International Conference on Fast Reactors and Related Fuel Cycles: Safe Technologies and Sustainable Scenarios (FR13) Hideki Kamide 1 A. Ono 1, N. Kimura 1, J. Endoh 2 and O. Watanabe 2 1: Japan Atomic Energy Agency (JAEA), 2: Mitsubishi FBR Systems Inc. (MFBR)
(1) Core Inter-Wrapper Flow Natural convection in Core Barrel Inter-Subassembly Heat Transfer DRACS (1 loop) PRACS (2 loops) Heat Exchanger of PRACS (2) DHRS-Loop Onset of NC Natural draft -> Primary loop SG (3) Air Cooler Freezing Over-cooling, Long-term SBO without control DHX RV IHX+ Pump Primary Heat Transportation System: 2 loops Secondary Heat Transportation System Detail of IHX (4) PRACS HX Bypass flow and Thermal stratification Heat Transportation Systems in JSFR
Objectives Decay Heat Removal System (DHRS) Main A/C Natural circulation phenomena Applicability of 3D simulation to natural circulation PRACS HX Blower IHX DHX Core Pump EMF Secondary HT System Pump Primary HT System Test loop: PLANDTL
1. Steady State Sodium Experiment on IWF F A E B D C Model Specifications Core: 7-subassembly model Center subassembly: 1/1 Partial model Steady state forced convection test Heated length: 1m Decay heat: Heat flux of 1-3% Pin pitch /Diameter: 1.19 Flow rate: NC flow velocity level (0.5-2%) Fuel pin diameter: 8.3 mm DRACS: Cold fluid in upper plenum Gap between subassemblies: 7mm PRACS: Homogeneous temperature in DRACS or PRACS can be selected as upper plenum and S/A outlet Decay heat removal system 4
Extremely low flow rate conditions through Core DRACS (IWF), Flow velocity in pin bundle: zero to 1% Core Power 1.5% Axial temperature distributions in central subassembly along center pin Transverse temperature distributions at top of heated length of the core
Non-dimensional Peak Temp. Highest temperature in the core Balance between Core power and Removed heat Heat(IWF) Q Cp A g V g T Q / F Cp A b V b T Q / F A g V g A b V b Balance between Buoyancy force and Pressure loss in Gap region g T Q / F L L R D g f 1 2 V g 2 f 0.316Re 1/ 4 Buoyancy force in gap: Gr Inertial force in pin bundle: Re Gr g T Q / F D g 3 2, Re V b D b 1.2 1 0.8 0.6 0.4 Non-dimensional parameter of heat removal by IWF 4/ 7 Gr Heat(IWF) Q C Re Core Pow er 1.0% 1.5% 2.0% 0 2 4 6 8 10 12 C Gr 4/7 /Re The highest temperature in the core
DHX Core Primary Loop PRACS Pump PRACS HX IHX Pump EMF Sec. Loop A/C Blower Transient Tests including Primary Loop, Secondary Loop, PRACS Loop, and Air Stack Basic Case Prim. and Sec. Loops: Switch from F.C. to N.C. PRACS: Standby Operation (Damper Closed) to Startup (Damper Open) under N.C. conditions
Temper atur e ( C) F lo w r a t e ( l/ m in ) F lo w r a t e ( l/ m in ) A ir V e lo c it y ( m / s ) P o w e r ( k W ) Temper atur e ( C) 2 0 0 1 5 0 1 0 0 50 0 Core Power and Flow Rates (Short Span) 600 550 500 450 400 350 300 250 P r im a r y F lo w 8 0 0 S e c o n d a r y F lo w 6 0 0 P u m p S t o p 2 0 0 C o r e P o w e r 0 0 1 0 0 2 0 0 3 0 0 4 0 0 5 0 0 T im e ( s ) Top of Heat ed Par t at Cent er Subchannel Cor e I nlet M iddle of Upper Neut r on Shielding 0 100 200 300 400 500 Tim e ( s) Temperatures in Core (Short Span) 1 0 0 0 4 0 0 100 80 60 40 20 0 P r im a r y F lo w S e c o d a r y F lo w V a lv e Clo s e 1 A ir V e lo c it y 0 0 100020003000400050006000 T im e ( s ) Core Power and Flow Rates (Long) 600 550 500 450 400 350 300 250 Top of Heat ed Par t at Cent er Subc hannel M iddle of Upper Neut r on Shielding Cor e I nlet 0 1 0 0 0 2 0 0 0 3 0 0 0 4 0 0 0 5 0 0 0 6 0 0 0 Tim e ( s ) Temperatures in Core (Long) 6 5 4 3 2
Temper atur e ( C) F lo w r a t e ( l/ m in A ir V e lo c it y ( m / s ) 50 5 40 30 P RA CS F lo w 4 3 PRACS A/C 20 A ir V e lo c it y in A C 2 10 1 DHX Core Pump Primary Loop PRACS HX IHX Pump EMF Blower Sec. Loop 0 450 400 350 300 250 200 0 100020003000400050006000 T im e ( s ) Air Flow and PRACS Flow Rates PRACS O ut let AC Na O ut let PRACS HX I nlet AC Air O ut let AC Air Duc t 0 1 0 0 0 2 0 0 0 3 0 0 0 4 0 0 0 5 0 0 0 6 0 0 0 Tim e ( s ) Temperatures at Air Duct, A/C, and PRACS HX 0
