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1

A Look at Nuclear Scienceand Technology

Larry Foulke

Module 6.3

Safety Systems and Plant Tour

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Nuclear Engineering Program

PWR Control Rod

Spider

Image Source: See Note 1

Full-Length Control Rods (inyellow) Mounted to Drives abovew/ Electromagnets

Fuel rods (in red) contain UO2pellets inserted into a Zircaloy-4tube

Spring clip grids provide supportfor the fuel rods in the fuelassembly

Top and bottom nozzles of the fuelassembly control the coolant flowdistribution and serve as structuralelements

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Nuclear Engineering Program

SCRAM / TRIP Full-Length Control Rods Mounted to Drives

w/ Electromagnets

Loss-of-Current Full Insertion

PWR Protective System

Trip / Protective Signals High Flux

High Temperature

High Pressure

Manual

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PWR (W)

Plant

Protection

System

Image Source: See Note 1

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Trip Signals

Redundancy

Interlocks for Power Changes

Reliability

Avoid Spurious Trips

Two-Out-of-Four Logic Same / Different Parameter

Consistent w/ Need for Repair

Fail-Safe Design

PWR Protective System

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Engineered Safety Features (ESFs)

Image Source: See Note 3

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Engineered Safety Features

Reactor Trip (RT) - 1st function

Control rods

Electromagnets / gravity insertion

Protective system / redundant sensors

Boric acid w/ emergency coolant injection

Rods alone may not shut core down on reflood

Boric acid concentration compensates for rodfailure

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Engineered Safety Features

Emergency core cooling (ECC) - 2ndfunction

Break location

Multiple loops

Distributed insertion points

Redundant / diverse

High-pressure injection (HPI) Low-pressure injection (LPI)

Accumulator

On-site / off-site power supplies

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Engineered Safety Features

Post-accident heat removal (PAHR) - 3rdfunction Large break - Initially cool ECCS water

Small break Forced circulation

Single-phase natural circulation

Two-phase natural circulation (reflux)

Feed and bleed HPI/LPI water into core

Steam discharged through Pzr PORV / safeties

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Engineered Safety Features

Post-accident radioactivity removal(PARR) - 4th function

Charcoal adsorbers for fission products

High-efficiency particulate air (HEPA) Filters

Reactive coatings for passive removal ofhalides

Containment water sprays

wash reactive products from atmosphere

Additives for pH control

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Nuclear Engineering Program

Engineered Safety Features

Containment integrity (CI) - 5th function

Isolation valves on containment buildingpenetrations

Automatic on overpressure signal

Main steam line valve design for quick close

Containment building

Inner leak-tight steel liner

Reinforced concrete shell

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Engineered Safety Features

Image Source: See Note 4

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PWR Engineered Safety Features

Image Source: See Note 3

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Engineered Safety Features (ESFs)

Image Source: See Note 3

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Safety Design Principles

Multiple barriers

Defense-in-depth

Protection / safety functions

Redundancy

Diversity

Physical separation

Fail-safe principle

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Safety Design Principles

Redundancy

More than minimum number of components

Design to tolerate component failure

Diversity

Protects against common-mode failure

Control rods and boric acid injection

Aux feed pumps - both electric and steam driven

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Safety Design Principles

Physical separation

Protects against simultaneous loss

Distance / physical barriers

Combination redundant / diverse / separated

Example: emergency electric power supply

Diesel generators

Multiple ties to off-site electrical grid Storage battery systems

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Nuclear Engineering Program

Safety Design Principles

Fail-safe principle

Components / systems automatically into safestcondition w/ failure or power loss

Examples: PWR rods - electromagnetic and gravity

BWR rods - solenoid / gas pressure

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1. Reprinted with permission from Westinghouse. Course:The Westinghouse Pressurized Water Reactor NuclearPower Plant (The Masche Book).

2. Reprinted with permission from Nuclear Engineering

International UK. Source: World Nuclear IndustryHandbook 2013

3. Adapted with permission from the American NuclearSociety. Nuclear Engineering Theory and Technology ofCommercial Nuclear Powerby Ronald Allen Knief, 2nd

Edition. Copyright 2008 by the American Nuclear Society,La Grange Park, Illinois. Figure 14-1 (slides 7 and 15) and14-2 (slide 14).

4. Reprinted with permission from Nuclear Energy Institute.http://www.nei.org/corporatesite/media/filefolder/containm

ent wall construction.jpg

Image Source Notes

http://www.nei.org/corporatesite/media/filefolder/containment_wall_construction.jpghttp://www.nei.org/corporatesite/media/filefolder/containment_wall_construction.jpghttp://www.nei.org/corporatesite/media/filefolder/containment_wall_construction.jpghttp://www.nei.org/corporatesite/media/filefolder/containment_wall_construction.jpg