Operational Reactor Safety

22.091 /22.903

Professor Andrew C. Kadak Professor of the Practice

Lecture 6 Reactor Energy Removal

Department of Nuclear Science & Engineering

Prof. Andrew C. Kadak, 2008 Page 1

Topics to Be Covered

• Power Distributions

• Peaking Factors

• Fuel-Pin Heat Transfer

• Nuclear Limits in Design

• Peak Centerline Temperature

• Peak Clad Temperature

• Departure From Nucleate Boiling

• Control Rod Impacts

Department of Nuclear Science & Engineering

Prof. Andrew C. Kadak, 2008 Page 2

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BWR Core Lattice

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“ B W R / 6: General Des c r iption of a BW R,” GE, 1980.

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PWR Fuel Assembly

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274 Nuclear Reactor S ysiems

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TOP NO ZZLE

CONTROL R00

BULGE J0IdT

Rod cv Guida Tube

FIGURE 1 0-6

Pr e ssuriz e d - wa tcr reactor ›’esscl. ( Courtesy of 1Vestin¿l›ouse Elcctric Corporation. )

Typical Four-Loop Reactor Core

Assemblies)

Cros s Sectio n (19 3 Fue l

Parameter s

Total heat output ~3250-3411 MWT

Heat gener ated in fuel 97.4%

Nominal s ystem pressure 2250 psia

Total coolant flow rate ~138.4 x 10 6 lb/hr Coolant Temper ature

Nominal inlet Average rise in vessel Outlet from vessel

557.5 ˚ F

61.0 ˚F

618.5 ˚ F

Equivalent core diameter 11.06 ft Core length, betwee n fuel ends 12.0 ft Fuel weight, uranium (first core) 86,270 kg Number of fu el assem blies 193

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Masche, G., Syst ems S u mmary: W PWR NPP, 1971

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Power Density

Department of Nuclear Science & Engineering

Prof. Andrew C. Kadak, 2008 Page 14

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Energy Removal

• Heat Balance in a reactor

– P ower Equation function of neutron flux

• Impact of Power Distribution on ability to remove heat and maintain temperature limits

– Material and Fuel limitations

Department of Nuclear Science & Engineering

Prof. Andrew C. Kadak, 2008 Page 15

Diffusion Theory Flux

Department of Nuclear Science & Engineering

Prof. Andrew C. Kadak, 2008 Page 16

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Flux Shapes

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Prof. Andrew C. Kadak, 2008 Page 17

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Power Peaking Factors

Department of Nuclear Science & Engineering

Prof. Andrew C. Kadak, 2008 Page 18

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Power Distributions

Department of Nuclear Science & Engineering

Prof. Andrew C. Kadak, 2008 Page 19

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Fuel Pin Cross Section

Department of Nuclear Science & Engineering

Prof. Andrew C. Kadak, 2008 Page 21

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Heat Removal Governing Processes

• Fuel Pin Power Production

– Conductive heat transfer

– F ourier Law of Heat Conduction

– P oisson’s Equation

• Clad Heat Transfer

– P oisson’s Equation but no heat source

• Clad to Coolant

– N ewton’s law of cooling

– C onvective Heat Transfer

• Gap to Clad

– C onvective

– Conductive heat tran sfer coefficient – hgap

Department of Nuclear Science & Engineering

Prof. Andrew C. Kadak, 2008 Page 22

Nuclear Limits

• Hot spot factor –

– P eak power in pin

– P revent Fuel Melting

• Hot Channel Factor

– A ssure heat removal from pin

– Minimum Departure from Nucleate Boiling Ratio

• Design Considerations

– Limits on Power

– M aterials

Department of Nuclear Science & Engineering

Prof. Andrew C. Kadak, 2008 Page 23

Department of Nuclear Science & Engineering

Prof. Andrew C. Kadak, 2008 Page 24

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Axial Peaking

Department of Nuclear Science & Engineering

Prof. Andrew C. Kadak, 2008 Page 25

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Control Rod Insertion

Rod “bite”

Department of Nuclear Science & Engineering

Prof. Andrew C. Kadak, 2008 Page 27

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Homework Assignment

Homework: Problems 7.2,5,6,8

Department of Nuclear Science & Engineering

Prof. Andrew C. Kadak, 2008 Page 28

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22.091 Nuclear Reactor Safety

Spring 200 8

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