Evaluation of Two Phase Natural Circulation Flow in the Reactor Cavity under IVR-ERVC for Different Thermal Power Reactors

Transcription

1 Evaluation of Two Phase Natural Circulation Flow in the Reactor Cavity under IVR-ERVC for Different Thermal Power Reactors Rae-Joon Park, Kwang-Soon Ha, Hwan-Yeol Kim Severe Accident & PHWR Safety Research Division Korea Atomic Energy Research Institute

2 CONTENTS Introduction IVR-ERVC Concept Research Needs & Backgrounds Objectives RELAP5 Input Model RELAP5 Results & Discussion Conclusions 2

3 Introduction (1) In-Vessel corium Retention through External Reactor Vessel Cooling Design Feature for SA Mitigation AP600 & AP1000 in USA Loviisa in Finland KERENA in Germany, and so on As a part of SAMG Strategies APR1400 & OPR1000 in Korea Current Operating Plants, and so on Schematic Diagram of IVR-ERVC 3

4 M M M M M M M M M M Introduction (2) IVR-ERVC The strategy of the APR1400 for severe accident mitigation aims at retaining molten core in-vessel first and ex-vessel cooling of corium second in case the reactor vessel fails, reinforcing the principle of defense-in-depth. IVR-ERVC was adopted as one of severe accident management strategies. In IVR-ERVC condition, the cavity will be flooded from IRWST by the SCP and the BAMP to the hot leg penetration bottom level. Containment Building Aux. Building Steam Generator Steam Generator IVR-ERVC in the APR1400 : Active system (Not passive) & non severe accident design feature RCS CVCS BAMP (200 gpm) SCP (5000 gpm) IRWST External Reactor Vessel Cooling System Reactor Vessel Cavity HVT Reactor Cavity Flooding System IRWST Schematic Diagram of the APR1400(Advanced Power Reactor) 4

5 CHF [MW/m 2 ] Introduction (3) To evaluate IVR-ERVC Thermal load Heat removal rate (CHF) Success Criteria CHF > Thermal Load In general, an increase in natural circulation coolant mass flow rate in cooling channel leads to increase in the heat removal rate at the reactor vessel wall. To Increase natural circulation flow rate Gap configuration to form streamline flow Optimal coolant inlet/outlet design Steam venting to prevent pressure buildup in annular gap between reactor vessel and insulation Thermal Loading - Accident Sequence - Melt Configuration - Melt Composition Cooling Water Circulation Features Wall CHF - Geometry - Flow Condition SULTAN Experimental Results on CHF in CEA/France Q = 20 MW Subcooling 70 o C Saturated Cond. s = 5 cm s = 10 cm s = 15 cm Natural circulation flow feature should be evaluated Mass Flow Rate [kg/sec] 5

6 Introduction (4) Design features of OPR1000 and APR1400 Design Parameters OPR1000 APR1400 Core Thermal Power (MW) Fuel(UO 2 ) Mass (ton) Mass for Active Core Zircaloy-4 (ton) Bottom Head Inner Diameter (m) Bottom Head Thickness (cm) Number of ICI Nozzle in the Lower Head To enhance heat removal rate(increase natural circulation flow) APR1400 : Optimal insulation design OPR1000: Not yet 6

7 Introduction (5) Objective: Analysis of two phase natural circulation mass flow rate in the annular gap between the outer reactor vessel wall and the insulation using the RELAP5/MOD3 Contents To analyze the coolant circulation coolant mass flow rate in APR1400 & OPR1000 To analyze the effects of the coolant injection temperature and water level on the coolant mass flow rate 7

8 RELAP5 Input Model (1) RELAP5/MOD3 This system thermal hydraulic computer code was developed at the INL(Idaho National Laboratory) for the USNRC. This 1-D best estimate transient simulation computer code uses six equations on mass, momentum, and energy equations. This computer code includes analyses required to support rulemaking, licensing audit calculations, evaluations of accident mitigation strategies, evaluations of operator guidelines, and experiment planning analyses. This computer code can be used for the simulation of a wide variety of hydraulic and thermal transients in both nuclear and non-nuclear systems involving mixtures of steam, water, noncondensable, and solute. 8

9 RELAP5 Input Model (2) Ht St ,24 Ht St ,22 Ht St ,20 SV 92 SJ 91 Annulus 90(2) SJ 81 Annulus 80(2) SJ 71 Annulus 70(10) SJ 93 TDV 104 SJ 103 No. Heat Structure 100 Heat Structure 200 Single Volume 20 Annulus 30, 40,50 Description Spherical Reactor Vessel Cylindrical Reactor Vessel Volume Between the Reactor Vessel Bottom and the Insulation Volume Between the Spherical Reactor Vessel and Insulation Ht St 200-1,10 Ht St ,25 Ht St , ,17 SJ 61 Annulus 60 (10) SJ 51 Annulus 50 (5) SJ 41 Annulus 40-7, ,7 SJ 63 Annulus 100 (50 Vols, Cavity Volume) TDJ 105 TDV 106 Annulus 60,70, 80, 90 Single Volume 92 Annulus 100 Single Volume 10 Volume Between the Cylindrical Reactor Vessel and Insulation Reactor Vessel Outside Cavity Volume Bottom Side Cavity Volume ,13 Ht St 100-9, ,3 SJ 31 Annulus 30-9,10 Single Volume 15 Bottom Cavity Volume under the Reactor Vessel 100-7, , ,4 30-7,8 30-5,6 30-3,4 Time Dep. Volume 104 Time Dep. Volume 106 Containment Atmosphere Water Source (CFST) 100-1,2 30-1,2 SJ 21 Single Junction 16 Water Inlet SV 20 SJ 16 SV 15 SJ 11 SJ 111 SV 10 Single Junction 63 Single Junction 93 Water Outlet Steam Outlet 9

