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  • STEAM GENERATOR FOR PFBR AND FUTURE FBR

    S. AthmalingamIndira Gandhi Centre for Atomic Research

    Department of Atomic Energy, Kalpakkam

    India

    Technical Meeting on Innovative Heat Exchanger and Steam Generator Designs for Fast Reactors

    21-22 December 2011 at IAEA Headquarters, Vienna

  • LMFBR flow sheet

    PFBR Layout 2 loop concept with 4 SG per loop, Steam reheat cycle

  • Steam Generator Design concepts

    Phenix & FBTR

    US Demo Plant

    CRBRP

    TOP TUBESHEET

    THERMAL SHIELD

    EXPANSION BEND

    BOTTOM TUBESHEET

    SODIUM OUTLET

    SODIUM INLET

    WATER INLET

    STEAM OUTLET

    TUBE

    MAIN SUPPORT

    TOP TUBESHEET

    THERMAL SHIELD

    EXPANSION BEND

    BOTTOM TUBESHEET

    SODIUM OUTLET

    SODIUM INLET

    WATER INLET

    STEAM OUTLET

    TUBE

    MAIN SUPPORT

    PFBR SG

    BN 600

    SG for PFBR:Similar tubes (Ease Mfg.)ISI for tubes (Simpler)Thermal exp. between tubesNo stratification problem

  • Rolled and lip welded joint [BN600 SG]

    Raised spigot Internal bore butt welded joint

    BN600 SG PFBR SGPFR

    Evaporator

    Inset type joint

    Keeps weld in low stress

    Permits 100% Radiography

    Greater Ligament

    Avoids crevice

    Tube to Tube sheet joint configuration

  • Integral, counter flow & once through type- To reduce number of units and isolation devices

    23m long tubes / Bend to accommodate diff.thermal expansion- To reduce number of tube-tube sheet joints- To accommodate diff. thermal expansion between tubes

    Egg crate type tube supports- To reduce shell side pressure drop- Aluminized Inconel material to reduce fretting wear rate

    Ferritic steel construction- To attack SCC problem- Better thermal conductivity, hence enhances heat transfer- Better high temperature strength allows lower thickness

    Design code- Na-H2O boundary enhanced to RCC-MR Class 1- Remaining regions as per ASME Sec VIII Div. 1 with due

    modifications for enhanced design life

    Reliable operation: SGTF (Scaled model of PFBR SG)

    PFBR Steam Generator [SG]

    23 m

    TOP TUBESHEET

    THERMAL SHIELD

    EXPANSION BEND

    BOTTOM TUBESHEET

    SODIUM OUTLET

    SODIUM INLET

    WATER INLET

    STEAM OUTLET

    TUBE

    MAIN SUPPORT

    TOP TUBESHEET

    THERMAL SHIELD

    EXPANSION BEND

    BOTTOM TUBESHEET

    SODIUM OUTLET

    SODIUM INLET

    WATER INLET

    STEAM OUTLET

    TUBE

    MAIN SUPPORT

  • PFBR Steam Generator [SG]

    SG Main support- Conical support located at CG to reduce seismic excitation

    Orifice device at water inlet of each tube- To avoid flow instabilities for all operating conditions- Made of Alloy 800 to reduce erosion for 40 years life

    Thermal shields at tube sheet- To reduce transient loading to tube sheet for various plant

    transients

    - Also protects tube-tube sheet joints from transient loadings

    Tri-metallic joint for SG to sodium piping- To reduce thermal stress at the weld joint between ferritic

    steel SG (=12x10-6 k-1) and austenitic steel piping(=18x10-6 k-1)

    Safety features- Eddy current probe for ISI for tubes- Hydrogen in sodium detection system- Hydrogen in argon detection system- Isolation valves & Rupture discs at SG inlet and exit lines

    TOP TUBESHEET

    THERMAL SHIELD

    EXPANSION BEND

    BOTTOM TUBESHEET

    SODIUM OUTLET

    SODIUM INLET

    WATER INLET

    STEAM OUTLET

    TUBE

    MAIN SUPPORT

    TOP TUBESHEET

    THERMAL SHIELD

    EXPANSION BEND

    BOTTOM TUBESHEET

    SODIUM OUTLET

    SODIUM INLET

    WATER INLET

    STEAM OUTLET

    TUBE

    MAIN SUPPORT

    23 m

  • PFBR SG on Manufacture & Erection

    SG packed for dispatch

    SG during erection

  • Bring down total capital cost (Target: ~ 25% )

    Enhance equipment reliability

    Compact layout

    Bring down manufacturing schedule

    Enhance design life (40 to 60 years)

    Reduce ISI time & maintenance cost

    Adaptation from PFBR SG design & manufacturing experience:

    Material of construction : Mod. 9Cr-1Mo steel

    Broad design basis & Concept : Similar to PFBR

    Feasible by: 3 SG/Loop concept with increased tube length

    Goals for future FBR SG

  • For given plant parameters and tube size, increase in tube length Reduces no. of tubes, which reduces Tube T/S joint failure rate Increases water/steam velocity and overall heat transfer co-efficient Leads to reduction in overall heat transfer area requirement

    Maximum acceptable tube length ~ 34m (limited by water mass flux ) Present indigenous manufacturing capability is 30m

    PFBR

    CFBR

    Failure probability : 1x10-5 welds /annum (weld joint config.)

