PWR Description
Jacopo Buongiorno
Associa t e Pr of essor of Nuc l ear Science and Engineering
22.06 : Engineering of Nuclear Systems
Pressurized Water Reactor (PWR)
Public domain image from wikipedia.
SCHEMATIC O F A PWR
Major PWR vendors include Westinghouse, Areva and Mitsubishi
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PWR C oolant Circuits
INDIRECT CYCLE: Primary and Secondary Coolant Loops
Sin g le Phase ( Li q uid ) Reactor Coolant
[T in =287.7 ˚ C, T out =324 ˚ C, P=15.2 MPa, T sat = 343.3 ˚ C]
Two-Phase (Steam-Water) Power Conversion Cycle Loop
[T SG,in =227 ˚ C, T SG,out =285 ˚ C, P=6.9 MPa, T sat =285 ˚ C]
[ T Condenser = 37.8 ˚ C, P=6.6 kPa ]
Phase D iagram of Water
Pressure
Saturation line
15.2
6 . 9
0.1
0.006
PWR pr i mary system PWR secondary system
Liquid
Condenser
V apor
38 100 227 285 343 T emperature
288 324
[ C]
PWR Vessel, Core and Primary S ystem
A RRANGEMENT OF THE PRIMARY SYSTEM FOR A WESTINGHOUSE 4-LOOP PWR
A.V. Nero, Jr., A Gui d ebook t o N u cl ear React o rs , 1979
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FLOW PATH WITHIN REACTOR VESSEL
C R gu i de t u be s
U p pe r s u pp o r t pl a t e
B ar r el f l an g e
Ho t n o z z le
W a t e r i n a t W a te r o u t a t
28 8 C 32 4 C
C o ld n o z z le
T o p of ac t i v e f u el
C o r e
B o tt o m o f a c ti v e f u e l
Lo w er c o r e p l at e
REACTOR VESSEL AND INTERNALS
Public domain image from Wikipedia.
Pi ct ures from : M. Kanda, Im provem e nt i n US-A PW R desi gn from l e ssons l earned i n Japanese PW R s .IC A P P - 0 7 . M a y 2007 (t op), and EPR brochure avai l a bl e at www.areva.com (b o tto m two )
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TYPICAL 4-LOOP REACTOR VESSE L PARAMETERS
Ove r al l l e n g t h of ass e m b led v e ssel , cl os ure h ead, a n d nozzl es 13 .3 6 m Insi de di a m et er of sh e l l 4 . 39 m
Radi us fr om cent er of ves s el t o nozzl e face
Inl e t 3. 33 m
O ut l et 3 . 12 m
Nom i nal cl add i ng t h i c k n ess 5. 56 m m
M i nim u m cl addi n g thic kne ss 3. 18 m m
Coola n t volum e w ith c o re an d inter n als in pl ace 134.2 m 3
Ope r at i n g pres sure 15 .5 1 MPa
Desi g n pres s ur e 17 . 2 4 MPa
Des i g n t e m p erat ure 34 3. 3 ° C
V e ssel m ate ria l Car b o n steel
C l a ddi ng m a te r i a l Sta i n l ess stee l
Num b er of ves s el m a t e ri al surveillance ca ps ules, to tal 8
TYPICAL 4 - LOOP CORE
Image by MIT OpenCourseWare.
Masche, G., System s Sum m a ry: W PW R NPP, 1971
Geometry of the fuel
Image by MIT OpenCourseWare.
Image by MIT OpenCourseWare.
Cross Section of a Representative Fuel Pin (not drawn to scale)
|
m m (in.) |
BWR |
PWR |
|
2r o |
10.40 (0.409) |
8.20 (0.323) |
|
2r co |
12.27 (0.483) |
9.50 (0.374) |
|
t |
0.813 (0.032) |
0.57 (0.023) |
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Why the fuel/clad gap?
Provides clearance f or fuel pellet insertion during fabrication
Accommodates fuel swelling without breaking the clad
Filled with helium g as
Example of a Cracked Fuel Cross Section
Source: T odreas & Kazimi, V o l. I, p. 333
14
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TYPICAL FUEL R OD PARAMETERS
|
Out side diam ete r |
9.50 m m |
|
Cla dding thi c knes s |
0.57 m m |
|
Diametral g ap |
0 . 1 6 6 m m |
|
Pelle t diam ete r |
8.19 m m |
|
Pitch |
12.6 cm |
|
Rods arra y in asse mbl y |
17x17 |
|
Fue l rods per a s sembly |
264 |
Total num be r of fuel rods i n c o re 50,952
CUTAWAY OF TYPICAL ROD CLUSTER CONTROL ASSEMBLY (RCCA)
From : EPR brochure. Available at www.areva.com
Masche, G., System s Sum m a ry: W PW R NPP, 1971
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PWR Control Rod ( Westin g house RCCA ) Made of Ag-In-Cd (“black” rods for scram) or Inconel (“gray” rods for fine tuning)
Public domain image from wikipedia.
