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
