Thermal and Stability Analyses on Supercritical Water-cooled Fast Reactor during Power-Raising Phase of Plant Startup

Transcription

1 Thermal and Stability Analyses on Supercritical Water-cooled Fast Reactor during Power-Raising Phase of Plant Startup Jiejin Cai, Yuki Ishiwatari, Satoshi Ikejiri and Yoshiaki Oka The University of Tokyo GoNERI reactor seminar, January, 09 1

2 Overview Background and purposes Thermal-Hydraulic Analysis Method Stability Analysis Method Criteria for Power-raising Phase of Startup Thermal and Stability Analysis Results and Discussions Summary 2

3 Advantages of SWFR inherits all the advantages of thermal spectrum SCWR, and no neutron moderator, high power density, compact core design, transmutation of MAs and LLFPs,... 3

4 About the SWFR CR guide tude Top dome Fuel Rod CR Guid Tube ZrH layer (thickness=1.3cm) Blanket Fuel Rod inlet nozzle Downcomer Blanket duct plate (SUS3) (a) Seed assembly (b) Blanket assembly Fuel assembly design Characteristics data Mixing plenum Seed Assembly Blanket Assembly Coolant flow path Thermal/Electric Power 2352/1035MW Core inlet temperature 280 o C Thermal efficiency 44% Core outlet temperature 500 o C Equivalent core diameter 2.67m Fuel pin diameter 7.6mm Active core height 2.7m P/D 1.14 Fuel bundle height 4.3m Number of fuel assembly [seed/blanket] 162/73 System pressure 25MPa Cladding material/thickness Stainless steel /0.43mm 4

5 SWFR Plant System Top dome CR guide tube RPV Turbine control valve Turbine bypass valve Exit valve Downcomer Feedwater pump Mixing plenum HP heaters Lower dome LP heaters 5

6 Startup procedures Pressurization to 25 MPa Start of Nuclear Heating Turbine Startup Line Switching Power & Temperature Raising Start of Nuclear Heating Turbine Startup Pressurization to 25 MPa Line Switching Power & Temperature Raising Constant pressure startup Sliding pressure startup Power-raising Phase??? 6

7 Research purposes Thermal consideration MCST Thermal-hydraulic stability consideration DR The available range of reactor power & feedwater flow rate to satisfy the thermal and stability criteria Because SWFR is a fast reactor with small reactivity feedback from the coolant density, coupled neutronics and thermal-hydraulic instability is not considered. 7

8 Thermal-Hydraulic Analysis Method The plant transient analysis code based on one-dimensional node junction model is used. Every parts are divided axially into different nodes of equal length. Top dome (12 meshes) Exit valves Turbine control valves Main coolant lines (10 meshes) CR guide tube (8 meshes) CR guide tube (8 meshes) CR guide tube (8 meshes) CR guide tube (8 meshes) Upper plenum ( meshes) Average downward seed channel (58 meshes) Clad Pellet Average upward seed channel (58 meshes) Clad Pellet Reactor coolant pumps Downcomer ( meshes, including mixing plenum) Average blanket channel (58 meshes) Clad Qsu Qsd Qsd Qb Qb Pellet Hottest blanket channel (58 meshes) Clad Hottest downward seed channel (58 meshes) Clad Hottest upward seed channel (58 meshes) Clad Qsu Pellet Pellet Pellet Mixing plenum Orifice Nodalization model 8

9 Thermal-Hydraulic Analysis Method (cont.) Start Analysis sequence Initial condition Inlet condition (Flow rate & temperature) Mass & Energy conservations Pressure drops of downcomer path, downward seed channel and blanket channel Control system Flow redistribution Momentum conservation check No Yes Change pressure Flow balance check at outlet boundary No Yes Pressure drops of average /hottest channels Flow redistribution Momentum conservation check No Yes Fuel rod heat conduction and radial heat transfer Next time step No Final time step? End Yes Flow chart of transient analysis Average and hottest channels are considered. The heat transfer coefficients in supercritical pressures are determined by Watts correlations. The properties of supercritical pressure water are determined by utilizing the JSME Steam Table in SI units (1980). 9

10 Stability Analysis Method Mathematical Models for stability analysis Fuel rod heat transfer model Fuel channel thermalhydraulic model Ex-core circulation system model Lumped parameter model with onedimensional radial heat transfer equations One-dimensional single-channel conservation equations single-phase flow for supercritical pressure An inlet orifice, a feedwater pipe, feedwater pump, an exit valve Frequency domain analysis is used. 10

11 Frequency Domain Linear Stability Analysis Establish governing equations Linearize governing equations δx δu G(s) δy δf Laplace transform to frequency domain H(s) Construct system transfer functions Obtain the poles of closed loop transfer function by solving the characteristic equation:1+ G(s) H(s) = 0 δ y δ x = 1+ G(s) G(s)H(s) The pole with the slowest response is used to determine the stability of the system 11

