ISO 23466:2020

Design criteria for the thermal insulation of reactor coolant system main equipments and piping of PWR nuclear power plants

This document specifies the basic requirements of thermal insulation design of reactor coolant system (RCS) equipment and piping. Among thermal insulation of various RCS equipment and piping, the following two kinds of thermal insulations are described in detailed based on common design logic and requirements: — thermal insulation of reactor pressure vessel (RPV); — thermal insulation of RCS piping and other equipment. This document is valid for two types of thermal insulation: — metallic thermal insulation; — non-metallic thermal insulation. This document mainly applies to nuclear power plants with pressurized water reactor (PWR). For other reactor types, this document can be taken as reference.

Critères de conception du calorifuge des composants primaires principaux et des tuyauteries du circuit primaire principal des centrales nucléaires REP

General Information

• Status: Published
• Publication Date: 21-Oct-2020
• ICS: 27.120.20 - Nuclear power plants. Safety
• Technical Committee: ISO/TC 85/SC 6 - Reactor technology
• Drafting Committee: ISO/TC 85/SC 6/WG 3 - Power reactor, siting, design, construction, operation, and decommissioning
• Current Stage: 6060 - International Standard published
• Start Date: 22-Oct-2020
• Due Date: 11-Jul-2021
• Completion Date: 22-Oct-2020

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 23466
First edition
2020-10
Design criteria for the thermal
insulation of reactor coolant system
main equipments and piping of PWR
nuclear power plants
Critères de conception du calorifuge des composants primaires
principaux et des tuyauteries du circuit primaire principal des
centrales nucléaires REP
Reference number
ISO 23466:2020(E)
©
ISO 2020

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ISO 23466:2020(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2020
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
ii © ISO 2020 – All rights reserved

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ISO 23466:2020(E)

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 General design procedure. 2
4.1 General requirements . 2
4.2 Reactor safety considerations . 2
4.3 Material selection . 3
4.3.1 General requirements . 3
4.3.2 Primary insulating material . 3
4.3.3 Outer cladding/encapsulating material . 4
4.3.4 Support/fixation material . 4
4.4 Design and test of thermal behaviour . 4
4.4.1 Design of thermal behaviour . 4
4.4.2 Test of thermal behaviour . 6
4.5 Design and test of mechanical properties . 6
4.5.1 Design of mechanical properties . 6
4.5.2 Test of mechanical properties . 7
4.6 Additional requirements . 8
5 Design requirements of RPV thermal insulation . 9
5.1 General requirements . 9
5.2 Safety requirements . 9
5.3 Material selection . 9
5.4 Thermal behaviour requirements .10
5.5 Mechanical properties and structural requirements .10
6 Design requirements of thermal insulation of RCS piping and other equipment .10
6.1 General requirements .10
6.2 Safety requirements .10
6.3 Material selection .11
6.4 Thermal behaviour requirements .11
6.5 Mechanical properties and structural requirements .11
Annex A (informative) Geometry description of metallic thermal insulation .13
Annex B (informative) Geometry description of non-metallic thermal insulation .15
Annex C (informative) Type of RPV thermal insulation with RPV external cooling safety
functionality .18
Annex D (informative) Type of RPV thermal insulation with radiation shield safety
functionality .21
Bibliography .24
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ISO 23466:2020(E)

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
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on 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 (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www .iso .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 85, Nuclear energy, nuclear technologies,
and radiological protection, Subcommittee SC 6, Reactor Technology.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2020 – All rights reserved

