Chapter 7. Design of Steam Generator

Transcription

1 Nuclear Systems Design Chapter 7. Design of Steam Generator Prof. Hee Cheon NO

2 7.1 Overview and Current Issues of S/G Essential Roles of S/G 2

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4 7.1.2 S/G and Its Interfacing Interfacing system of S/G 4

5 Internal system of S/G and Design Values 5

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7 7.1.3 Three Types of S/G Type 1 : Once-through S/G Primary Flow is Downward Secondary Up 7

8 Type 2 : Vertical U-Tube S/G Primary Flow is Up & Down Secondary Up 8

9 Type 3 : Horizontal S/G Primary Flow is Horizontal Secondary Up 9

10 7.1.4 Thermal Behavior in the Secondary Side of S/G Slightly subcooled swirl flow in the downcomer due to saturated rotational flow by primary separators Strong unsymmetrical void distribution between the cold and hot sides Churn-turbulent flow regime is dominant 10

11 7.1.5 Main Current Issues of S/G Tube degradation : Degradation of thermal efficiency, more overall inspection, More radiation exposure of maintenance personnel, high possibility of SG tube break accident SG water level control : Frequent Reactor trip by failure of S/G water level control 11

12 Condensation-induced waterhammer in S/G : Serious structural effect on feedwater lines Design of SG separators : Excessive moisture Excessive costly maintenance Importance of SG role on SB-LOCA : Heat sink by reflux condensation 12

13 7.1.6 S/G Reliability Main Problems of S/G Tube material corrosion 13

14 Tube material corrosion : Wastage or thinning : cyclic boiling and deposition in alternative wetting and drying zone of sludge Primary water initiated cracking Secondary water initiated cracking Pitting 14

15 Tube support & tubesheet corrosion 15

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17 Tube support and tubesheet corrosion : Denting : Cyclic boiling and deposition in crevices by wetting, dryout, and rewetting 17

18 Mechanical damage Mechanical damage : Tube fretting Fatigue cracking 18

19 7.2 Design Improvement of S/G Design Parameters Affecting Reliability of S/G Water chemistry choice : Solid treatment (Phosphate treatment) AVT (All-Volatile Treatment) Material design choices : Tubes : Inconel 600 Inconel 800 More SCC Resistant but lower thermal conductivity 19

20 Tube SupportPlates : Carbon Steel Stainless Steel More Denting Resistant Secondary Plant: Less Cu + Carbon Steel Decelerating Denting Stainless Steel Condenser Tubes: Aluminium Titanium More Chrolide Resistant 20

21 Design choices: Stagnant Regions (near Tube Sheets, Tube SupportPlates) : More Chemistry Concentration 21

22 7.2.2 Design Modification of S/G Objectives of design change Larger circulation ratio : Decreasing potential for local chemical concentration More corrosion resistant materials Increasing secondary-side access for inspection and maintenance 22

23 Practical example : Model F S/G Design Changes WESTINGHOUSE MODEL F STEAM GENERATOR DESIGN CHANGES SUMMARY CHANGES Quatrefoil tube support Ferritic stainless steel tube supports Thermally treated Inconel 600 tubing Access openings Wet layup recirculation connection Separator upgrading PURPOSES Increase circulation Increase margin against corrosion Increase margin against Corrosion Enhance maintainability Enhance maintainability Enhance separation 23

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29 Feedring Design: Steam-Driven Waterhammer in S/G 29

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32 Possible sequence events leading to condensation-induced water hammer. [1] 32

33 [2] 33

34 [3] 34

35 [4] 35

36 Solutions : Change pipe layout : Short horizontal pipe length Less acceleration Generation of smaller pressure wave Installation of J nozzles : Problem : some drainage by a built-in leakage at the thermal sleeve (designed for accommodation of thermal expansion) Auxiliary feedwater flow control : Limitation of highly subcooled auxiliary feedwater flow to limit the amount of steam condensed 36

37 Separator: gravitational/primary/secondary(dryer) separators Gravitational Separator: Empty space between primary and secondary separators Very effective to eliminate large droplets 37

38 Primary Separator : Separation through centrifugal force Two competitive requirements : Good separation : vane design to produce large centrifugal force Low pressure drop : vane design to produce small centrifugal force 38

