ISO 12749-5:2018
(Main)Nuclear energy, nuclear technologies, and radiological protection — Vocabulary — Part 5: Nuclear reactors
Nuclear energy, nuclear technologies, and radiological protection — Vocabulary — Part 5: Nuclear reactors
ISO 12749-5:2018 encompasses the collection of terms, definitions, notes and examples corresponding to nuclear reactors, excluding quantitative data. It provides the minimum essential information for each nuclear reactor concept represented by a single term. Full understanding of concepts requires background knowledge of the nuclear field. It is intended to facilitate communication and promote common understanding. The scope of ISO 12749-5:2018 covers the whole field of nuclear reactors at a broad surface level.
Énergie nucléaire, technologies nucléaires, et radioprotection — Vocabulaire — Partie 5: Réacteurs nucléaires
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Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 12749-5
First edition
2018-02
Nuclear energy, nuclear technologies,
and radiological protection —
Vocabulary —
Part 5:
Nuclear reactors
Énergie nucléaire, technologies nucléaires, et radioprotection —
Vocabulaire —
Partie 5: Réacteurs nucléaires
Reference number
©
ISO 2018
© ISO 2018
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ii © ISO 2018 – All rights reserved
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
Annex A (informative) Methodology used in the development of the vocabulary .34
Bibliography .46
Alphabetical index .47
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
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on the ISO list of patent declarations received (see www .iso .org/ patents).
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URL: www .iso .org/ iso/ foreword .html.
This document was prepared by ISO/TC 85, Nuclear energy, nuclear technologies, and radiological
protection.
A list of all the parts in the ISO 12749 series can be found on the ISO website.
iv © ISO 2018 – All rights reserved
Introduction
This document provides terms and definitions for main concepts in the whole area of nuclear reactor
science, technology, engineering, projects and operations, excluding quantitative data. Terminological
data are taken from ISO standards developed by TC 85/SC 6, from other technically validated documents
issued by international organizations, especially IAEA and IEC, while a number of definitions have been
drafted by WG 1 experts on the basis of their experience and after detailed discussions on concept
characteristics, the best wording for their designations and definitions, as well as the most important
links between concepts.
In most cases, international consensus exists among the communities of nuclear reactor specialists
world-wide, on the most relevant concepts in the nuclear reactor area. Nevertheless, clear and
unambiguous terms for these concepts are also needed.
The foregoing needs also to be considered together with the fact that a large number of people are
involved in the broad nuclear reactor area, having different scopes and levels of scientific and
technical knowledge and frequently having very specific activities within that broad field. Thus,
there can be different understandings and assumptions about concepts. Hence, the result could be a
poor communication that might lead into unexpected, different risky situations or consequences, if a
conceptual difference is behind.
Conceptual arrangement of terms and definitions is based on concepts systems that show corresponding
relationships among nuclear reactors concepts. Such arrangement provides users with a structured
view of the nuclear energy sector and will facilitate common understanding of all related concepts.
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.
Structure of the vocabulary
The terminology entries are presented in the conceptual order of the English preferred terms. Both
a systematic index and an alphabetical index are included at the end of the standard. The structure
of each entry is in accordance with ISO 10241-1. See also Annex A for the methodology used in the
development of the vocabulary.
All the terms included in this document deal exclusively with nuclear reactor technology. When selecting
terms and definitions, special care has been taken to include the terms that need to be defined, that is
to say, either because the definitions are essential to the correct understanding of the corresponding
concepts or because some specific ambiguities need to be addressed. The notes appended to certain
definitions offer clarification or examples to facilitate understanding of the concepts described.
According to the title, the vocabulary deals with concepts belonging to the general nuclear energy field
within which concepts in the nuclear reactors sub-field are taken into account.
Looking for an easier presentation of the required large number of defined concepts, the content of this
document has been split into nine headings as shown below, which makes easier any search of terms or
relationships between concepts.
vi © ISO 2018 – All rights reserved
INTERNATIONAL STANDARD ISO 12749-5:2018(E)
Nuclear energy, nuclear technologies, and radiological
protection — Vocabulary —
Part 5:
Nuclear reactors
1 Scope
This document encompasses the collection of terms, definitions, notes and examples corresponding
to nuclear reactors, excluding quantitative data. It provides the minimum essential information for
each nuclear reactor concept represented by a single term. Full understanding of concepts requires
background knowledge of the nuclear field. It is intended to facilitate communication and promote
common understanding.
The scope of this document covers the whole field of nuclear reactors at a broad surface level.