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INTERNATIONAL STANDARD ISO 23466:2020(E)
Design criteria for the thermal insulation of reactor
coolant system main equipments and piping of PWR
nuclear power plants
1 Scope
This document specifies the basic requirements of thermal insulation design of reactor coolant system
(RCS) equipment and piping.
Among thermal insulation of various RCS equipment and piping, the following two kinds of thermal
insulations are described in detailed based on common design logic and requirements:
— thermal insulation of reactor pressure vessel (RPV);
— thermal insulation of RCS piping and other equipment.
This document is valid for two types of thermal insulation:
— metallic thermal insulation;
— non-metallic thermal insulation.
This document mainly applies to nuclear power plants with pressurized water reactor (PWR). For other
reactor types, this document can be taken as reference.
2 Normative references
The following standards 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 standards (including any amendments) applies.
ISO 7345, Thermal performance of buildings and building components — Physical quantities and definitions
ISO 9229, Thermal insulation — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 7345, ISO 9229 and the
following 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
metallic thermal insulation
thermal insulation with metallic material as the primary insulating material
Note 1 to entry: The metallic thermal insulation is composed by large number of thermal insulation panels. Each
thermal insulation panel is surrounded by outer cladding and filled by inner metallic reflective foils/sheets. The
geometry of inner packed foils/sheets can be embossed structure or liners in parallel.
Note 2 to entry: The typical geometry of metallic thermal insulation is shown in Annex A. The geometry
mentioned in Annex A can be referred by designers.
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ISO 23466:2020(E)

3.2
non-metallic thermal insulation
thermal insulation with non-metallic material as the primary insulating material
Note 1 to entry: Geometry of non-metallic thermal insulation can be divided into three categories:
— Thermal insulation composed by large number of thermal insulation panels. Each thermal insulation panel is
surrounded by outer cladding and filled by inner non-metallic insulating material.
— Layers of non-metallic insulating thermal insulation materials strapped together.
— Thermal insulation mattresses (composed by non-metallic insulating material wrapped in fibre clothing).
Note 2 to entry: The typical geometry of non-metallic thermal insulation is shown in Annex B. The geometry
mentioned in Annex B can be referred by designers.
3.3
chimney effect
air circulation between the inner and outer side of thermal insulation originating from heat source
EXAMPLE If clearance and extensive heat exchange paths exist between thermal insulation and the
insulated equipment/piping, external cold air would continuously enter from the lower part due to the density
and pressure difference between inside and outside of the thermal insulation. The incoming airflow will be
heated and thus travels upward to the top of thermal insulation and eventually exits from the upper part.
3.4
thermal bridge
channel with extremely large heat flow due to direct connection between inner/outer surface of thermal
insulation and the material with great heat conductivity of the insulated structure
4 General design procedure
4.1 General requirements
The design procedures of thermal insulation shall be comprehensively considered to fulfil all
functionalities. The safety class, quality assurance classification and seismic category requirements,
which are specified by equipment specification or other relevant documents, shall be satisfied. The
design of thermal insulation should take into account the following processes:
— reactor safety considerations;
— material selection;
— design and test of thermal behaviour;
— design and test of mechanical properties, including seismic and vibration resistance, etc.
In addition, other requirements about installation, removing, maintenance, in-service inspection and
replacement shall also be considered during the design process of thermal insulation.
4.2 Reactor safety considerations
The design of thermal insulation shall meet the safety requirements specified in the local regulations,
codes and standards where the product is manufactured and used. Thermal insulation shall be
carefully selected, and its application shall guarantee the fulfilment of its safety functionalities and to
minimize interference with other safety functionalities in the event of thermal insulation deteriorating.
Meanwhile, the safety requirements of RCS components shall also be considered and specified in the
data sheets of thermal insulation.
As a design output of thermal insulation and a design input of safety facilities, the debris source caused
by thermal insulation in the event of breaking shall not affect the normal operation of the emergency
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ISO 23466:2020(E)

