIS MODEL

16. 16 INITIAL/BOUNDARY CONDITIONS This initial value does not influence the steady state condition because the flow rate is �0�This initial value does not influence the steady state condition because the flow rate is �0�

17. 17 INITIAL/BOUNDARY CONDITIONS

18. 18 Event Description Initiating Event: Full power Loss of power occurs at 140.0 sec Opening the PRHRS valves and closing the MFIV/MSIV at 140.0 sec General Phenomena When the electric power is lost, MCP begins to coast-down ? decrease primary and secondary flow rate ? formed natural circulation ? decrease average pressure and temp. in the primary and secondary ? stabilize primary and secondary systems PZR water level decrease and end and intermediate cavities are empty Latent heat removes thru the natural circulation of primary and PRHRS Then, system temperature/pressure/level become to stabilize

19. 19 RESULTS and DISCUSSIONS-Experiment

20. 20 RESULTS and DISCUSSIONS The initial condition is one of the important parameters affecting the CHFR. The initial condition is one of the important parameters affecting the CHFR.

21. 21 RESULTS and DISCUSSIONS The initial condition is one of the important parameters affecting the CHFR. The initial condition is one of the important parameters affecting the CHFR.

22. 22 RESULTS and DISCUSSIONS MFIV/MSIV valve delay time, valve stroking timeMFIV/MSIV valve delay time, valve stroking time

23. 23 RESULTS and DISCUSSIONS

24. 24 RESULTS and DISCUSSIONS

25. 25 RESULTS and DISCUSSIONS Parametric Study � Do not model wall heat structure

26. 26 RESULTS and DISCUSSIONS Parametric Study � Chilled water supply or not in the ECT

27. 27 SUMMARY The realistic calculations for the natural circulation of the VISTA facility is performed to find thermal hydraulic characteristics in the PRHRS and capability of the MARS code to predict single-, two-phase natural circulation The PRHRS accomplishes well its functions in removing the transferred heat from the primary side in the SG as long as the Hx is submerged the water in the ECT. Natural circulation of the VISTA facility depend on Latent heat in the reactor vessel Friction and form loss of the geometry Heat transfer at the SG and the heat exchanger Result of MARS code calculation Calculate reasonably the natural circulation flow rate Under-predicts heat transfer at the SG and the heat exchanger Over-predicts the primary SG outlet temperature Over-predicts the heat exchanger outlet temprature Appears a periodic oscillation during the two phase natural circulation

28. 28 SUMMARY Find from this study Natural circulation flow rate is around 10% of the initial flow for the integral reactor The local boiling is occurred at the top of the heat exchanger Dominant heat transfer is boiling and condensation for the steam generator and heat exchanger under natural circulation condition, respectively Accurate model of the heat loss and heat capacity for the primary system is important for the natural circulation