Control rod guide tube (24) Instrument thimble
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Enrichment = 5 W / U 235
0
Enrichment = 6 W / U 235
0
Enrichment = 7 W / U 235
0
Other means to control reactivity in PWRs
Bor on (boric acid, H 3 BO 3 ) dissolved in coolant . Compensates for loss of reactivity due to fuel burnup. High concentration at BOC (beginning of cycle), progressively decreased to zero a t E OC (end of cycle)
Pr os: uniform absorption throughout core, concentration is easily controlled Cons: makes coolant sli g htl y acidic ( re q uires addition of other chemicals to re- equilibrate pH), can deposit (come out of solution) as crud on fuel rods, can make moderator reactivity feedback positive at high concentration
Core critical boron concentration (ppm)
8000
7000
6000
5000
4000
3000
2000
1000
0
0 5 10 15 20 25 30 35 40 45 50
Exposure (GWD/MTU)
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No Poison
36 BA Pins
24 BA Pins
40 BA Pins
32 BA Pins
44 BA Pins
Other means to control reactivity in PWRs (2)
Burnable absorbers (“poisons”) loaded in fuel . Gd (Gd 2 O 3 ) h a s higher a than 235 U, thus it “burns” faster than fuel, which tends to increase k ef f over time .
Pr os: no impact on coolant corrosion or moderator reactivity feedback
Cons: lowers melting point and thermal conductivity of UO 2 , cannot burn out completely by EOC
1.20
1.15
1.10
k
1.05
1.00
0.95
0 10 20 30 40 50 60
Assembly exposure (GWD/MTU)
Image by MIT OpenCourseWare.
PWR GRID SPACERS
From: Mitsubishi US- A PWR Fuel and core desi g n . DOE Techn i ca l session UAP-HF-07063 . J une 29, 2007.
Masche, G., System s Sum m a ry: W PW R NPP, 1971
Hold fuel rods in place p revent excessive vibrations
Have mixing vanes enhance coolant mixing and heat transfer
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Connection of PWR Core Desi g n to Neutronics
Why is Zr used as structural material in fuel assemblies? What functions does water perform?
What determines the fuel rod spacing? Why are the fuel rods so small?
Why are the control rods arranged in clusters?
Why i s boron dissolved in the c oolant? What is Gd used for?
PWR Bundle D esign Advances
Extended burnup features
Advanced cladding ( ZIRL O , M5 )
Annular blankets
Larger gas plena
Improved mechanical performance
Improved debris filters
Low growth, wear-resistant materials Improved economic and operational performance
Natural uranium blankets
Flow mixing grids to enhance margin to DNB Reduced O&M costs
Low cobalt steel alloys to reduce exposure
Reduced inspection requirements
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5. Fuel Assembiles
Number of assemblies
Number of heated rods per assembly Fuel rod pitch (mm)
Fuel assembly pitch (mm)
Number of grids per assembly
Fuel assembly ef fective flow area (m 2 )
Location of first spacer grid above beginning of heated length (m)
Grid spacing (m) Grid type
Number of control rod thimbles per assembly Number of instrument tubes
Guide tube outer diameter (mm)
6. Rod Cluster Control Assemblies
Neutron absorbing material
193
264
12.6
215
7
0.02458
0.3048
0.508
L- grid * 24
1
12.243
Ag-In-Cd
Cladding material
T ype 304 SS
Cladding thickness (mm)
0.46
Number of clusters Full/Part length
53/8
Number of absorber rods per cluster
24
*Employs mixing vanes
REPRESENTATIVE CHARACTERISTICS OF PWRs
Parameter
4- loop PWR
Parameter
4- loop PWR
1. Plant
50,952
94
8.19
9.5
0.57
Zircaloy-4
3.66
4. Fuel Rods
T otal number
Fuel density (% of theoretical) Fuel pellet diameter (mm) Fuel rod diameter (mm) Cladding thickness (mm) Cladding material
Active fuel height (m)
3,729
A verage core inlet mass flux (kg/m 2 -s)
17.7
Ef fective core flow rate for heat removal (Mg/s)
18.63
T otal core flow rate (Mg/s)
33.4
A verage temperature rise in reactor ( o C)
292.7
Core inlet temperature ( o C)
15.51
System pressure (MPa)
3. Primary Coolant
2.5
Allowable core total peaking factor (F Q )
1.65
Design axial enthalpy rise peaking factor (F h )
598.8
A verage heat flux (kW/m 2 )
5546.3
Active heat transfer surface area (m 2 )
4.747
Ef fective core flow area (m 2 )
32.6
Core volume (m 3 )
104.5
Rated power density (kW/L)
3.76 /3.87
Core barrel inside diameter/outside diameter (m)
2. Core
97.4
Power generated in the fuel (%)
2.6
Power generated directly in coolant (%)
1 150
Plant electrical output
34
T otal plant thermal ef ficiency (%)
341 1
Reactor thermal power (MWth)
4
Number of primary loops
Image by MIT OpenCourseWare.
