Operational Reactor Safety

22.091 /22.903

Professor Andrew C. Kadak Professor of the Practice

Boiling Water Reactors Lecture 15

Topics to be Covered

• Steam Cycle

• Recirculation

• Chimney

• Steam separation

• Heat removal

• Operating with voids

• Plant systems

• Reactor Protective System

• Safety Systems

B W R Plan t Layou t

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BWR Plant Schematic

BWR Early

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Reactor Assembly

adak, 2008

Department of N

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Steam and Recirculation System

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Jet Pumps – Recirculation System

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Steam Separator and Dryer

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Key Systems of BWRs

• Standby Liquid Control System (SLCS)

– For redundant shutdown – c ontains boron

• Reactor Core Isolation Cooling System (RCIC)

– D eals with loss of feedwater flow

• Emergency Core Cooling System (ECCS)

– S afety Relief Valve – A utomatic Depressurization System

– H igh Pressure Coolant Injection System (HPCI)

– L ow Pressure Coolant Injection System (LPCI)

• Control Rod Drive System

– H ydraulic Control Units – from bottom of reactor vessel

• Residua l Hea t Remova l Syste m – deca y hea t remova l

Prof. Andrew C. Kadak, 2008

Department of Nuclea r S c ien ce & Engineering

Page 16

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ECCS

Department of Nuclea r S c ien ce & En

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ADS

ADS Valve

Department of Nuclea r S c ien ce & Engineering

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Reactor Power Control

• Control rods – g ross power changes

• Recirculation Flow - +/- 25 % power – Increase flow – i ncrease power

• Turbine Control – P ressure control - constant

– Generator demands more power – t urbine slows down – p ressure decreases – m ore steam created - increase turbine power –then increase recirculation flow to compensate for reactivity loss.

• Recall BWRs have negative void coefficient and Positive pressure coefficient

Reactor Trip Systems

• High Pressure in Drywell

• Low water level in reactor vessel

• High pressure in reactor vessel

• High neutron flux

• High water level in scram discharge volume (control rods)

• Closing of turbine stop or fast closure of turbine control valves

• Main steam line isolation

• High radiation levels in main steam lines

• Leak detection

• Lo w pressur e i n turbin e inle t

Trip Functions

• Insertion of control rods (hydraulic control units in bottom)

• Nuclear System Isolation

– R eactor Coolant Pressure Boundary

– C ontainment Isolation

– C losed System Isolation

Homework

• Read BWR handouts

• Problem 3.3 El Wakil

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22.091 Nuclear Reactor Safety

Spring 200 8

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