Low Temperature Operation of Air Cooler Risk of LOHRS: Freezing at Air Cooler caused by long term Natural Circulation operation without control, i.e., SBO N.C. Behavior prior to Freezing is significant. Temperatures at AC and Flow rate in PRACS loop
Three dimensional phenomena influencing Natural Circulation Thermal stratification: Change of mixing volume Delay of low temperature fluid circulation Thermal stress on structural wall Bypass flow in Heat Exchanger Change of heat exchange area and heat removal capacity Temperature distribution across tube plate Complicated Phenomena in Core Inter-wrapper flow Heat transfer between subasemblies in radial direction Natural draft in air cooler and stack Full 3D modeling of primary system and DHRS system Plenum, Core, Heat exchanger, piping 3D Simulation Methods STAR-CD: Mother code TREFOIL: Core thermal-hydraulics 1-D code: Secondary systems of IHX
Application to Sodium Test 3.3 million meshes Tube of heat exchanger Fuel S/A IHX tubes PRACS Heat Exchanger Tubes Three-dimensional analysis model Thermal stratification and bypass flow are examined in IHX inlet plenum where PRACS heat exchanger is installed.
PRACS Steady State Heat Removal Primary loop flow rate is a experimental parameter. Tree-1 Tree-2 TC tree Calculated Temperature Contours PRACS tubes Bypass flow is well simulated by 3D calculation Measured Temperature Distributions
Thermal Stratification due to PRACS Heat Removal Transient experiment from forced to natural circulations in the primary system and PRACS secondary system Thermal stratification occurred and developed due to cold sodium provided by PRACS and was well simulated.
Conclusions Sodium Experiments for SFR Natural Circulation DHR Inter-wrapper Flow (IWF) in a Core High potential to remove heat from core fuel subassemblies Simulation of IWF is significant issue. Onset of natural circulation in PRACS and primary loop Smooth increases of air and sodium flows in stack and loops Development of air flow is faster than that of PRACS sodium flow. Slow and steadily increase of pressure loss coefficient prior to freezing in low temperature operation of Air Cooler 3D simulation method and application to sodium test 3D simulation method Full 3D modeling of primary system including core and piping Decay heat removal system including air stack is modeled. Comparison with Sodium tests Bypass flow and thermal stratification in IHX plenum equipped with PRACS heat exchanger were well simulated by 3D simulation.
End of Presentation
Pressure loss coefficient [-] Viscosity [m 2 /s] Pressure loss coefficient in PRACS loop 70 1 10-6 60 8 10-7 50 40 Kinetic viscosity 6 10-7 4 10-7 30 Run No. 1 Run No. 2 2 10-7 Run No. 3 20 0 100 150 200 250 300 350 400 Sodium temperature at AC outlet [ÞC] Kinetic viscocity (previous) Increase of pressure loss : AC outlet temperature was below 200 C Kinetic viscosity (present-1) However, it was slow transient as shown before. Kinetic viscosity (present-2)
T e m p e r a T t e u m r e p e Experimental Conditions: Primary Flow (l/min) 100: Gr/Re 2 Same as JSFR 300: N.C. Velocity 600: Higher Velocity PRACS Sec. Side Forced Flow Conditions Heat Removal ~130 kw Heat Flux: 70% of that in JSFR Gr: L = Height of HX tubes T between Prim. and Sec. sides Re: L= based on Bundle Cross Section TC Tree PRACS HX TC Tree 5 0 0 4 8 0 4 6 0 4 4 0 4 2 0 Thermocouple Positions in IHX Inlet Plenum 4 0 0-2 0-01 0 0 0 1 0 02 P o s it io n 5 0 0 4 8 0 Higher Tube positions 4 6 0 P F 1 4 4 N P F 3 0. C. V e lo c P F 6 4 2 0 2 S im ila r G 4 0 0-2 0-01 0 0 0 1 0 02 P o s it io n
Heat Transfer Coefficient (W/m 2 K) 10 4 8 x 10 3 5 x 10 3 C orrelation Ex periment C orrelation H = D o N u N u = 0.625 Pe 0.4 10 3 0 50 100 150 200 Pe Comparison of Heat Transfer Coefficients at Tube Outer Surface between Exp. and Design