The Essential CANDU textbook cover with shadowy images behind

The Essential CANDU

The Essential CANDU is a peer-reviewed textbook on CANDU nuclear power technology. A resource that draws on expertise from many author and contributors from the CANDU profession and academia, it is ideally-suited for senior under-graduate and graduate students, educators and trainers as well as working professionals.

For readers new to CANDU, it will provide an opportunity to learn the basics of CANDU technology, including the overall system. More experienced users will also find it valuable due to the depth of specialized topics.

The Essential CANDU is an ideal resource, whether you are:

  • Considering a career in the nuclear industry
  • Looking for a university-level textbook or technical training resource for new employees, or
  • Need a reference resource to maintain and transfer workforce knowledge.

The Essential CANDU was a collaborative project between UNENE and the CANDU Owners Group. It was produced with the support and contributions from CANDU industry organizations including: Bruce Power, Canadian Nuclear Safety Commission, Canadian Nuclear Laboratories, Canadian Nuclear Society, Hydro Quebec, Kinectrics, Korea Hydro & Nuclear Power, New Brunswick Power, Ontario Power Generation, SNC-Lavalin, Societatae Nationala Nuclearelectrica (Romania), and Third Qinshan Nuclear Power Company (China). 

The textbook is available at or from the summary chapters below.

For more resources on CANDU, visit the UNENE Publications page on this website.

For more education opportunities, visit UNENE’s Education page to learn about the UNENE M.Eng program and other programs across the UNENE network of universities.

Table of Contents

Preface & Acknowledgements

Prologue – CANDU in Context

Chapter 1 – Introduction to Nuclear Reactors

Aerial view of Darlington Nuclear
Image: OPG

Dr. Robin Chaplin

This chapter provides a top-level introduction to nuclear reactors and surveys the world reactor situation. The various commercial large power producing reactors are identified and described against a brief background of nuclear reactor principles and key reactor components. The progressive expansion of nuclear power production is put into perspective in the global context. The operation of nuclear plants with respect to changing grid system demand is explained with some constraints identified. The chapter concludes with a brief review of safety and risk which are critical aspects in the design and operation of nuclear plants.

Chapter 2 – Genealogy of CANDU Reactors

NRX (National Research Experimental) Reactor nearing completion (1946)
Image: AECL

Dr. Robin Chaplin

This chapter discusses the historical beginnings and evolution of the CANDU reactor. The research and prototype reactors leading to the CANDU design are described with some of their principle technical parameters. Reasons for the choice of key parameters are given. This leads into a review of the evolution of the design of increasingly larger commercial CANDU reactors. The CANDU 6 reactor design has been chosen as a reference and a brief description of its main components with typical design parameters follows with a comparison with the CANDU 9 reactor. The chapter includes a note on the advantages of the CANDU reactor compared with other water-cooled reactors and a general review of reactor safety as applicable to most water-cooled reactors. It concludes with some technical details of the proposed Advanced CANDU reactor for comparison with existing commercial CANDU reactors.

Chapter 3 – Nuclear Processes and Neutron Physics

Diagram of nuclear fission
Image: Canadian Nuclear Association

Dr. Guy Marleau

In this chapter, the nucleus is first described, including its composition and the fundamental forces that affect its behaviour. Then, after introducing the concepts of radioactivity and nuclear decay, the various interactions between radiation and matter that can take place in and around a nuclear reactor, are discussed. The chapter finishes with a presentation of neutron physics for fission reactors.

Chapter 4 – Reactor Statics

Diagram of neutron flux
Image: University of Western Ontario

Dr. Benjamin Rouben, Dr. Eleodor Nichita

This chapter is devoted to the calculation of the neutron flux in a nuclear reactor under special steady-state conditions in which all parameters, including neutron flux, are constant in time. The main calculation method explored in this chapter is the neutron-diffusion equation. Analytical solutions are derived for simple neutron-diffusion problems in one neutron energy group in systems of simple geometry. Two-group diffusion theory and the approximate representation of the diffusion equation using finite differences applied to a discrete spatial mesh are introduced. The rudimentary reactor-physics design of CANDU reactors is presented. The two-step approach to neutronics calculations is presented: multi-group lattice transport calculations, followed by full-core, few-group diffusion calculations. Finally, the chapter covers fuel-property evolution with fuel burnup and specific features of CANDU neutronics resulting from on-line refuelling.