39 Moisture separator Combustion Engineering Type Seperstor 39

40 Three-Dimensional Visualization of Westingouse Steam separator Geomety 40

41 Secondary Separator (Dryer): Chevron type dryer Very effective to eliminate small droplets 41

42 7.3 Design Analysis S/G Prediction of Circulation Ratio Circulation Ratio : CR g h a h g a h K A h Q h h 1/ 2 {[ f ( D f 2 ) g ( g 2 )]/ [ /(2 )]} ( B fg / SG)(1 F / fg ) Parametric effects on CR : Note: A decrease in form loss of tube support plates drives to increase CR. 42

43 Prediction of Circulation Ratio CR m / m m / m m / ( m ) 1/ D F D s D e D e recirculation ratio m / m CR 1 mass m m m D F R energy : Q m ( h h ) m ( h h ) R D 0 i F s F F CR m / m ( h h ) / ( h h ) ( m / Q )( h h ) ( m / Q ) h (1 h / h ) D F s F 0 i D SG g F D SG fg F fg where h h h F f F Measurable quantities : Q, h ( p ), h SG fg s F Unmeasurable quantitiy : m D 43

44 Estimation of : momentum : p p where p [ K / (2 A )] m 2 2 f B D 2 p gh g ( ) dh gh g( ) h d f D g g f f f D g g f f 0 gh g( ) h g( h h ) g( h ) f D g g f f 2 f D f 2 g f 2 Then, we have m D driving force fricton form loss 1/2 m {[ g( h h ) g( h )] / [ K / (2 )]} A D f D f 2 Circulation ratio becomes h g f 2 B CR g h h g h K A h Q h h 1/2 {[ f ( D f 2 ) g( f 2 )] / [ / (2 )]} ( B fg / SG)(1 F / fg) 2 44

45 7.3.2 Determination of Steam Pressure in the S/G Equation for steam pressure: ( UA) T / ( h h ) [( p p )2 / K ] A 1/2 SG ln s F s back s s s where, Tln ( THL TCL ) / ln[( THL Ts ) /( TCL Ts )] Rate of bubble generation in the steam generator (W b ) = steam flow rate in the steam lines (W s ) 45

46 The steam pressure will be increased until the steam flow rate from the steam generator is the same the bubble generation rate: Rate of bubble generation in the steam generator (W b ) W Q / ( h h ) ( UA) T / ( h h ) b SG s F SG ln s F steam flow rate in the steam lines (W s ) ( p p ) K u / 2 K W / ( A ) W [( p p ) / K ] A /2 s back s s s s s s s s s back s s s 46

47 design requirement : maximum pot press=1.5bar design pipe diameter: Q h P P K D 4 4Q 1/2 K 1/4 Dp ( ) [ ] h 2 ( P P ) 1/2 2 / fg [2( pot a ) / ] ( P) fg pot a 47

48 Deter mination of SG pressure Input A, Q, T, T ; Output p, m, W w Rx pin pout SG s tu Q m ( h h ) UA T ; W m ( h h ) SG s s F w LN tu s s Cinlet Q Q UA T T Rx SG w LN SG Q m ( h h ) m SG s s F s W m ( h h ) W tu s turbine, inlet turbine, outlet tu Note : h ~ h s ; h ~ h turbine, inlet turbine, outlet condenser, inlet where T ( T T ) / ln( T / T ) ln [( T T ) ( T T )] / ln[( T T ) / ( T T )] pin SG pout SG pin SG pout SG Comparison : T ( T T ) pavg SG 48

49 Estimation of Reactor Thermal Power by Secondary Calorimetric Method Methods of Rx power measurement in real time to check whether Rx power is operated at or below the licensed Rx power: Measurement of incore neutron det ector : not real time Q Rx K thermal flux Measurement of primary flow rate( W ) : l arg e pressure drop primary Q Q Q Q W c ( T T ); Rx RCP loss SG primary p, primary hot cold Secondary carolim etric method : feedwater flow measurement( W ); accurate and real time method Q Q Q Q Q Q Q Q Rx RCP loss SG Rx SG RCP loss Q W h W h Q W ( h h ) SG F F S S SG F S F With measurement of W, we can obtain Q, Q in real time. F SG Rx F 49

