ISO 12749-1:2020

INTERNATIONAL ISO
STANDARD 12749-1
First edition
2020-05
Nuclear energy — Vocabulary —
Part 1:
General terminology
Énergie nucléaire — Vocabulaire —
Partie 1: Terminologie générale
Reference number
©
ISO 2020
© ISO 2020
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ii © ISO 2020 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
3.1 Basic terms related to nuclear energy, nuclear technologies, and radiological protection . 1
3.2 Terms related to nuclear energy . 3
3.3 Terms related to safety . 4
3.4 Terms related to measurement . 6
3.5 Terms related to radioactive waste management and decommissioning . 9
Annex A (informative) Methodology used in the development of the vocabulary .11
Bibliography .17
Alphabetical index .18
Foreword
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This document was prepared by Technical Committee ISO/TC 85, Nuclear energy, nuclear technologies,
and radiological protection.
A list of all parts in the ISO 12749 series can be found on the ISO website.
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iv © ISO 2020 – All rights reserved

Introduction
This document provides terms and definitions for basic concepts of nuclear energy, nuclear technologies,
and radiological protection. Terminological data are taken from ISO standards developed by ISO/TC 85
and other technically validated documents, including the IAEA Glossary and vocabularies issued by
different organizations Organization for Economic Co-operation and Development, Nuclear Energy
Agency, Joint Committee for Guides in Metrology.
Unambiguous communication of nuclear energy and radiological concepts is crucial taking into account
the relevant implications that may arise from misunderstandings with regard to equipment and
materials involved in the standards dealing with these activities. In line with the international demand
for harmonization of terminology regarding nuclear and radiological activities, this standard will
contribute to provide general, cross-cutting terms and definitions to meet users´ requirements. It will
also improve promotion, knowledge and use of international standards dealing with nuclear energy,
nuclear technologies and radiological protection and will help experts developing technical standards
to avoid overlapping and contradiction.
Arrangement of terms and definitions is based on concepts systems that show corresponding
relationships among nuclear and radiological concepts. Such arrangement provides users with a
structured view of the nuclear energy, nuclear technologies, and radiological protection sectors and will
facilitate common understanding of all related concepts, see also Annex A. Besides, concepts systems
and conceptual arrangement of terminological data will be helpful to any kind of user because it will
promote clear, accurate and useful communication in fields like basic and applied sciences, technology,
industry, health, safety, security and human resources training.
INTERNATIONAL STANDARD ISO 12749-1:2020(E)
Nuclear energy — Vocabulary —
Part 1:
General terminology
1 Scope
This document contains the terms, definitions, notes to entry and examples corresponding to the basic
concepts of the nuclear energy, nuclear technologies, and radiological protection subject fields.
It provides the minimum essential information for each cross-cutting concept represented by a
single term.
NOTE A full understanding of concepts goes with a background knowledge of nuclear energy, nuclear
technologies, and radiological protection. It is intended to facilitate communication and promote common
understanding.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at http:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1 Basic terms related to nuclear energy, nuclear technologies, and radiological
protection
3.1.1
radioactivity
stochastic process whereby nuclei undergo spontaneous disintegration, usually accompanied by the
emission of subatomic particles, or photons
[SOURCE: IAEA Safety Glossary, 2018 Revision, June 2019, modified by adding “stochastic natural” at
the beginning of the sentence, by replacing “atoms” with “nuclei”, by deleting “usually” and by replacing
“radiation” with “subatomic particles, and/or photons”.]
3.1.2
activity
A
quotient of −dN by dt, where dN is the change in the number of radioactive nuclei, at a particular energy
state and at a given time, due to spontaneous nuclear transformations in the time interval dt
[SOURCE: ICRU 85, 6.2, October 2011, modified by changing the order of the phrases, by deleting the
word “mean”, by adding the word “radioactive”.]
Note 1 to entry: It is expressed as AN=−dd/ t . Activity can be calculated as AN=λ , where λ is the decay constant
(3.1.11) and N is the number of present radioactive nuclei.
Note 2 to entry: The special name for the unit of activity in the International System of Units is Becquerel (Bq),
−1 10
where 1 Bq = 1 s . The use of the former unit Curie (1 Ci = 3,7 × 10 Bq), is also accepted in many countries and
in BIPM.
3.1.3
radiation
emission or transmission of energy in the form of waves or particles through space or through a
material medium
Note 1 to entry: The term also applies to the radiated energy itself. Radiation includes electromagnetic, acoustic
and particle radiation, as well as all forms of ionizing radiation.
[SOURCE: science.wolfram.com retrieved 5 December 2017, modified.]
3.1.4
ionizing radiation
radiation (3.1.3) capable of displacing electrons from atoms or molecules, thereby producing ions
Note 1 to entry: Ionizing radiation includes alpha radiation, beta radiation, neutron radiation, gamma or x rays,
and cosmic rays.
[SOURCE: NCRP Composite Glossary
https:// ncrponline .org/ wp -content/ themes/ ncrp/ PDFs/ NCRP -Composite -Glossary .pdf]
3.1.5
radiation source
apparatus, substance or installation, that may cause radiation exposure, by emitting ionizing radiation
(3.1.4) or releasing radioactive substances or materials
[SOURCE: ISO 12749-2:2013, 1.1.1 modified — by deleting the word “anything” and parenthesis to fulfil
terminological requirement with regard to drafting of definitions.]
3.1.6
radiation processing
intentional irradiation of products or materials to preserve, modify or improve their characteristics
[SOURCE: ISO/ASTM 52628:2013, 3.1.12]
3.1.7
radiation shield
shielding
material interposed between a source of radiation (3.1.3) and persons, equipment or other objects, in
order to attenuate the radiation
[SOURCE: ISO 12749-5:2018, 3.1.20, modified — by changing the verb “attenuate” by “reduce”.]
3.1.8
radionuclide
nuclide which is in an unstable state due to excess of internal energy and which will attain a stable state
by emitting radiation (3.1.3)
40 235 238 232
Note 1 to entry: Radionuclides are either naturally occurring, such as K, U, U, Th and their radioactive
decay (3.1.10) products, or produced by activation or other artificial means.
3.1.9
half-life
T
1/2
mean time taken for the activity of an amount of radionuclide (3.1.8) to become half its initial value
Note 1 to entry: T ln2/λ, where λ is the decay constant (3.1.11).
1/2 =
2 © ISO 2020 – All rights reserved