Chapter 5 – Reactor Dynamics

Diagram of CANDU Poison System
Image: CNSC

Dr. Eleodor Nichita, Dr. Benjamin Rouben

This chapter addresses the time-dependent behaviour of nuclear reactors. This chapter is concerned with short- and medium-time phenomena. Long-time phenomena are studied in the context of fuel and fuel cycles and are presented in Chapters 6 and 7. The chapter starts with an introduction to delayed neutrons because they play an important role in reactor dynamics. Subsequent sections present the time-dependent neutron-balance equation, starting with “point” kinetics and progressing to detailed space-energy-time methods. Effects of Xe and Sm “poisoning” are studied in Section 7, and feedback effects are presented in Section 8. Section 9 identifies and presents the specific features of CANDU reactors as they relate to kinetics and dynamics.

Chapter 6 – Thermal-Hydraulic Design

Rendering of typical CANDU reactor

Dr. Nikola K. Popov

This chapter covers the thermal-hydraulic design of nuclear power plants with a focus on the primary and secondary sides of the nuclear steam supply system. This chapter covers the following topics: evolution of the reactor thermal-hydraulic system; key design requirements for the heat transport system; thermal-hydraulic design principles and margins; design details of the primary and secondary heat transport systems; fundamentals of two-phase flow; fundamentals of heat transfer and fluid flow in the reactor heat transport system; other related topics.

Chapter 7 – Thermalhydraulic Analysis

Four cornerstone equations for the full two-fluid model with equal pressure

Dr. William J. Garland

This chapter is concerned with thermalhydraulic analysis of the process systems that are required to transport heat energy away from the nuclear reactor source and transform this heat energy into useful work (generally electrical energy. Thermal hydraulic system behaviour is largely determined by the simultaneous solution of the equations that govern the four variables (flow, pressure, density and enthalpy). The general mass, energy and momentum conservation equations are presented in general terms and are simplified to the common approximate forms used in systems modelling. The equation of state that is required for closure is explored with particular emphasis on implementation. Process system solution algorithms are investigated.

Chapter 8 – Nuclear Plant Systems

Reactor face at Bruce Power
Image: Bruce Power

Dr. Robin Chaplin

This chapter deals with the main components of a CANDU nuclear power plant. It follows the general path of energy production from the nuclear reactor to the electrical generator with descriptions of the systems and equipment essential for the purpose of generating thermal energy, transferring heat and converting heat into mechanical and then electrical energy. Some key auxiliary systems are included where these are an essential part of the energy processes as are the basic control systems which maintain stable operational conditions and ensure safety of the plant. This chapter leads into Chapter 9 which describes how a typical CANDU plant operates.

Chapter 9 – Nuclear Plant Operations

Nuclear plant control room
Image: SNN, Romania

Dr. Robin Chaplin

This chapter deals with the operating concepts of a CANDU nuclear power plant. It combines some theoretical aspects with basic operating procedures to explain how the plant operates. Key aspects related to plant control are addressed. Space allows only the primary energy generation, transport and conversion components to be covered, but there are many other components whose operation is vital for the efficient and safe operation of the plant. There is approximately an equal division of detail between the nuclear reactor, the heat transport and steam systems, and the steam turbine.

Chapter 10 – Instrumentation and Control

Control room with staff at Point Lepreau
Image: NB Power

Dr. G. Alan Hepburn

This chapter describes the role of instrumentation and control (I&C) in nuclear power plants, using the CANDU 6 design as an example. It is not a text on the general design of instrumentation and control algorithms, a subject which is well covered by many textbooks on the subject. Rather, it describes the architectural design of these systems in nuclear power plants, where the requirements for both safety and production reliability are quite demanding. The manner in which the instrumentation and control components of the various major subsystems co-operate to achieve control of the overall nuclear plant is described. The sensors and actuators which are unique to the nuclear application are also described, and some of the challenges facing designers of a future new build CANDU I&C system are indicated.

Chapter 11 – Electrical Systems

Worker with internal electrical systems
Image: OPG

Dr. Jin Jiang

This chapter covers grid requirements, station power systems and major electrical components in CANDU nuclear power plants (NPP). Grid requirements at an NPP location are discussed in terms of reliability and availability of off-site power, the need for a secure electricity supply for the electrical generation process, and the role of electricity in ensuring the safety of CANDU nuclear power plants. This four-part chapter also describes the operating principles of the major pieces of electrical equipment found in a CANDU plant.