50 Estimation of feedwater flow through the venturi tube : W C F T D p D D 2 4 F d a( F )( ph / 4) (2 F ) /[1 ( ph / F ) ] where F ( T ) a D th F, D F : area factor of the nozzle for thermal expansion : diameters of the throat of the venturi tube and feedwater line C d : discharge coefficient measured at the standard p and T 50

51 Degradation of feedwater flow measurement instrument Copper plate-out problem on the venturi nozzle : Cu oxides and hydroxides from tubes in feedwater heaters and MSR + magnetite (Fe3O4) formed on the nozzle: (CiO) x (Fe 3 O 4 ) y Copper plate-out indicated dp > true dp increase in nozzle surface roughness indicated feedwater flow > true feedwater flow indicated power > true power if indicated power is higher than licensed power, reactor power is reduced reduction of load reduction of electric power 51

52 Solutions maintaining a clean venturi nozzle maintaining an air-tight secondary system and a clean condenser replacing cast-iron nozzle with stainless steel nozzle replacing Cu-containing tubes with stainless steel tubes heat rate monitoring system 52

53 7.3.4 S/G Sizing Cost Analysis : Yearly Cost during Lifetime: C A ( RC E C ) SG a p 1 2 C : yearly cost during life time C a : cost per unit area C p : cost per unit energy E : pumping power per unit area : pump running time n n R : capital recovery factor yearly rate due to depression = i( i 1) /[ 1 i 1] i : interest rate n : steam generator life (yr) 1 : yearly capital cost including interest during life time 2 : yearly operating cost Six-Tenths Rule: C C ( A / A ) a a0 SG SG

54 Pumping power : Pumping Power per Unit Area = head P m / ( A ) P Q / A loss p SG loss SG Note : P Q ( P A ) u F u loss loss f Pressure Loss : head P head loss p ( P P P P ) ( K fl / d K K ) u 2 2 in f bending out in i b out p p Power = Work ( F x) dx F F u dt dt dt 54

55 Wall thickness : Wall thickness by ASME Power Boiler Code Formula: t ( d d ) / 2 p d /(2S 2 yp ) o i p o p where 55

56 S/G Tube Area : Primary and secondary temperature difference at the same axial position : T ( z) T q ( z)( R R R R ) q ( z) R C( q ( z)) p s p m f s pmf 1/3 where 56

57 Temperature decrement between (z+dz) and z : ( T ( z dz) T ) ( T ( z) T ) T ( z dz) T ( z) p s p s p p dt z R C q z dq z 2/3 p( ) [ pmf ( / 3)( ( )) ] ( ) Increment of heat transfer rate between (z+dz) and z: da( z) dq( z) / q ( z) m c dt / q ( z) p p p m c R C q z dq z q z 2/3 p p[ pmf ( / 3)( ( )) ] ( ) / ( ) Integrating da from the inlet and outlet of the tubes yields out in da A Q T T R ln q z C q z 2/3 out SG [ SG / ( pin pout )][ pmf ( ( )) ( / 2)( ( )) ] in f ( Q, T, T, R, q (0), q ( L )] SG pin pout pmf SG 57

58 To get the expression of q'' in terms of temperature we need to solve 3 Rpmf X CX T 0 where X q z T T T 1/3 ( ), p s Solution of the above equation : b 2 3 X a ( a b ) a ( a b ) where a T /(2 R ), b C /(3 R ) pmf pmf

59 local heat flux in terms of parameters: q ( z 0) X g ( T T, R ), pin S pmf q ( z L ) X g ( T T, R ) 3 SG 2 2 pout S pmf Final expression of the total tube area: A f ( Q, T, T, m, R, T or p ) SG SG pin pout p pmf S S 59

60 Design Procedure : Input : Output : Get t and Q, d, T, m, p, p A, L SG o pin p s p d i u p With guessed, the total number of tube : N SG N m u d 2 SG p / ( p p i / 4) SG SG Get Get T, R, q ( z 0), q ( z L ) pout pmf SG A SG and L Get pumping power. SG Other way to det er min e A : A Q / ( U T ) SG SG LN where SG T [( T T ) ( T T )] / ln[( T T ) / ( T T )] LN pin SG pout SG pin SG pout SG Get yearly cost during lifetime. Check whether C is an optimal value or not. Check whether p loss is reasonable or not. 60