10 RELAP5 Input Model (3) Insulation design for natural circulation flow Input Conditions OPR1000 (Assumed) APR1400 Water Inlet Area (m 2 ) Water Outlet Area (m 2 ) Steam Outlet Area (m 2 ) Water Outlet Position from the Reactor Vessel Bottom (m) Steam Outlet Position from the Reactor Vessel Bottom (m) Distance Between Insulation and Reactor Vessel Bottom (m)

11 RELAP5 Input Model (4) Annular gap area I.D Hot Leg Steam Venting Slots 14 Water Level APR1400 OPR1000 R Area (m 2 ) Shear Key 2 R Shear Key deg Height (m) Minimum Gap Area deg 3.50 R86.34 ICI Penetrations 120 deg Water Inlets 60 deg 120 deg 11

12 Heat Flux (MW/m 2 ) RELAP5 Input Model (5) Thermal load 1.4 Zone4 Zone3 1.2 Zone1 Zone Heat Flux (MW/m 2 ) OPR APR1000 APR Angle (degree) Angle (degree) MAAP4 Results for the APR1400 (from KHNP) Reduced Results for the OPR

13 RELAP5 Results & Discussion (1) Temporal coolant circulation mass flow rate Mass Flow Rate (kg/s) Water Inlet Water Outlet Steam Outlet Mass Flow Rate (kg/s) Water Inlet Water Outlet Steam Outlet Time (sec) OPR Time (sec) APR1400 Oscillatory Flow, APR1400 > OPR1000(Annular Gap Area, Thermal Load) Some water circulates through the steam outlet because two phase water level increases in the annular gap 13

14 RELAP5 Results & Discussion (2) Coolant injection temperature effect 2000 Mass Flow Rate (kg/s) APR1400 OPR Temperature ( O C) An increase in coolant injection temperature leads to an increase in the coolant circulation mass flow rate. 14

15 RELAP5 Results & Discussion (3) Local pressure and averaged void fraction (OPR1000) Local Pressure (bar) Coolant Injection Temp. = 25 o C Coolant Injection Temp. = 50 o C Coolant Injection Temp. = 80 o C Coolant Injection Temp. = 99 o C Local Void Fraction Coolant Injection Temp. = 25 o C Coolant Injection Temp. = 50 o C Coolant Injection Temp. = 80 o C Coolant Injection Temp. = 99 o C Height (m) Height (m) Coolant Injection Temp Bubble Generation Coolant Circulation Mass Flow Rate

16 RELAP5 Results & Discussion (4) Water level effect in the reactor cavity (OPR1000) Mass Flow Rate (kg/s) Level (m) If water level is lower than the outlet, an decrease in water level leads to an rapid decrease in the coolant circulation mass flow rate. 16

17 RELAP5 Results & Discussion (5) Local pressure and averaged void fraction (OPR1000) 1.8 Water Level = 6.95 m Water Level = 6.45 m Water Level = 5.35 m Water Level = 4.15 m Water Level = 3.35 m Local Pressure (bar) Water Level = 6.95 m Water Level = 6.45 m Water Level = 5.35 m Water Level = 4.15 m Water Level = 3.35 m Local Void Fraction Height (m) If water level is lower than water outlet, Height (m) Water level Local pressure Challenging distance in gap to flow out Circulation Mass Flow Rate 17

18 RELAP5 Results & Discussion (6) Driving mechanism of circulation flow Circulation flow = driving force pressure loss Driving force = pressure difference in gap and pool To increase driving force (higher void fraction) higher wall heat flux Higher coolant temperature Pressure loss = gap pressure, form & friction loss To decrease pressure loss Lower two-phase level in gap Larger gap size (minimum gap region) Uniform gap (reductions of form loss) 18

19 Conclusions (1) Natural circulation flow features of APR1400 and OPR1000 were examined by RELAP5 code. The coolant circulation mass flow rate at high power of the APR1400 is higher than that at low power of the OPR1000. The increase of the coolant injection temperature leads to an increase in the steam generation rate, which leads to an increase in the coolant circulation mass flow rate. The coolant injection temperature is not effective on the local pressure, but is effective on the local average void fraction. A decrease in the water level in the reactor cavity leads to a decrease in the local pressure at the lower region and an increase in the challenging distance in gap, which leads to a decrease in the coolant circulation mass flow rate. 19

20 Conclusions (2) It is concluded from the RELAP5 results that the present design of the reactor vessel insulation in the APR1400 and the OPR1000 is suitable for the IVR-ERVC. Verification experiments and a more detailed analysis are necessary to evaluate the IVR-ERVC in OPR

21 Toward the Robust and Resilient Nuclear System for the Highly Improbable Event Thank you for your attention! 21