core cooling system (ECCS), pit strainer and other safety facilities. Quantity and granulometry of debris
shall be considered. This consideration applies to the whole thermal insulation system rather than a
single local thermal insulation.
For thermal insulation areas where workers may get in contact with or get close to, the outer surface
temperature of thermal insulation shall be limited to guarantee human safety.
For thermal insulation, which belong to a nuclear safety related class or provide reactor safety
functionalities, the following requirements can be selectively implemented in the design of thermal
insulation to meet the functional requirements of the safety system. For thermal insulation, which
belong to non-nuclear safety class, the following requirements are not mandatory.
— Under normal service condition or anticipated events, thermal insulation shall withstand
corresponding loads and perform all the functionalities during design lifetime.
— Under seismic conditions, thermal insulation shall have its impact on the insulated and adjacent
components minimized.
— If any safety functionality needs to be performed by thermal insulation itself, reliable realization of
such functionalities shall be ensured.
4.3 Material selection
4.3.1 General requirements
Thermal insulation materials shall meet the reactor safety requirements specified in the local
regulations, codes and standards where the product is manufactured and used. Debris source caused
by the material itself shall meet relevant requirements given in 4.2.
Thermal insulation materials mainly include primary insulating material, outer cladding/encapsulating
material, support/fixation material, etc. Radiation induced material performance degradation over its
design lifetime shall be considered during material selection. The maximum service temperature of
all materials shall be higher than the design or operating temperature of the insulated equipment and
piping. The maximum service temperature shall have appropriate margins.
4.3.2 Primary insulating material
The primary insulating material will have a direct impact on the safety requirement, thermal
behaviour, mechanical properties and geometry of the thermal insulation. Therefore, selection of
primary insulating material may be carried out firstly. The primary insulating material can be one of
the following two types:
a) metallic insulating material;
b) non-metallic insulating material.
As per the classification of primary insulating material, types of thermal insulation should also be
classified as metallic and non-metallic thermal insulation.
Metallic insulating material achieves its functionality by virtue of the suppressed heat radiation due
to low surface emissivity. Thus, surface brightened metallic material with low surface emissivity may
be selected. Austenitic stainless steel is recommended. If the risk of potential hydrogen production
and its impact on reactor safety are evaluated and measurements are capable to control the hydrogen
concentration under limit, aluminum and galvanized steel are also applicable.
Metallic insulating material shall meet requirements given in relevant standards with regard to
chemical composition and properties (including mechanical properties, physical properties and
corrosion-resistant properties, etc.), and have good processing performance.
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ISO 23466:2020(E)

Non-metallic insulating material achieves its functionality by virtue of the suppressed heat
convection due to the porous interior structure. Materials such as fibre, microporous material, etc. are
recommended.
Non-metallic insulating material and the products made by the non-metallic insulating material shall
have good radiation resistance. Such resistance should be validated by irradiation test. No obvious
embrittlement, pulverization, contraction and thermal conductivity increasing shall occur over the
design lifetime.
Over its design lifetime, non-metallic insulating material shall also be able to resist steam, moisture,
fungi, disintegration and fire under service conditions.
Any noxious or harmful effect (formaldehyde emission, carcinogenicity and other possible harmful
factors) caused by the non-metallic material shall be limited in accordance with the local regulations,
codes and standards where the product is manufactured and used. Strict control of organic binder shall
be imposed for non-metallic materials.
For equipment and piping insulated and contacted directly with non-metallic insulation, the tendency
of stress corrosion cracking shall be evaluated. No mass production is allowed unless this tendency is
proved to be trivial. For non-metallic insulating material applied for austenitic steel components, the
level of leachable chloride, fluoride, sodium and silicate ions as well as pH value of leached water shall
be strictly limited.
4.3.3 Outer cladding/encapsulating material
The outer cladding/encapsulating material is used for manufacturing the cladding shell, encapsulating
panel or other outer protective parts for the primary insulating material. During the design lifetime,
the material shall have enough strength to withstand loads acting on the cladding/encapsulating
parts. In order to satisfy sealing requirement under different service conditions, processes including
riveting, fillet welding, intermittent welding, and seal welding can be adopted for the cladding shell
and encapsulating panel assembling. If the outer cladding/encapsulating material is different from
the primary insulating material or the adjacent equipment/piping material in contact, the influence of
corrosion and other negative tendency caused by the contact between different types of materials shall
be evaluated and the tendency shall be proved to be trivial before mass production.
4.3.4 Support/fixation material
The support/fixation material is used for manufacturing support frame, support leg, strap or other
parts for supporting and fixing the thermal insulation. During the design lifetime, the material shall
have enough strength to withstand loads acting on the support/fixation parts. If the support/fixation
material is different from the primary insulating material or the adjacent equipment/piping material
in contact, the influence of corrosion and other negative tendency caused by the contact between
different types of materials shall be evaluated and the tendency shall be proved to be trivial before
mass production.
4.4 Design and test of thermal behaviour
4.4.1 Design of thermal behaviour
In the design of thermal behaviour, the surface temperature or heat productivity of insulated equipment
and piping may be considered as the design input, the heat loss limit of insulated equipment and piping
may be set as design objective. This heat loss limit is generally specified in the equipment specification
or other corresponding documents and mainly described by the following parameters:
— heat flux of thermal insulation outer surface;
— temperature of thermal insulation outer surface;
— heat loss of thermal insulation.
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ISO 23466:2020(E)