A .V. Ne r o, J r ., A Gui d ebook to Nuclea r R eacto r s , 1 979.
PWR PRESSURIZER
Pressurizer (Saturated Liquid-Steam System: P=15.5 MPa, T=344.7 ˚ C) Controls pressure in the primary system
Fro m co ld le g
L i qui d Sp r a y
St ea m - P ressure can be raised by heating
2 m water (electrically)
L i qui d - P ressure can be lowered by
Ele c t r ic he a t er s condensing steam (on sprayed droplets)
Sur ge Lin e
Ho t le g
Number and type Overall height Overall diameter W ater volume Steam volume Design pressure Design temperature T ype of heaters Number of heaters
Installed heater power Number of relief valves Number of safety valves Spray rate
Pr essur e transient Continuous
1 T wo-phase water and steam pressurizer
16.08 m
2.35 m
30.58 cu m
20.39 cu m
17.2 MPa
360 o C
Electric immersion 78
1800 kW
2 Power -operated
3 Self-actuating
3028 L/m
3.79 L/m
Shell material Dry weight
Normal operating weight
Flooded weight (21.1 o C)
Mn-Mo steel, clad internally with stainless steel 106,594 kg
125, 191 kg
157,542 kg
PRESSURIZER TYPICAL DESIGN D A T A
Image by MIT OpenCourseWare.
Masche, G., System s Sum m a ry: W PW R NPP, 1971
Reactor Coolant Pumps
- Lar ge centrifugal pumps
- Utilize controlled leakage shaft seal
- H ave lar g e flywheel to ensure slow coast-down upon loss of electric power to the motor
PWR Secondary System
PWR STEAM GENER A T ORS
Primar y side , Hot ( T in = 324 ˚ C , T out = 288 ˚ C ) : Hi g h Pressure Li q uid Secondary side, Cold (T sat = 285 ˚ C): Lower Pressure Steam and Liquid
- Wa t e r Boils on Shell Side of Heat E x changer
- S team Passes through Liquid Separators, Steam Dryers
- L i q uid W a ter Naturall y Recirculates via Downcomer
- L evel Controlled via Steam and Feedwater Flowrates
U - T UBE STEAM G ENERAT O R
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Commons license. For more information, see http://ocw.mit.edu/fairuse . From : EPR bro chure. Avai l a bl e at www.areva.com
ONCE-THROUGH NUCLEAR STEAM GENERATOR
Used only in old B&W plants
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B&W , St eam, It s Generat i on & Use , 1972.
© Babcock & Wilcox. All rights reserved. This content is excluded from our Creativ e Commons license. For more information, see http://ocw.mit.edu/fairuse .
|
TYPICAL DESIGN DA T A FOR STEAM GENER A T ORS |
|||
|
Number and type |
4 V ertical, U-tube steam generators with integral steam-drum |
||
|
Height overall |
20.62 m |
||
|
Upper shell OD |
4.48 m |
||
|
Lower shell OD |
2.44 m |
||
|
Operating pressure, tube side |
15.5 MPa |
||
|
Design pressure, tube side |
17.2 MPa |
||
|
Design temperature, tube side |
343.3 o C |
||
|
Full load pressure, shell side |
6.90 MPa |
||
|
Maximum moisture at outlet (full load) |
0.25% |
||
|
Design pressure, shell side |
8.27 MPa |
||
|
Reactor coolant flow rate |
4360 kg/s |
||
|
Reactor coolant inlet temperature |
325.8 o C |
||
|
Reactor coolant outlet temperature |
291.8 o C |
||
|
Shell material |
Mn-Mo steel |
||
|
Channel head material |
Carbon steel clad internally with stainless steel |
||
|
T ube sheet material |
Mo-Cr -Ni steel clad with Inconel on primary face |
||
|
T ube material |
Inconel |
||
|
T ube OD |
2.22 cm |
||
|
A verage tube wall thickness |
1.27 mm |
||
|
Steam generator weights Dry weight, in place Normal operating weight, in place Flooded weight (cold) |
312,208 kg 376,028 kg 509,384 kg |
||
Image by MIT OpenCourseWare.
Masche, G., System s Sum m a ry: W PW R NPP, 1971
PWR p ower c y cle ( secondar y s y stem )
5 3
m • s
m • p
High
•
W T1
(1- f
) m •
g
Low
•
W T2
Reactor
Steam Generator
b a
Pressure T urbine
9
m • s
Moisture 11
Separato r
Pressure T urbine
4
7
6
2
Boiler 10
•
12
m • f
OFWH
f m • g
13
Condenser
8
1
Tu r b i n e
Feedwater
W P2 P ump
Main Condensate •
Pump W P1
Low Steam Pressure Requires: Lar g e turbine
Lower rotational speed (1800 RPM) Condenser
Steam Side at Low Pressure
Cooling water from sea, river or cooling tower
PWR safety systems and containment to be discussed later in the course
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22.06 Engineering of Nuclear Systems
Fall 20 10
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