Chapter 12 – Radiation Protection and Environmental Safety

Two people take water samples from a river
Image: CNL

Dr. Edward Waller

Crucial to operation of a CANDU nuclear plant is protection of workers, the public, and the environment. This chapter discusses:

  1. Basic fundamentals of radiation physics as they pertain to radiation interactions that have the potential to cause biological harm in living systems;
  2. Concepts of regulatory guidance which governs the “as low as reasonably achievable” radiation dose paradigm;
  3. Radiation detection and monitoring techniques used in CANDU plant environs.
  4. External and internal radiation hazards, including discussions on shielding and personal protective equipment;
  5. Radiation management plans, worker dose monitoring, and control and waste management issues; and
  6. Radiation releases to the environment, derived release limits, and environmental protection.

Chapter 13 – Reactor Safety Design and Safety Analysis

Worker inspects control panel
Image: OPG

Dr. Victor G. Snell

The chapter covers safety design and safety analysis of nuclear reactors. Topics include: concepts of risk, probability tools and techniques, safety criteria, design basis accidents, risk assessment, safety analysis, safety-system design, general safety policy and principles, and future trends. It makes heavy use of case studies of actual accidents both in provided text and exercises.

Chapter 14 – Nuclear Plant Materials and Corrosion

CANDU 6 feeder diagram
Image: IAEA

Dr. Derek H. Lister, Dr. William G. Cook

The choice of materials of construction of a nuclear reactor, while important in terms of plant capital cost, is crucial to the safe and economic operation of the unit throughout its design lifetime; it also affects decisions about plant life extension. This chapter describes the materials of construction of the main systems and components of a CANDU reactor and shows how they interact with their environments.

Most of the failures of nuclear systems involve the degradation of materials as they interact with their environments, indicating that chemistry control within systems should be formulated as materials are selected. The three major process systems of a CANDU reactor – the primary coolant, the moderator and the secondary coolant – have a variety of materials of construction, so the control of system chemistry in each is a compromise based on the characteristics of the interactions between the system materials and the environment, including the effects of irradiation on both the material and the coolant or moderator.

Chapter 15 – Chemistry in CANDU Process Systems

Workers perform maintenance on equipment
Image: OPG

Dr. William G. Cook, Dr. Derek H. Lister

The efficient and safe operation of a CANDU reactor is highly dependent upon the selection and proper implementation of chemistry control practices for the major and ancillary process systems such as the primary and secondary coolants and the moderator. The materials of construction of the various systems are selected in consideration of the neutron economy while keeping the proper chemical environment in mind to keep corrosion and degradation low and to ensure desired plant operating lifetimes. This chapter begins with an overview of the basic chemistry principles required to manage chemistry in CANDU reactors and then provides a detailed description of the chemistry control practices and the reasons behind their use in the major and ancillary process systems. The chapter concludes by examining the current practices of component and reactor lay-up for maintenance shutdowns and refurbishments and a description of heavy water purification and upgrading.

Chapter 16 – Regulatory Requirements and Licensing

Regulatory framework pyramid
Image: CNSC

Dr. Victor G. Snell, Dr. Nikola K. Popov

This chapter covers the overall aspects of nuclear reactor regulation (as of 2013), with emphasis on Canada, but also covering other regimes such as the United States, the United Kingdom and Europe. It explains the need for regulation; how regulators work; how they are structured; and the types of requirements they set. Canada, the United States and the United Kingdom are used as specific examples in these areas, with detailed material on Canadian licensing processes, requirements, and guides.

Chapter 17 – Fuel

CANDU 2 fuel bundle
Image: NWMO

Mukesh Tayal, Milan Gacesa

This chapter focuses on building a general understanding of the major mechanisms affecting fuel behaviour under normal operating conditions. Nuclear fuel, like conventional fuel, is responsible for generating heat and transferring the heat to a cooling medium. Unlike conventional fuel, nuclear fuel presents the additional challenge of retaining all the by-products of the heat-generating reaction within its matrix. Conventional fuel releases almost all its combustion by-products into the environment. Experience has shown that, at times, the integrity of CANDU fuel can be challenged while performing these roles.