After the above design input and objective are provided and specified, the design thickness of thermal
insulation shall be determined by theoretical method. Calculation of the design thickness is based on
Formula (1) or Formula (2). Formula (1) applies to the calculation under heat transfer through flat wall,
while Formula (2) applies to the calculation under heat transfer through cylinder wall. Also, Formula (3)
gives the calculation method of heat flux from heat loss. The design thickness of the insulation can then
be determined. Formula (3) can also be used to verify the heat flux calculation result by checking the
compatibility with heat loss limit.
The thermal conductivity coefficient λ in Formula (1) and Formula (2) can be obtained from standards
or heat transmission test described in 4.4.2. For the heat transfer coefficient, h, both heat convection
transfer coefficient, h , and heat radiation transfer coefficient, h , of the thermal insulation outer surface
c r
shall be taken into account, as shown in Formula (4). Appropriate safety margin shall be considered for
the design thickness.
It shall be noted that the calculated design thickness is the net thickness of the primary insulating
material, excluding outer cladding, encapsulating or any other material without thermal insulating
functionality.
The following formulae are only applicable to basic theoretical calculation. Other methods with
corrected/optimized factors or empirical formulae are also allowed depending on the actual design and
application conditions of the thermal insulation.
δ 1
 
qT=Δ / + (1)
 
λ h
 
dd 
1
oo
qT=Δ /l×+n (2)
 
2λ dh
 
i
Qq=×A (3)
hh=+ h (4)
cr
where
q is the heat flux of thermal insulation;
ΔT is the temperature difference between inner and outer surfaces of thermal insulation;
λ is the thermal conductivity coefficient of thermal insulation;
δ is the design thickness of thermal insulation under heat transfer through flat wall;
d is the design outer diameter of thermal insulation under heat transfer through cylinder wall;
o
d is the design inner diameter of thermal insulation under heat transfer through cylinder wall;
i
h is the heat transfer coefficient of thermal insulation outer surface;
h is the heat convection transfer coefficient of thermal insulation outer surface;
c
h is the heat radiation transfer coefficient of thermal insulation outer surface;
r
Q is the heat loss of thermal insulation;
A is the heat transfer area of thermal insulation.
The shape and the direction of the thermal insulation, the ambient temperature and the ventilation
condition should all be considered when calculating the heat convection transfer coefficient of outer
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ISO 23466:2020(E)

