ISO 16117:2013/PRF Amd 1

• Status: Not Published
• ICS: 27.120.20 - Nuclear power plants. Safety
• Technical Committee: ISO/TC 85/SC 5 - Nuclear installations, processes and technologies
• Drafting Committee: ISO/TC 85/SC 5 - Nuclear installations, processes and technologies
• Current Stage: 5020 - FDIS ballot initiated: 2 months. Proof sent to secretariat
• Start Date: 21-Sep-2026
• Completion Date: 26-Sep-2026

• Amends: ISO 16117:2013 - Nuclear criticality safety — Estimation of the number of fissions of a postulated criticality accident
• Effective Date: 17-Jun-2023

Overview

ISO 16117:2013/PRF Amd 1 is an ISO amendment focused on nuclear criticality safety and the estimation of the number of fissions of a postulated criticality accident. This amendment provides clarifications to the original document, helping users apply the standard more consistently in safety analysis and technical evaluation.

Published under the responsibility of ISO/TC 85/SC 5, the amendment is relevant to professionals working with nuclear installations, nuclear processes, and radiological protection. It supports clearer interpretation of assumptions, model applicability, and referenced estimation methods used in criticality accident analysis.

Key Topics

This amendment introduces practical clarifications that improve how the estimation approach is understood and applied:

• System assumptions for fission estimation

  • Materials involved in the system
  • Geometry of the system
  • Surrounding materials and their characteristics
  • Duration of the criticality accident
  • Degree of confinement and environmental conditions

• Additional estimation parameters

  • Total reactivity addition
  • Rate of reactivity addition

• Other factors of interest

  • For example, the time delay before the first persistent chain reaction in weak neutron source systems

• Simplified model applicability

  • A new sentence emphasizes that input data should be confirmed to fall within the range for which the simplified model is applicable

• Annex and bibliography updates

  • Annex D is updated to point users toward additional formulae and references
  • The bibliography includes new references related to simplified estimation methods and nuclear criticality slide rule updates

These clarifications strengthen the usability of the standard while preserving its role as a technical aid for criticality accident assessment.

Applications

ISO 16117:2013/PRF Amd 1 is useful in settings where professionals need reliable methods for estimating the number of fissions in a postulated criticality accident. Typical applications include:

• Nuclear criticality safety evaluations
• Safety case preparation
• Review of simplified estimation models
• Assessment of system configurations and accident scenarios
• Technical documentation and engineering analysis in nuclear facilities

The amendment is especially valuable when users need to interpret assumptions about geometry, materials, confinement, and accident duration. By clarifying these points, the document helps support more transparent and defensible criticality safety work.

Related Standards

This amendment is associated with the base standard:

• ISO 16117:2013 - Nuclear criticality safety - Estimation of the number of fissions of a postulated criticality accident

It is also part of the broader ISO work developed under:

• ISO/TC 85 - Nuclear energy, nuclear technologies and radiological protection
• ISO/TC 85/SC 5 - Nuclear installations, processes and technologies

For organizations tracking ISO nuclear criticality safety standards, this amendment serves as an important update for applying estimation methods with greater clarity and confidence.

International
Standard
ISO 16117
First edition
Nuclear criticality safety —
2013-10-01
Estimation of the number of fissions
of a postulated criticality accident
AMENDMENT 1
AMENDMENT 1
Sécurité de criticité nucléaire — Évaluation du nombre de
fissions en cas d'un hypothétique accident de criticité
AMENDEMENT 1
PROOF/ÉPREUVE
Reference number
ISO 16117:2013/Amd.1:2026(en) © ISO 2026

ISO 16117:2013/Amd.1:2026(en)
© ISO 2026
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
PROOF/ÉPREUVE
ii
ISO 16117:2013/Amd.1:2026(en)
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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization
...

ISO 16117:2013/PRF Amd. 1:2026(en)
ISO/TC 85/SC 5
Secretariat: BSI
Date: 2026-09-17xx
Amendment 1
2026-02-18
Nuclear criticality safety — Estimation of the number of fissions of a
postulated criticality accident
AMENDMENT 1: Clarifications
Nuclear criticality safety — Estimation of the number ofSécurité de criticité nucléaire — Évaluation du nombre
de fissions of a postulated criticalityen cas d'un hypothétique accident
de criticité
AMENDEMENT 1: Clarifications
PROOF
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication
may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying,
or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO
at the address below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel.Phone: + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent rights
in respect thereof. As of the date of publication of this document, ISO had not received notice of (a) patent(s)
which may be required to implement this document. However, implementers are cautioned that this may not
represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as i
...