Design of the Reactor Core for Nuclear Power Plants

Specific Safety Guide

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• Publisher: International Atomic Energy Agency
• Year: 2019
• ISBN:
  9789201076229
• Topic: Technology & Engineering
• Subtopic: Mechanical Engineering
• Index: Technology & Engineering

The reactor core is the central part of a nuclear reactor where nuclear fission occurs. It consists of four basic systems and components: the fuel (including fuel rods and the fuel assembly structure), the coolant, the moderator and the control rods, as well as additional structures such as reactor pressure vessel internals, core support plates, and the lower and upper internal structure in light water reactors. This Safety Guide provides recommendations on meeting the safety requirements established in IAEA Safety Standards Series No. SSR-2/1 (Rev. 1), Safety of Nuclear Power Plants: Design, applied to the design of the reactor core for nuclear power plants. The publication addresses the safety aspects of the core design and includes neutronic, thermohydraulic, thermomechanical and structural mechanical aspects. Other aspects considered are those relating to reactor core control, shutdown and monitoring, and core management.

1. INTRODUCTION

Background

1.1. This Safety Guide provides recommendations on the design of the reactor core to meet the requirements established in IAEA Safety Standards Series No. SSR-2/1 (Rev. 1), Safety of Nuclear Power Plants: Design [1]. This publication is a revision of IAEA Safety Standards Series No. NS-G-1.121, which it supersedes.

Objective

1.2. The objective of this Safety Guide is to provide recommendations on meeting the safety requirements established in SSR-2/1 (Rev. 1) [1] for the design of the reactor core for nuclear power plants.

Scope

1.3. This Safety Guide is applicable primarily to land based stationary nuclear power plants with water cooled reactors for electricity generation or for other heat production (such as district heating or desalination). All recommendations are applicable to light water reactors (i.e. pressurized water reactors and boiling water reactors) and are generally applicable to pressurized heavy water reactors unless otherwise specified. This Safety Guide may also be applied, with judgement, to other reactor types (e.g. gas cooled reactors, floating reactors, small and modular reactors, innovative reactors) to contribute to the interpretation of the requirements that have to be considered in developing the design of the reactor core.

1.4. The reactor core is the central part of a nuclear reactor where nuclear fission occurs. The reactor core consists of four basic systems and components (i.e. the fuel (including fuel rods and the fuel assembly structure), the coolant, the moderator and the control rods), as well as additional structures (e.g. reactor pressure vessel internals, core support plates, and the lower and upper internal structure in light water reactors). This Safety Guide addresses the safety aspects of the core design and includes neutronic aspects, thermohydraulic aspects, thermomechanical aspects, structural mechanical aspects, aspects relating to reactor core control, shutdown and monitoring, and core management aspects for the safe design of the reactor core for nuclear power plants. Specifically, the following structures, systems and components (SSCs) are covered:

(a) Fuel rods, containing fuel pellets with or without burnable absorbers in cladding tubes, which generate and transfer heat to the coolant.

(b) Fuel assemblies, comprising bundles of fuel rods, along with structures and components (e.g. guide tubes, spacer grids, bottom and top nozzles, fuel channels) that maintain the fuel rods and fuel assemblies in a predetermined geometrical configuration.

(c) The reactor core control system, the shutdown system and the monitoring system, including components and equipment used for reactivity control and shutdown, comprising neutron absorbers (solid or liquid), the associated structure and the drive mechanism.

(d) Support structures that provide the foundation for the core within the reactor vessel (within the calandria for pressurized heavy water reactors), the structure for guiding the flow (for pressurized water reactors) and the guide tubes for reactivity control devices (for pressurized heavy water reactors).

(e) The coolant.

(f) The moderator.

(g) Other core components such as steam separators (for boiling water reactors) and neutron sources. These are considered only to a limited extent in this Safety Guide.

1.5. This Safety Guide is intended mainly for NPPs that use natural and enriched UO2 fuels and plutonium-blended UO2 fuel (mixed oxide fuel) with zirconium based alloy cladding. Unless otherwise specified, all recommendations apply to these fuel types.

1.6. For innovative fuel materials, such as uranium ­nitride fuel or inert matrix fuel, or cladding materials other than zirconium based alloys, this Safety Guide can be applied with judgement.

1.7. The design of the reactor core may interface with the design of other reactor systems and other related aspects. In this Safety Guide, recommendations on these interfacing systems and aspects are provided mainly to identify their functional interface. The relevant Safety Guides are referenced, as appropriate, in order to clarify the interfaces.

1.8. The terms used in this Safety Guide are to be understood as defined in the IAEA Safety Glossary [2]. Explanations of additional technical terminology are provided in Annex I.

Structure

1.9. Section 2 describes general considerations for safe core design based on requirements for the management of safety, principal technical requirements and general design requirements established in sections 3, 4 and 5 of SSR-2/1 (Rev. 1) [1], respectively. Section 3 describes specific considerations for the safe design of fuel rods, fuel assemblies, core structures and core components, and the core control system and the reactor shutdown system based on specific design requirements (i...

Table of contents

• 1. INTRODUCTION
• Annex ISUPPLEMENTARY TECHNICAL INFORMATION
• Annex II ASPECTS TO BE ADDRESSED IN THE DESIGN OF THE FUEL ROD, FUEL ASSEMBLY, REACTIVITY CONTROL ASSEMBLY, NEUTRON SOURCE ASSEMBLY AND HYDRAULIC PLUG ASSEMBLY
• CONTRIBUTORS TO DRAFTING AND REVIEW