surface. The different calculation methods can be adopted based on certainty conditions. The heat
radiation transfer coefficient shall be consistent with the primary insulating material properties.
In addition, thermal expansion induced displacement of thermal insulation and insulated equipment
and piping should be considered, expansion and contraction during start-up and shutdown of the
reactor should also be considered. Obvious effects of the functionalities of typical insulation parts due
to thermal stress or deformation shall be verified by corresponding analyses.
Calculation only by theoretical formulae is acceptable if the geometry and heat transfer conditions
are simple. If various heat transfer influence factors exists or the shape of insulation is complex
and irregular, finite element method or other verified equivalent analysis method should be used to
calculate the heat flux, temperature distribution and heat loss.
If the heat exchange paths between inner and outer side of thermal insulation are unavoidable, chimney
effect shall be accounted for thermal behaviour prediction.
For factors hard to model or quantify (e.g. ventilation and chimney effect), conservative assumption
regarding such factors should be considered to ensure the analysis results are enveloped with sufficient
confidence.
4.4.2 Test of thermal behaviour
After the primary insulating material has been selected, the thermal conductivity coefficient should
be obtained by heat transmission test. This heat transmission test can be performed on the material
itself or on typical thermal insulation panel. In order to obtain the thermal conductivity coefficient as
close to the actual in-service condition as possible, the unidirectional heat transmission test for typical
thermal insulation panel is preferred.
Heat transmission test with simulated actual service condition can be performed before thermal
insulation design is finalized for suppliers involved in the design of thermal insulation for the first time.
Such a test should also be performed if a new geometry, a new material or a new process is introduced
without previous experiences for the mass production. Heat transfer calculation results for thermal
behaviour design can be validated by such a test.
Main factors (including hot surface temperature, ambient temperature, nearby ventilation condition,
etc.) that effect the heat transfer behaviour of the thermal insulation should be simulated in this test.
The geometry, material and manufacturing process of the heat transmission test specimens shall be
representative of the actual products.
4.5 Design and test of mechanical properties
4.5.1 Design of mechanical properties
In the design of mechanical properties of thermal insulation, the loads under different design conditions
may be considered as design input, the fulfilment of different functionalities or structural integrity
requirement under various conditions may be set as design objective.
The design input includes, but not limited to, the following loads:
— the mass of the thermal insulation and its accessories;
— the loads due to thermal expansion and contraction of the thermal insulation itself;
— the loads due to vibration;
— the loads due to seismic condition and other external hazards (if any);
— the loads caused by other adjacent equipment interfaced with the thermal insulation (if any);
— the loads due to pre-service inspection (if any);
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ISO 23466:2020(E)

— the loads due to the thermal expansion and contraction of insulated equipment and piping (if any);
— additional loads caused by safety functionalities performed by the thermal insulation itself (if
...

DRAFT INTERNATIONAL STANDARD
ISO/DIS 23466
ISO/TC 85/SC 6 Secretariat: DIN
Voting begins on: Voting terminates on:
2019-12-18 2020-03-11
Design criteria for the thermal insulation of reactor
coolant system main equipments and piping of PWR
nuclear power plants
ICS: 27.120.20
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
This document is circulated as received from the committee secretariat.
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
ISO/DIS 23466:2019(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
©
PROVIDE SUPPORTING DOCUMENTATION. ISO 2019

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ISO/DIS 23466:2019(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2019
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]
Fax: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved

---------------------- Page: 2 ----------------------
ISO/DIS 23466:2019(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 General design procedure. 2
4.1 General requirements . 2
4.2 Requirements for reactor safety . 2
4.3 Material selection . 3
4.3.1 General requirements . 3
4.3.2 Main insulating material . 3
4.3.3 Outer cladding/sealing material . 4
4.3.4 Support/fixation material . 4
4.4 Thermal behaviourr design and test . 4
4.4.1 Thermal behaviourr design . 4
4.4.2 Thermal behaviourr test . 6
4.5 Mechanical properties design and test . 6
4.5.1 Mechanical properties design . 6
4.5.2 Mechanical properties test . 7
4.6 Other requirements . 8
5 Design requirement of thermal insulation of RPV . 8
5.1 General requirement . 8
5.2 Safety requirement . 9
5.3 Material selection . 9
5.4 Thermal behaviour requirement . 9
5.5 Mechanical properties and structure requirement .10
6 Design requirement of thermal insulation of RCS piping and other equipment .10
6.1 General requirement .10
6.2 Safety requirement .10
6.3 Material selection .11
6.4 Thermal behaviour requirement .11
6.5 Mechanical properties and structure requirement .11
Annex A (informative) Structure description of metallic thermal insulation .13
Annex B (informative) Structure description of non-metallic thermal insulation.16
Annex C (informative) A kind of RPV thermal insulation bearing RPV external cooling
safety function.19
Annex D (informative) A kind of RPV thermal insulation bearing radiation shield safety
function .22
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ISO/DIS 23466:2019(E)

