ISO 1709:1995

INTERNATIONAL
STANDARD
Second edition
1995-l l-01
Nuclear energy - Fissile materials -
Principles of criticality safety in storing,
handling and processing
hergie nucl6aire - Ma t&es fissiles - Principes de s&urit& en mat&e
de criticit lors du stockage, de la manipulation et du traitemen t
Reference number
IS0 1709:1995(E)

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IS0 1709:1995(E)
Foreword
IS0 (the International Organization for Standardization) is a worldwide
federation of national standards bodies (IS0 member bodies). The work
of preparing International Standards is normally carried out through IS0
technical committees. Each member body interested in a subject for
which a technical committee has been established has the right to be rep-
resented on that committee. International organizations, governmental
and non-governmental, in liaison with ISO, also take part in the work. IS0
collaborates closely with the International Electrotechnical Commission
(I EC) on all matters of electrotechnical standardization.
Draft International Standards adopted by the technical committees are cir-
culated to the member bodies for voting. Publication as an International
Standard requires approval by at least 75 % of the member bodies casting
a vote.
International Standard IS0 1709 was prepared by Technical Committee
lSO/TC 85, Nuclear energy, Subcommittee SC 5, Nuclear fuel technology.
This second edition cancels and replaces the first edition (IS0 1709: 1975),
which has been technically revised.
0 IS0 1995
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced
or utilized in any form or by any means, electronic or mechanical, including photocopying and
microfilm, without permission in writing from the publisher.
International Organization for Standardization
Case postale 56 l CH-1211 Geneve 20 l Switzerland
Printed in Switzerland

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INTERNATIONAL STANDARD @ IS0 IS0 1709:1995(E)
Fissile materials - Principles of
Nuclear energy -
criticality safety in storing, handling and processing
IS0 7753: 1987, Performance requirements and
1 Scope
testing procedures for criticality detection and alarm
systems.
This International Standard specifies the basic prin-
ciples and limitations which govern operations with
fissile materials. It discusses general criticality safety
criteria for equipment design and for the develop-
3 Procedures
ment of operating controls, while providing guidance
for the assessment of procedures, equipment, and
3.1 General
operations. It does not cover quality assurance re-
quirements or details of equipment or operational
The early recognition of the special hazards associ-
procedures, nor does it cover the effects of radiation
ated with fissile materials has led to the application of
on man or materials, or sources of such radiation,
formal control practices based on principles of criti-
either natural or as the result of nuclear chain reac-
cality safety. Diligent and conscientious application of
tions. Transport of fissile materials outside the
these principles has produced an accident record
boundaries of nuclear establishments is not within
which compares favorably with the frequency and
the scope of this International Standard and should
severity of common industrial accidents. Continuation
be governed by appropriate national and international
and improvement of this generally favorable record
standards and regulations.
requires the cooperation of all those involved in op-
erations.
These criteria apply to operations with fissile materials
outside nuclear reactors but within the boundaries of
nuclear establishments. They are concerned with the
limitations which must be imposed on operations
3.2 Responsibility
because of the unique properties of these materials
which permit them to support nuclear chain reactions.
Operational responsibility for criticality safety shall be
These principles apply to quantities of fissile materials
clearly defined and shall belong to operations manage-
in which nuclear criticality can be established.
ment throughout the normal chain of command.
3.3 Equipment design
2 Normative reference
Safety shall, to a practicable extent, be taken into
The following standard contains provisions which,
account when designing operating equipment, for
through reference in this text, constitute provisions of
example, by restrictions on vessel geometry. The
this International Standard. At the time of publication,
early incorporation of criticality safety considerations
the edition indicated was valid. All standards are
into plant design facilitates design and provides
subject to revision, and parties to agreements based
economic benefits. Process and equipment design
on this International Standard are encouraged to
may require approval by the appropriate authority.
investigate the possibility of applying the most recent
edition of the standard indicated below. Members of
Processing controls may be enhanced by the use of
IEC and IS0 maintain registers of currently valid
appropriate instrumentation.
International Standards.
1

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@ IS0
IS0 1709:1995(E)
be mixed with or located near fissile materials. The
3.4 Criticality assessment
achievement of criticality depends upon
The criticality assessment shall consider all reasonably
foreseen abnormal conditions. Processing supervision
a) the nuclear properties of the fissile material;
shall assist in determining such abnormal conditions.
b) the mass of fissile material present and its
The process shall be required to remain subcritical
distribution within the system being assessed;
with an appropriate margin under such conditions, but
it should be recognized that, in the event of unfore-
c) the mass and distribution of all other materials
seen circumstances, additional assessment may be
associated with the fissile material.
required before attempting to recover from the
situation.
The assessment should consider all processing con-
ditions that can be foreseen as reasonable.
3.5 Written procedures
4.2 Methods of control
Written procedures shall govern all operations involv-
ing fissile material in excess of those threshold quan-
Methods of control of criticality safety in any oper-
tities defined by management. Copies of applicable
ation include, but are not limited to, any one or a
written procedures should be posted up or available in
combination of the following:
operating areas.
a) limitation of the dimensions or shape of
operational equipment;
3.6 Review of procedures
b) control of the mass of fissile material presen t in
The assessment of criticality aspects of written
an operation;
procedures shall be performed by persons skilled in
the interpretation of experimentally validated criticality
control of the concentration of fissile materia I in
d
data and familiar with criticality safety practices and
solutions;
processing operations. These persons should, to a
d) control of neutron moderation associated with
practicable extent, be administratively independent of
the fissile material;
operations.
e) the presence of appropriate neutron absorbers;
reliance on neutron absorbers requires assurance
3.7 Processing violations
of their continued presence;
Processing violations and unusual occurrences shall
f) control of the spacing between material and
be reported, analised, and considered for possible
equipment.
improvements in criticality safety practices.
3.8 Training
4.3 Achievement of control
Training of processing operators shall include criticality
The control of criticality safety by such methods as
safety. The extent of training shall provide
...