Eighteen failure mechanisms have been identified, some of which cause fission by-products to be released out of the fuel matrix. CANDU reactors can locate and discharge fuel assemblies that release fission by-products into the coolant at power to minimize the effect of fuel defects on plant operation and the public. Acceptance criteria are established against which a fuel design is assessed to verify its ability to fulfill the design requirements without failing. A combination of analyses and tests is used to complete the verification assessments.

Chapter 18 – Fuel Cycles

Diagram of fuel cycle
Image: AECL

Mukesh Tayal, Milan Gacesa

Most commercial reactors currently use the once-through fuel cycle. However, because there is still a significant amount of useful material (and available energy) in the fuel discharged from these reactors, many fuel cycles are possible in which some fuel components are recycled for further reactor use. In addition, several other fuel cycles are also possible using thorium, which is much more abundant on Earth than the uranium that is the primary source of commercial nuclear power today.

The CANDU reactor is designed to use natural uranium fuel, which is less expensive and more efficient in the use of uranium than any known alternative. Some of the features that enable a CANDU reactor to operate on natural uranium also make it eminently capable of using alternative fuels.

Several alternative fuel and fuel cycles are described in this chapter, including the enriched uranium fuel cycle, the recovered-uranium cycle, the MOX cycle, the thorium cycle, the DUPIC cycle, the tandem cycle, low void reactivity fuel and actinide burning fuel.

Chapter 19 – Storage and Disposal of Irradiated Fuel

DGR diagram
Image: NWMO

Milan Gacesa, Mukesh Tayal

Nuclear wastes, in particular, irradiated nuclear fuel, must be handled, stored, and placed into permanent disposal facilities safely to prevent harm to people and the environment. Radioactive wastes can be grouped into four classes: (i) low-level radioactive waste, (ii) intermediate-level radioactive waste, (iii) high-level radioactive waste such as irradiated nuclear fuel, and (iv) uranium mine and mill waste. Storage and disposal of irradiated fuel in Canada follows a three-step process: storage in water-cooled pools, storage in air-cooled storage cylinders, and final disposal. The two stages of storage (the first two steps above) are fully proven and have been in practical operation for some time. The associated technical challenges that must be addressed and the engineered solutions are discussed in this chapter.

Several configurations for final disposal have been shown to be technically feasible. This chapter examines issues surrounding nuclear waste and disposal including public acceptance and implementation as well as ongoing work toward engineered disposal facilities.

Chapter 20 – Fuel Handling and Storage

Workers handle fuel bundle
Image: OPG

Diane Damario

CANDU reactors are fuelled on a somewhat continuous basis while on-power. This fuelling capability is mainly performed by two remotely operated fuelling machines. CANDU 6 fuelling machines are part of the fuel handling and storage system, which is divided into three main subsystems. New fuel transfer and storage involves the receipt, handling and storage of palletized crates of unirradiated, or new, fuel, the inspection and handling of individual new fuel bundles and the transfer of this fuel into a fuelling machine via a new fuel port.

Fuel changing involves a pair of fuelling machines transporting new fuel from a new fuel port to the reactor face, loading and unloading fuel from a reactor fuel channel and transporting discharged irradiated fuel from the reactor face to a spent fuel port. Spent fuel transfer and storage involves the discharge of irradiated fuel from a fuelling machine and the transfer and storage of this irradiated fuel in water-filled bays until the fuel is transferred to dry storage. This chapter examines all related aspects of fuel handling and storage.

Chapter 21 – CANDU In-core Fuel Management

Employees work on reactor at Point Lepreau
Image: NB Power

Dr. Benjamin Rouben

This chapter describes the physical and mathematical models and the computational methods used in the management of fuel in CANDU nuclear reactors. The concepts important to the topic of fuel management are explained: fuel irradiation (fluence), fuel burnup, cross-section averaging. The various levels of physics models used in fuel management are presented in quantitative detail: these are the continuous refuelling model, the time-average model, patterned-age snapshot models, and core-follow models.

The typical reactivity curve for the CANDU lattice is presented, and a method to estimate the average attainable fuel burnup from the reactivity curve is explained. The CANDU initial core and the first few months of operation are discussed. Finally, the chapter gives a short qualitative survey of advanced fuel cycles which could be exploited in CANDU reactors.

Author Biographies