ISO 4917-5:2024

International
Standard
ISO 4917-5
First edition
Design of nuclear power plants
2024-10
against seismic events —
Part 5:
Seismic instrumentation
Conception parasismique des installations nucléaires —
Partie 5: Instrumentation pour la détection et l'enregistrement
des séismes
Reference number
© ISO 2024
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Requirements for the seismic instrumentation . 2
4.1 General requirements .2
4.2 Instrument location .3
5 Instrumentation characteristics . 4
5.1 General requirements .4
5.2 Acceleration acquisition system .4
6 Actuation and alarms . . 6
7 Documentation . 7
Bibliography . 8

iii
Foreword
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iv
Introduction
Objective of the seismic instrumentation is to ascertain whether a seismic event has occurred at the site of
the nuclear power plant and to determine the size of this seismic event in relation to the one on which the
design of the plant was based.

v
International Standard ISO 4917-5:2024(en)
Design of nuclear power plants against seismic events —
Part 5:
Seismic instrumentation
1 Scope
This document specifies the utilization and characteristics of instrumentation used to detect seismic events
at nuclear power plants with water cooled reactors. The document can also be applied to other nuclear
facilities after verifying its applicability.
The following types of electrical systems and equipment are not covered by this document:
— seismic instrumentation involved in the implementation of nuclear safety functions as defined by
IEC 61226, for example automatic shutdown systems;
— seismic instrumentation not involved in the implementation of nuclear safety functions as defined by
IEC 61226 but which due, for example, to close proximity to other safety classified systems, requires
hardware qualification to be performed.
Such systems are specified, designed, manufactured, qualified, operated and dismantled according to the
relevant requirements of IEC standards, in particular IEC 61513 and the lower level IEC standards according
to the safety class and technologies used.
Seismic instrumentation used for the implementation of seismic reactor trip systems are developed
according to the requirements of IEC 63186.
An automatic shutdown system is not covered by this document.
This document specifies the requirements to be fulfilled by the seismic instrumentation such that, firstly,
it can be ascertained whether any of the design quantities on which the plant walk-down level and the
inspection levels are based have been exceeded and that, secondly, the recording of the time history of the
earthquake provides the necessary input values for a post-seismic analysis. The requirements are specified
such that, independent of the detection and recording system, comparable results within tolerances are
achieved in the time range as well as the frequency range.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 4917-1, Design of nuclear power plants against seismic events — Part 1: Principles
ISO 4917-6, Design of nuclear power plants against seismic events — Part 6: Post-seismic measures
IEC 61226, Nuclear power plants — Instrumentation, control and electrical power systems important to safety
— Categorization of functions and classification of systems
IEC/IEEE 60780-323, Nuclear facilities — Electrical equipment important to safety — Qualification
IEC/IEEE 60980-344, Nuclear facilities — Equipment important to safety — Seismic qualification

3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
acceleration sensor
sensor to detect the accelerations in three orthogonal directions and convert the accelerations into
transferable signals
3.2
acceleration acquisition system
system of different components that measures and records the absolute acceleration components as a
function of time
Note 1 to entry: The acceleration acquisition system essentially consists of several acceleration sensors (3.1), recording
devices (3.5) and seismic triggers (3.6), not necessarily located in one device.
3.3
aliasing effects
errors that occur, if a sampled signal contains frequencies higher than half of the sampling rate (Nyquist-
Frequency)
3.4
amplitude frequency response
frequency dependent relation between the real occurred and the instrumentally displayed amplitude of
acceleration
3.5
recording device
device that records measurement values as a function of time
3.6
trigger
electro-mechanical or logic device that initiates a corrective or protective action whenever a setpoint value
is crossed
Note 1 to entry: Lower and upper setpoints are common in numerous control systems, hence "exceeded" does not
apply in the literal sense.
3.7
setpoint
predetermined threshold value at which follow-up actions are initiated
4 Requirements for the seismic instrumentation
4.1 General requirements
The seismic instrumentation system being installed in the NPP is in general an individual I&C system part
of the overall I&C system of the NPP. The seismic instrumentation system shall be classified according to its
importance to safety. Classification shall be performed in accordance with the requirements of IEC 61226 or
other equivalent practices for NPPs.
The seismic instrumentation shall be seismically qualified for operability during and after a seismic event-
according to relevant IEC standards.

Concerning the qualification of the system, IEC/IEEE 60780-323 or equivalent requirements shall be applied,
in particular and specifically for seismic qualification IEC/IEEE 60980-344 or equivalent shall be applied.
The seismic instrumentation shall be provided with the objective of
a) detecting and quantifying the seismic effects at the plant site and at the power plant itself,
b) measuring the accelerations, recording the acceleration time histories and storing these data, and
c) enabling the comparison (of these data) with the design quantities basic to the design of the power plant.
It shall be ensured that, whenever trigger levels are exceeded, these are detected and displayed by the
seismic instrumentation for the plant inspections specified in ISO 4917-1.
NOTE 1 Plant inspections in buildings containing safety-related components are addressed in ISO 4917-6. The
definitions in ISO 4917-6 explain the relationship to OBE and SL-1 definitions.
It should be ensured that, immediately after a seismic event, it is determined and displayed whether the
criteria for the inspection level specified in ISO 4917-1 have been exceeded or have been significantly
exceeded for a shutdown level as specified in ISO 4917-6. This requires that, immediately after the recording
has ended, the recorded acceleration time histories, the resulting response spectra as well as a comparison
of the resulting response spectra with the ground response spectrum (free field response spectrum) or with
the analytic building response spectra are made available. Depending on national requirements, additional
elements such as CAV (Cumulative Absolute Velocity) can be defined.
The recorded acceleration time histories shall be appropriate for analytical verifications.
NOTE 2 Analytical verifications can be, for example, dynamic calculations or comparisons of spectra of safety-
related components and safety-related building structures.
4.2 Instrument location
Acceleration acquisition systems shall be provided at free field. Additional acquisition systems should be
installed inside the reactor building.
NOTE 1 The seismic design is based on the free field response spectrum. A comparison of the response spectrum
measured in the free field with the corresponding site-specific free field response spectrum (used for design) allows
to evaluate the whole power plant, because the reaction fo
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