3.1.10
decay
spontaneous nuclear transformation of one nuclide into a different nuclide or into a
different energy state of the same nuclide
[SOURCE: NCRP Composite Glossary
https:// ncrponline .org/ wp -content/ themes/ ncrp/ PDFs/ NCRP -Composite -Glossary .pdf]
3.1.11
decay constant
λ
quotient of dP by dt, for a radionuclide in a particular energy state, where dP is the likelihood of a single
nucleus undergoing a spontaneous nuclear transition from that energy state in the time interval dt
dP 1 dN
λ = =-
dt N dt
where N is the number of nuclei of concern existing at time t and A is the activity (3.1.2)
Note 1 to entry: The decay constant is related to the radioactive half-life (3.1.9), T , of the radionuclide by the
1/2
ln2
expression: λ =
T
12/
[SOURCE: IAEA Safety Glossary, 2018 Revision, June 2019, modified — by changing the position of the
phrase between commas to fulfil terminological requirement with regard to drafting of definitions.]
3.2 Terms related to nuclear energy
3.2.1
nuclear energy
energy released by nuclear fission (3.2.2) or fusion
3.2.2
nuclear fission
splitting of a nucleus into fission fragments, either spontaneously or as a result of the impact of a
particle, usually with an associated release of energy
Note 1 to entry: The nucleus usually has a high mass number, together with an intermediate or low average-
binding-energy-per-nucleon; hence, an inherent instability exists, and the fission fragments are usually highly
unstable.
[SOURCE: ISO 12749-5:2018, 3.1.1]
3.2.3
nuclear fusion
reaction in which two atomic nuclei combine to form a heavier atomic nucleus with the release of energy
[SOURCE: “Collins Dictionary”. 2019 (Retrieved: November 06, 2019)]
2 3
Note 1 to entry: Nuclear fusion occurs with very light element nuclei, like H, He, etc.
3.2.4
chain reaction
self-sustaining reaction in which the fission of nuclei of one generation of nuclei produces particles that
cause the fission of at least an equal number of nuclei of the succeeding generation
3.2.5
nuclear fuel
fissionable nuclear material in the form
...