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 https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1 General terms related to nuclear reactors
3.1.1
nuclear fission
process by which a nucleus undergoes a partition in two, infrequently in three, main fission fragments,
releasing energy
Note 1 to entry: There are two types of nuclear fission: “spontaneous” and “induced” ones.
Note 2 to entry: The nucleus usually has a high mass number A, together with an intermediate or low average-
binding-energy-per-nucleon; hence, an inherent instability exists, and the fission fragments are usually highly
unstable.
Note 3 to entry: According to their capability for undergoing fission, a nucleus and its associated nuclide can be
qualified as fissionable or eventually fissile.
3.1.1.1
induced nuclear fission
nuclear fission (3.1.1) initiated by a nucleus when an external colliding particle is absorbed
Note 1 to entry: The absorption of the external colliding particle, usually a neutron, generates a strong increase
in the compound nucleus internal energy and, hence, increases the compound nucleus instability, favouring a
large energy release by means of a nucleus partition.
3.1.1.2
spontaneous nuclear fission
nuclear fission (3.1.1) produced in a nucleus, having an inherent instability, that develops itself in a
purely stochastic way and without intervention of any external colliding particle
3.1.2
fissionable nuclide
nuclide capable of undergoing fission by interaction with a neutron of some energy
Note 1 to entry: The definition may be restricted to significant capability, e.g. to a nuclide that is capable of
supporting a self-sustaining nuclear chain reaction (3.1.9).
3.1.3
prompt fission neutron
neutron released out from a fission fragment in a stochastic way, with high kinetic-energy just following
initiation of a nuclear fission (3.1.1) process
Note 1 to entry: The number of prompt neutrons released per fission, is stochastic as indicated, with an average
value in the range 2,5 to 3 for most of concerned nuclides.
Note 2 to entry: Prompt fission neutron kinetic-energies form a continuum, between 0 and around 10 MeV, for a
population of prompt fission neutrons released, with an average value usually close to 2 MeV.
3.1.4
prompt fission radiation
gamma and/or beta radiations released in a stochastic way, out from each decaying fission fragment
just following initiation of a nuclear fission (3.1.1)
Note 1 to entry: These gamma and beta radiations are released in cascades, reflecting the high internal energy
level of most of fission fragments just after fission initiation.
3.1.5
fission product
nuclide produced from nuclear fission (3.1.1) or from subsequent radioactive decay of such a nuclide
[SOURCE: ISO 12749-3:2015, 3.1.5]
3.1.5.1
fast neutron
neutron with kinetic energy greater than its surroundings when released during fission
3.1.5.1.1
delayed fission neutron
neutron emitted in few particular fission product (3.1.5) decays, typically with half-lives roughly in the
range 0,1 s to 1 min, following initiation of a nuclear fission (3.1.1)
Note 1 to entry: Such decay occurs between two energy levels of a fission product-namely precursor-favouring
a neutron release, hence, the emitted neutron will have a quite defined kinetic-energy at its release, typically
below 1 MeV.
Note 2 to entry: In a fission neutron population, since delayed neutrons have kinetic evolutions dictated by those
rather long periods, as compared to the extremely fast evolutions of prompt neutrons, the first ones provide an
important contribution to the kinetic control of that neutron population.
3.1.5.1.1.1
thermal neutron
neutron that has, by collision with other particles, reached an energy state equal to that of its
surroundings
Note 1 to entry: on the order of 0,025 eV (electron volts).
[SOURCE: United States Nuclear Regulatory Commission Glossary (Retrieved: 8 August 2017) https://
www .nrc .gov/ reading -rm/ basic -ref/ glossary .html], modified.
2 © ISO 2018 – All rights reserved
3.1.5.2
delayed fission radiation
gamma and/or beta, in certain cases also alpha radiations released in a stochastic way, from a
radioactive fission product (3.1.5)
Note 1 to entry: Every possible fission product decay has extremely diverse half-lives, covering the range around
0.1 s up to more than a billion years.
Note 2 to entry: These “delayed” released gamma, beta and alpha radiations, after interactions with neighbouring
atoms, are mainly absorbed by the surrounding materials and then finally converted into heat: they are the
source of what is designated as decay-power or decay-heat or residual-heat.
3.1.6
fissile nuclide
nuclide capable of undergoing fission by interaction with neutrons
[SOURCE: ISO 12749-3:2015, 3.1.2]
3.1.7
fertile nuclide
nuclide that after absorbing a neutron becomes a fissile nuclide (3.1.6)
238 239 240
Note 1 to entry: In practice, the main fertile nuclides are: U (producing the fissile Pu), Pu (producing the
241 232 233
fissile Pu) and Th (producing the fissile U), in all cases after the absorption of one neutron and the fast
emission of
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