Post on 24-May-2022
CANDU Chemistry –
An Introduction
Presented by D.A. Guzonas
Reactor Chemistry and Corrosion
Chalk River Laboratories
2009 October 29
Copyright: This document and the information contained in it is the property of Atomic Energy of Canada Limited (AECL). No use, disclosure, exploitation or transfer of any information contained
herein is permitted in the absence of an agreement with AECL, and the document may not be released without the written consent of AECL.
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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
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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
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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.
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CANDU 6 PLANT LAYOUT
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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
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Interface between NSSS and BOP
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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
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CANDU Nuclear Power Plant
Chemistry Control Issues
– Corrosion control for plant piping and components
– Reactivity control
– Safety
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CANDU Nuclear Steam Supply
System
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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
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Heat Transport System
CANDU 6
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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
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Moderator System and Auxiliaries
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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
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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
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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
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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
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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
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Balance of Plant: Turbine Building
CANDU 6 Steam Cycle
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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
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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
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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
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Chemistry Control Philosophy
CANDU Chemistry is a BALANCE:
– Engineering needs
– Materials integrity/chemistry requirements
– Production requirements
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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.
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