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
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on 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 (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www .iso .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 85, Nuclear energy, nuclear technologies,
and radiological protection, Subcommittee SC 6, Reactor Technology.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2019 – All rights reserved

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ISO/DIS 23466:2019(E)

Introduction
For PWR nuclear power plants, the function of thermal insulation of reactor coolant system (RCS)
equipment and piping is to reduce heat loss, improve ambient condition, reduce thermal stress of RCS
equipment and piping and guarantee the normal operation of reactor.
The purpose of this document is to provide internationally uniform design principle and method for
thermal insulation of RCS equipment and piping in PWR nuclear power plant, which mainly contains
the thermal behaviour, material selection, structural design, and test method requirements.
For thermal insulation which belongs to nuclear safety related class or category, or performing reactor
safety related function, the corresponding design requirements are also offered in this document.
Among thermal insulation of various RCS equipment and piping, the following two kinds of thermal
insulations would be detailed described on the basis of some common design logic and requirements:
— thermal insulation of reactor pressure vessel (RPV)
— thermal insulation of RCS piping and other equipment
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DRAFT INTERNATIONAL STANDARD ISO/DIS 23466:2019(E)
Design criteria for the thermal insulation of reactor
coolant system main equipments and piping of PWR
nuclear power plants
1 Scope
This document specifies the basic requirements related to the design of thermal insulation of reactor
coolant system (RCS) equipment and piping.
This document is valid for two types of thermal insulation.
— metallic thermal insulation
— non-metallic thermal insulation
This document mainly applies to pressure water reactor (PWR) nuclear power plants. For other reactor
types, this document can be taken as reference.
2 Normative references
The following standards 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 standards (including any amendments) applies.
ISO 7345, Thermal performance of buildings and building components — Physical quantities and definitions
ISO 8302, Thermal insulation — Determination of steady-state thermal resistance and related properties —
Guarded hot plate apparatus
ISO 8497, Thermal insulation — Determination of steady-state thermal transmission properties of thermal
insulation for circular pipes
ISO 8990, Thermal insulation — Determination of steady-state thermal transmission properties —
Calibrated and guarded hot box
ISO 9229, Thermal insulation — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 7345, ISO 9229 and the
following 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
metallic thermal insulation
thermal insulation with metallic material as main insulating material
Note 1 to entry: The metallic thermal insulation is composed by amounts of thermal insulation panels. Single
thermal insulation panel consists of outer cladding and inner packed metallic reflective foils/sheets. The
geometry of inner packed foils/sheets can be embossed or parallel liners.
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ISO/DIS 23466:2019(E)