12 Block diagram for thermal-hydraulic stability δp ex =0 δp inlet Transfer function from pressure G(s) difference to inlet flow velocity δu inlet δu ex δp fb Energy conservation Mass conservation Momentum conservation H(s) δu 0 δ uˆ inlet G(s) = δ Pˆ 1 + G(s)H(s) inlet The hottest channel is analyzed for thermal-hydraulic stability analysis, because hotter channels are more unstable if all other factors are the same. 12

13 Checking the frequency response of the transfer function The present stability code is checked by the characteristics of the frequency response of the transfer function at steady state by using Bode plots. Gain [db] meshes 15 meshes 12 meshes meshes 40 meshes Frequency [rad/s] The gain response of closed loop transfer function (% power) 13

14 Checking the frequency response of the transfer function (cont.) Phase [deg] meshes 15 meshes meshes meshes 40 meshes Frequency [rad/s] The phase response of closed loop transfer function (% power) A resonant peak is observed at the frequency of about 16.0 rad/s due to the flow feedback effect. 14

15 Stability analysis simplification Hotta et. al. researched the parallel channel stability in BWR[1,2]. Their results suggest that all the parallel channel models show an excellent agreement in both the stability limit power and the limit-cycle amplitude, and the single channel stability analysis is enough if the upper/lower plenum is large enough. REFERENCES [1] A. Hotta, et. al., BWR Regional Instability Anallysis by TRAC0BF1-ENTRÉE I: Application to Density-wave Oscillation, Nuclear Technology, 135(1) 1-6. [2] A. Hotta, et. al., BWR Regional Instability Anallysis by TRAC0BF1-ENTRÉE II: Application to Ringhals Unit-1 Stability Test, Nuclear Technology, 135(1)

16 Stability analysis simplification (cont.) The volumes of the mixing plenum, and top dome are greatly larger than the fuel channels. The velocity of the coolant in the mixing plenum is much slower than that in the fuel channels. Neither upward/downward coupled stability nor parallel channels coupled stability is not dominant, and the single channel stability analysis is enough. CR guide tude Top dome Downcomer Mixing plenum Seed Assembly Blanket Assembly We carry out thermal-hydraulic stability analysis on upward seed channels, downward seed channels and blanket channels separately. 16

17 Criteria for Power-raising Phase of Startup The maximum cladding surface temperature (MCST) must not exceed the rated value of 681 o C. For normal operating conditions, the decay ratio of thermal-hydraulic stability must be less than 0.5. y(t) t 1 y 1 Decay ratio = y 2 /y 1 steady-state y 2 t 2 For all operating conditions, the decay ratio must be less than time (t) t 17

18 Results and discussions 18

19 Flow distribution between downward channels Downward seed assembly flow rate ratio(%) Core power(%) Feedwater flow rate (%) The downward seed assembly flow rate ratio during various core powers and various feedwater flow rates Wsd x, y Downward seed assembly flow rate ratio= W W sd x, y W sd, sd, = Flow rate in downward seed assembly channels at x% core power and y% feedwater flow rate, kg/s; (%) =Flow rate in downward seed assembly channels at % core power and % feedwater flow rate, kg/s. 19

20 Flow distribution between downward channels (cont.) Blanket assembly flow rate ratio(%) Core power(%) The blanket assembly flow rate ratio during various core powers and various feedwater flow rates Feedwater flow rate (%) Wbd x, y Blanket assembly flow rate ratio= (%) Wbd, = Flow rate in blanket assembly channels at x% core power and y% feedwater flow rate, kg/s; W W bd x, y bd, =Flow rate in blanket assembly channels at % core power and % feedwater flow rate, kg/s.

21 Flow distribution between downward channels (cont.) 60 Flow rate fraction (%) in downward seed(% inlet flow) in blanket (% inlet flow) in downward seed (50% inlet flow) in blanket (50% inlet flow) Core power (%) The flow rate fraction in downward seed assembly and blanket assembly for various core powers in % and 50% feedwater flow rate The flow rate ratio in downward seed assembly keeps decreasing slightly when the core power increases, and the flow rate ratio in blanket assembly increases slightly. 21

22 Flow rate in hottest channel Ratio_Hotave_sd Core power (%) Feedwater flow rate(%) Flow rate ratio between the hottest channel and average channel in downward seed assembly Ratio_Hotave_sd expresses the flow rate ratio between the hottest channel and average channel in downward seed assembly 22

23 Flow rate in hottest channel (cont.) Ratio_Hotave_b Core power (%) Flow rate ratio between the hottest channel and average channel in blanket assembly Feedwater flow rate(%) Ratio_Hotave_b means the flow rate ratio between the hottest channel and average channel in downward blanket assembly. 23

