Methodologies for Seismic Safety Evaluation of Existing Nuclear Installations

,

• Publisher: International Atomic Energy Agency
• Year: 2020
• ISBN:
  9789201060228
• Topic: Technologie et ingénierie
• Subtopic: Génie mécanique

Experience shows that an assessment of the seismic capacity of an existing operating facility can be required for a number of reasons, for example identification of potential seismic vulnerabilities based on operating experience events or the periodic safety review programme. This publication covers the seismic safety evaluation programmes to be performed on existing nuclear installations in order to ensure that the required fundamental safety functions are available, with particular attention to the safe shutdown of reactors. It includes lessons learned based on the IAEA Action Plan on Nuclear Safety following the Fukushima Daiichi accident, and updated methodologies for seismic safety evaluation of nuclear installations.

1. INTRODUCTION

1.1. Background

This Safety Report complements the guidance in IAEA Safety Standards Series No. NS-G-2.13, Evaluation of Seismic Safety for Existing Nuclear Installations [1], based on the IAEA experience feedback and involvement in seismic re-evaluations of nuclear power plants in Eastern Europe and lessons identified from the 2011 Fukushima Daiichi nuclear power plant accident.

Worldwide experience shows that an assessment of the seismic capacity of an existing operating facility can be necessary for a number of reasons, including the evidence of a greater seismic hazard at the site than expected before or a poor anti-seismic design in all or in part of the facility.

Post-construction evaluation programmes evaluate the current capability of the plant (i.e. the plant ‘as-is’) to withstand the seismic concern and identify any necessary upgrades or changes in operating procedures. Seismic qualification is distinguished from seismic evaluation primarily in that seismic qualification is intended to be performed at the design stage of a plant, whereas seismic evaluation is intended to be applied after a plant has been constructed and is operating or at the end of the design stage.

Seismic evaluation of existing nuclear installations differs from the practices applicable to the design of nuclear installations. The most prominent among these differences are:

(a) Plant condition: Paragraph 1.6 of NS-G-2.13 [1] states that “the seismic safety evaluation of existing installations strongly depends on the actual condition of the installation at the time the assessment is performed. This key condition is denoted the ‘as-is’ condition, indicating that an earthquake, when it occurs, affects the installation in its actual condition, and the response and capacity of the installation will depend on its actual physical and operating configuration. The as-is condition of the installation is the baseline for any seismic safety evaluation programme. The as-is condition includes the ‘as-built’, ‘as-operated’ and ‘as-maintained’ conditions of the installation, and its condition of ageing at the time of the assessment.”

(b) Evaluation criteria: The criteria used in the evaluation are different from those used in the design. Design tends to use the applicable loads to size the SSC to meet the limits set in the design code, while in evaluation the aim is to establish the capacity of the SSC in the ‘as-is’ condition and use it in the overall seismic evaluation of the installation. In doing this, experience from exposure to past seismic events, testing and analytical estimates of capacity are all utilized as sources of information. Thus, the process uses a significant level of expert judgement. The role played by the feedback of such experience, the associated practice of plant walkdowns and the qualification by experts are part of the evaluation methodologies discussed in this publication.

(c) Safety evaluation applicability: Seismic safety evaluations are used to assess the capacities of an installation when subject to beyond design basis seismic events. Seismic safety evaluation methodologies include probabilistic, deterministic and a combination of deterministic and probabilistic approaches.

A significant number of existing nuclear installations worldwide have undergone a seismic safety evaluation since the 1990s. Consequently, there is sufficient background experience supporting the seismic safety assessment methodologies presented in NS-G-2.13 [1] and detailed here. Seismic evaluation in the context of identification of vulnerabilities of nuclear power plants against external hazards is also addressed in Ref. [2].

1.2. Objective

This publication provides detailed guidance on conducting seismic safety evaluation programmes for existing nuclear installations in a manner consistent with NS-G-2.13 [1]. This publication can be used as a tool by regulatory organizations or other organizations responsible for the conduct of a seismic safety evaluation programme and provides a clear definition of the following:

— The objectives of the seismic evaluation programme;

— The phases, tasks and priorities in accordance with specific plant conditions;

— The common and integrated technical framework for establishing the acceptance criteria and its use in the seismic safety evaluation process.

1.3. Scope

The scope of this publication covers the seismic safety evaluation programmes to be performed on existing nuclear installations in order to ensure that the required fundamental safety functions are available, with particular application to the safe shutdown of reactors. Nuclear installations include: (i) land based, stationary nuclear power plants and research reactors; and (ii) nuclear fuel cycle facilities, including enrichment plants, processing plants, independent spent fuel storage facilities and reprocessing plants.

Seism...

Table of contents

• 1. INTRODUCTION
• REFERENCES
• DEFINITIONS
• ABBREVIATIONS
• CONTRIBUTORS TO DRAFTING AND REVIEW