    Load factor and design life

    30 m long tube selectedfor SG of Future FBR

    Selection of Tube Length

  • Tube length Vs. number of joints/100MWth is plotted for PFBR plant parameters

    Worldwide OTSG data is also inline with the approach of increased tube length

    With evolution of design, number of tube- T/S joints are significantly reduced with employment of increased tube length

    Total No. of tube-T/S joints: PFBR 8752, CFBR 5196 (~41% Reduced)

    Tube Length & weld joints of worldwide OTSG

    Design Limits

  • Total cost of CFBR SG (3SG/loop, 30m tubes): 23% cheaper than PFBR SG

    Though pressure drop is higher, amortized operating cost is 18% lesser for CFBR than PFBR SG

    Associated systems and accessories cost is also 14% lesser than PFBR.

    Due to lesser No. of tube-tubesheet joints, amortized outage cost is also 36% lesser.

    Overall cost including outage cost: CFBR SG is ~21% cheaper than PFBR SG

    It also offers saving of ~26% in specific steel consumption & ~10 tonnes in sodium inventory

    Economics consideration

    OUTAGE COST FOR CFBR SG VS. PFBR SG (AN INDICATIVE STUDY)Based on weld joint failure rate:1x10-5 welds/annum

    Outage cost estimation: CFBR SG PFBR SG

    Thermal power of each module (MWth) 210.5 157.875Design life (Years) / Capacity factor 60 / 85% 40 / 75%No. of outage days in between refueling (For mid campaign) 180 120No. of joints per plant 5196 8752No. of outages in reactor life 3 3Each Outage cost (` crores) 99.56 43.92Present worth of total 3 outage cost (Rs. crores) 7.53 11.91

  • 100% power

    20% power

    Calculated with 1-D code DESOPT for various power conditions.

    Thermal Design of CFBR SG

    Flow rate / tube (kg/s)

    (T) deg. C

    0.128 20.7

    0.188 18.7

    0.194 17.8

    0.216 16.2

    PFBR

    CFBR

    Parameter PFBR CFBR % Change

    Flow thru each tube (kg/s) 0.128 0.216 68%

    Avg. H.T. Coeff. (W/m2K) 3680 4462 20%

    Avg. Heat transfer area (m2) 5216 4260 18.3%

  • Sodium side Heat transfer predicted by Subbotins correlation

    Convective heat transfer in 1 phase (water & steam)

    Mikheevs correlation

    Boundary determined by Tsat at given pressure

    Nucleate boiling term:

    Rohsenows correlation

    Critical quality by Konikov & Modnikov correlation

    Post dry-out region Miropolskys correlation

    Tsat(X=0)

    Dry-out

    X=1

    Correlations used in 1-D code DESOPT

  • Pressure drop of CFBR SG

    Pressure drop of sodium and water/steam side of SG along

    the tube length from bottom of SG

    % of Flow rate Vs. Total pressure drop

    on shell side of 30m SG

    Stepwise change in sodium side pressure is due to tube support arrangement at regular interval

    Higher change at 4m location is due to thermal expansion bend and supports

    For water side, after 20m length, large change in pressure is due to steam velocity

  • Comparison of CFBR SG with PFBR SG

    Description of steam generator CFBR PFBRThermal power per SG (MW) 210.5 157.9

    No. of steam generators/plant 6 8

    Design life (Years) / Cap. factor 60 / 85% 40 / 75%

    Tube length (m) / No. of tubes 30 / 433 23 / 547

    Tube size (ID / thk.) (mm) 12.6/2.4 12.6/2.3

    Pitch (mm) 32.4 32.2

    Shell inner diameter (mm) 736 831

    Effective heat transfer area (m2) 710 652

    Water side mass flux (kg/m2s) 1735 1030

    Steam outlet velocity (m/s) 29.8 17.8

    Tube side pressure drop (bars) 7.2 2.8

    Shell side pressure drop (bars) 1.4 0.8

    Critical heat flux (ID) (kW/m2) 566 579

    Peak heat flux (ID) (kW/m2) 836 694

    Sp. steel consumption (T/MWe) ~0.570 ~0.665

    Number of tube to tube sheet welds per MWe

    10.27 17.32

    A Comparative indication

    Reactor Specific Steel consumption T/MWe

    No. of tube T/S welds / MWe

    SPX 0.65 8.3 (Tube-tube)

    BN 600 3.0 27

    Phenix 2.64 16

    EFR - 11.51

    JSFR - 20.48

  • Parametric Sensitivity studies

    Effect of change in some parameters with thermal power of SGDescription % Reduction in

    thermal powerEffect of fouling (For 6 years period) 0.26Effect of tube thickness tolerance (+20%, -0%) 0.53Effect of tube thermal conductivity (by 10% lower) 0.50Combined effect of higher tube thickness and lower thermal conductivity

    1.08

    Combined effect of higher tube thickness, lower thermal conductivity and fouling

    1.34

    Maximum fouling resistance (For 6 years cleaning interval) changes the thermal power of SG by 0.26%

    Change in tube thickness by 20% reduces the thermal power by 0.53% which is double than the fouling case

    Change in thermal

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