24 Flow rate in hottest channel (cont.) 1.6 Ratio_Hotave_su Core power (%) Feedwater flow rate(%) Flow rate ratio between the hottest channel and average channel in upward seed assembly Ratio_Hotave_su expresses the flow rate ratio between the hottest channel and average channel in upward seed assembly. 24

25 Thermal analysis Results 90 Feedwater flow rate (%) Core power (%) 681 Maximum linear power generation rate at BOEC is W/m MCST of blanket assembly during power-raising phase at BOEC The MCST of blanket assembly at BOEC for various powers and various feedwater flow rates during power-raising phase are small, which would satisfy the thermal criterion in most situations 25

26 Thermal analysis Results (cont.) Feedwater flow rate (%) Maximum linear power generation rate at EOEC is W/m Core power (%) MCST of blanket assembly during power-raising phase at EOEC 26

27 Thermal analysis Results (cont.) 90 Feedwater flow rate (%) Core power (%) MCST of upward seed assembly during power-raising phase 27

28 Thermal analysis Results (cont.) 90 Feedwater flow rate (%) Core power (%) MCST of downward seed assembly during power-raising phase It is found that during the low power (< 80%), the downward seed assembly is most limiting, and when the power is over 80%, the upward seed assembly is most limiting. 28

29 Thermal analysis Results (cont.) Feedwater flow rate (%) Available region satisfying thermal criterion Core power (%) Minimum inlet flow rates required to satisfy the thermal criterion during powerraising phase Larger power requires larger feedwater flow rate to ensure the heat balance. 29

30 Thermal-hydraulic stability analysis results Feedwater flow rate (%) Core power(%) Decay ratio of downward seed assembly during power-raising phase

31 Thermal-hydraulic stability analysis results (cont.) Feedwater flow rate (%) Decay ratio of blanket assembly during power-raising phase at BOEC Core power(%) We can see that all the decay ratios of blanket assembly in various powers and various feedwater flow rates during power-raising phase at BOEC are less than 0.5, which means that the instabilities would not occur in blanket assembly during power-raising phase at BOEC. 31

32 Thermal-hydraulic stability analysis results (cont.) 90 Feedwater flow rate (%) Core power(%) Decay ratio of blanket assembly during power-raising phase at EOEC 32

33 Thermal-hydraulic stability analysis results (cont.) Feedwater flow rate (%) Core power(%) Decay ratio of upward seed assembly during power-raising phase It is found that during the low power (< 80%), the downward seed assembly is most limiting, and when the power is over 80%, the upward seed assembly is most limiting. 33

34 Thermal-hydraulic stability analysis results (cont.) 90 Feedwater flow rate (%) required to satisfy stability criterion required to satisfy thermal criterion Core power (%) Minimum inlet flow rates considering both thermal and stability criteria during power-raising phase 34

35 Thermal and stability considerations Feedwater flow rate (%) Feedwater flow rate for power-raising phase Feedwater flow rate required to satisfy stability and thermal criteria Core power (%) Flow rates at partial power operations during power-raising phase 35

36 Thermal-hydraulic stability analysis results (cont.) Pressure drop (MPa) orifice pressure drop in blande assembly 2. orifice pressure drop in downward seed assembly 3. axial pressure drop in downward seed and blanket assembly 4. orifice pressure drop in upward seed assembly 5. axial pressure drop in upward seed assembly 6. feedwater flow rate Pressure drops at partial power operation of the SWFR Core power (%) Feedwater flow rate (%) The orifice pressure drops during power-raising phase are not large compared with the corresponding axial pressure drops. 36

37 Thermal and stability considerations (cont.) Decay ratio decay ratio of downward seed assembly decay ratio of blanket assembly decay ratio of upward seed assembly feedwater flow rate criterion Core power (%) pressure Thermal-hydraulic stability during power-raising phase The decay ratios of thermal-hydraulic stability during power raising are less than 0.5, and the stability criterion is satisfied Feedwater flow rate (%) / Pressure (MPa) 37

38 Thermal and stability considerations (cont.) 800 Temperature ( o C) o C MCST in upward seed assembly feedwater flow rate MCST in downward seed assembly core outlet temperature MCST in blanket assembly feedwater temperature Feedwater flow rate (%) Core power (%) Thermal analysis during power-raising phase The MCST is below the rated value of 681 o C, and thus the thermal criterion is satisfied during power-raising phase of startup. 38

39 Summary Considering the pressure drop balance, we get the flow rate distribution among the parallel flow paths, namely, the downward seed assemblies, downward blanket assemblies and downcomer. The available range of the reactor power and feedwater flow rate can be obtained, which satisfies the thermal and stability limiting criteria. 39

40 Thank you 40