CANDU Chemistry An Introduction

CANDU Chemistry –

An Introduction

Presented by D.A. Guzonas

Reactor Chemistry and Corrosion

Chalk River Laboratories

2009 October 29

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CANDU Chemistry –

An Introduction

Lecture 1: Introduction to CANDU Systems Chemistry

Lecture 2: Corrosion of Materials

Lecture 3: Chemistry Fundamentals

Lecture 4: Chemistry In the PHTS

Lecture 5: Moderator and Auxiliary Systems Chemistry

Lecture 6: Other Core Systems Chemistry

Lecture 7: Chemistry Around the Steam Cycle

Lecture 8: Service Water and Miscellaneous Systems


Course Objectives

By the end of this course you should:

– Understand the rationale for chemistry

control in major CANDU plant systems

– Understand the major chemistry and

corrosion issues in CANDU plants


The CANDU 6 as Illustration

In this course, the CANDU 6 design is used for illustration

Same principles/philosophy apply to all

CANDU plants, including the ACR

And to NRU, etc.


CANDU 6 PLANT LAYOUT


Rationale for Chemistry Control

Chemistry

Control

Materials

Selection

Corrosion Product and

Activity Transport

Decontamination

and Cleaning

Easy to implement,

low cost

Hard to implement,

expensive

Increased Inspections

and Maintenance

Repair of Degraded

Components

Degradation


Interface between NSSS and BOP


CANDU Nuclear Power Plant

Reactor Core

– Natural uranium fuel

– Horizontal fuel channels

– On-power fuelling

– Heavy water coolant and heavy water moderator

– Supplies heat to generate steam

Balance of Plant

– Recirculating, vertical steam generators

– Light water for secondary coolant to transfer heat (as steam) to the turbine/generator to produce electricity

– Service water systems provide cooling for plant heat exchangers


CANDU Nuclear Power Plant

Chemistry Control Issues

– Corrosion control for plant piping and components

– Reactivity control

– Safety


CANDU Nuclear Steam Supply

System


Nuclear Steam Supply System

Heat Transport System (HTS)

– Remove fission heat and transfer that heat to

steam generator to produce steam

– Cool fuel during normal and abnormal operating

conditions, e.g., reactor shutdown, loss of power to

heat transport pumps

– Steam generators transfer heat from HTS system

via steam to the turbine generator set


Heat Transport System

CANDU 6


Nuclear Steam Supply System

Moderator System

– Slow high energy fission neutrons to thermal

energy to promote further nuclear fission

– Control reactivity using chemical poisons during

normal operation and shutdown

– Provide backup heat sink following severe

accident, e.g., loss-of-coolant (LOCA)

– Moderator temperature maintained at ~70°C by

removing heat generated as a result of:

– Moderation and adsorption of gamma rays

– Heat transfer from pressure tubes


Moderator System and Auxiliaries


Other Auxiliary Systems in the NSSS

End Shield Cooling System

– Removes heat from end (biological) shields

Spent Fuel Bay

– Store spent fuel, remove decay heat, protect

personnel from radiation

Liquid Zone Control System

– Provides zone and short-term reactivity control

Annulus Gas System

– Provides thermal barrier between calandria and

pressure tube, and provides early warning for leak

detection


Safety-Related Systems

Dousing System

– Limits reactor building pressure peak following

loss-of-coolant accident (LOCA)

Emergency Core Cooling System

– Removes residual and decay heat from reactor

core following a LOCA

Liquid Injection Shutdown System

– Injects soluble neutron poison to maintain reactor

in guaranteed shutdown condition


CANDU Steam Cycle

Steam Generators transfer heat from HTS and

produce steam

High Pressure (HP) and Low Pressure (LP) turbines

–Series of bladed wheels set in motion by jets of steam

–Convert internal energy of steam into mechanical energy of

rotation

–Moisture Separator Reheater

– Removes liquid from HP turbine exhaust

– Superheat steam to the LP turbines


CANDU Steam Cycle

Condenser

– Shell-and-tube design with cooling water on inside of

the tubes

– Condensed steam is collected in hotwell

– Deaeration of condensate


CANDU Steam Cycle

HP and LP Feedwater Heaters

– Shell-and-tube U-tube heaters used to raise feedwater

temperature on inside of the tubes

– Shell-side heated by steam from HP and LP turbines

Deaerator and Storage Tank

– Heats condensate by direct contact with steam

– Removes gases (i.e., O2) and vents to atmosphere

– Stores water for boiler feed pumps in storage tank

– Tank holds 5 full-power minutes of main steam flow


Balance of Plant: Turbine Building

CANDU 6 Steam Cycle


Balance of Plant:

Pumphouse/Powerhouse

Provides station water for:

– Condenser cooling (CCW)

– Open loop; river, lake, sea-water

– Recirculated cooling water (RCW)

– Closed loop; demineralised water

– Raw service water (RSW)

– Open loop; river, lake, sea-water

– Emergency water service (EWS)

– Fire protection, portable water, demineralised

water


Balance of Plant:

Pumphouse/Powerhouse

Power Production

– Moderator cooling

– End-shield coolers

– HTS and BF pump cooling

– Turbine and seal oil coolers

– Local building air coolers

Nuclear Safety

– Cooling for normal reactor shutdown

– Removal of decay heat

– Cooling under accident conditions, i.e., LOCA, seismic event


Chemistry Control Philosophy

Design:

– Set chemistry regime during design process

– Select materials appropriately

Operation:

– Monitor and control chemistry to ensure adequate

protection of diverse materials


Chemistry Control Philosophy

CANDU Chemistry is a BALANCE:

– Engineering needs

– Materials integrity/chemistry requirements

– Production requirements


Reference Documents

Chemistry Control Design Guide for Pressurized Heavy Water

CANDU Reactors, 95-03081-DM-01.

Heat Transport System Chemistry Control; 95-01200-CDR-001.

Steam-Cycle Chemistry Control; 95-01200-CDR-002.

Chemistry Control for Service Water Systems; 95-01200-CDR-003

Chemistry Control for Moderator and Auxiliaries Including Liquid

Injection Shutdown System; 95-01200-CDR-004.

Reactor Auxiliary Systems Chemistry Control–Part I; 95-01200-

CDR-005.

Reactor Auxiliary Systems Chemistry Control–Part II; 95-01200-

CDR-006.

Recommended CANDU Sampling Design and Practices, 95-01200-

200-008.