Note 2 to entry: The detailed description of typical geometry of metallic thermal insulation is shown in Annex A.
The geometry mentioned in Annex A can be taken as reference for designer.
3.2
non-metallic thermal insulation
thermal insulation with non-metallic material as main insulating material
Note 1 to entry: Geometry of non-metallic thermal insulation can be divided into three kinds:
— Thermal insulation composed by amounts of thermal insulation panels. Single thermal insulation panel
consists of outer cladding and inner packed non-metallic insulating material.
— Thermal insulation strapped layer by layer with non-metallic insulating material.
— Thermal insulation matresses (non-metallic insulation material stuffed in fiber cloth).
Note 2 to entry: The detailed description of typical geometry of non-metallic thermal insulation is shown in
Annex B. The geometry mentioned in Annex B can be taken as reference for designer.
3.3
chimney effect
air circulation between inside and outside of thermal insulation derived by heat source
EXAMPLE If any gap was existed between thermal insulation and equipment or piping insulated, meanwhile
amounts of heat exchange paths were existed in most part of thermal insulation, thermal pressure or density
difference would be formed between the inner and outer side of thermal insulation. Initiated by this difference,
the cold air would enter the inside through the lower gaps, move upward and be heated, finally escape to the
outside through the top gaps.
3.4
thermal bridge
path with high heat flow, caused by geometry with high thermal conductivity material connecting the
inner and outer surface of thermal insulation directly
4 General design procedure
4.1 General requirements
All requirements for thermal insulation function realization shall be comprehensively considered
in the design procedure of thermal insulation. The safety class, quality assurance classification and
seismic category requirements, which are specified by equipment specification or other corresponding
documents, shall be satisfied. The design of thermal insulation can be performed as following
subsequence:
— Consideration of requirements about reactor safety
— Material selection
— Thermal behavior design and test
— Mechanical properties design and test, including seismic resistance, vibration resistance, etc.
Besides, other requirements including installation, remove, maintenance, in-service inspection and
replacement shall also be considered in the design of thermal insulation.
4.2 Requirements for reactor safety
Design of thermal insulation shall be satisfied with safety requirements about thermal insulation
specified in regulations, codes and standards of locality in which the product is to be manufactured
and used. Thermal insulation shall be carefully selected and methods for their application shall be
specified to ensure the fulfilment of their safety functions and to minimize interference with other
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safety functions in the event of deterioration of thermal insulation. Meanwhile, the safety requirements
of the RCS component shall also be considered and specified in data sheets for thermal insulation.
As an output of thermal insulation design and an input for safety facilities, the debris source caused by
thermal insulation shall not influence the normal operation of emergency core cooling system (ECCS),
pit strainer and other safety facilities. Both the quantity and granulometry of debris shall be considered.
This requirement is for the whole thermal insulation system but not for a single part.
For thermal insulation parts where workers may contact or be close to, the temperature of thermal
insulation outer surface shall be limited to protect the physical security of the workers.
For thermal insulation belonging to nuclear safety related class or category or performing reactor safety
related function, the following safety related requirements can be selectively conducted in the design
of thermal insulation to meet the functional requirements of NPP safety system. For thermal insulation
belonging to non-nuclear safety class or category, the following requirements are not mandatory.
— During normal operation and anticipated incidents, corresponding loads shall be carried, all
function of thermal insulation shall be normally performed for the whole design lifetime.
— During seismic conditions, impact of seismic loads on the insulated and adjacent components shall
be minimized.
— If any safety function needs to be performed by thermal insulation itself, the function reliability
shall be ensured.
4.3 Material selection
4.3.1 General requirements
Materials applied for thermal insulation shall meet the safety requirements of material applied in
NPP reactor according to the regulations and codes pertaining to the locality in which the product
is to be manufactured and used. Debris source caused by material itself shall be satisfied with
requirements in 4.1.
Materials applied in thermal insulation mainly include main insulating material, outer cladding/sealing
material, support/fixation material, etc. Material performance degradation due to the totally received
radiation dose during whole design lifetime shall be considered in the material selection. The maximum
service temperature of all materials shall be higher than the design or operation temperature of
equipment and piping insulated and be with appropriate margin.
4.3.2 Main insulating material
The safety requirement, thermal behaviour, mechanical properties and structure of thermal insulation
would be directly influenced by the main insulating material. Hence, selection of main insulating material
shall be determined firstly. The main insulating material can be classified as the following two types:
— metallic insulating material
— non-metallic insulating material
Based on the two kinds of main insulating material, types of thermal insulation are also classified as
metallic thermal insulation and non-metallic thermal insulation.
For metallic insulating material, the thermal insulated function is achieved by radiative heat transfer
inhibit effect due to the low surface emissivity of material. Hence, surface bright treatable metallic
material with low surface emissivity shall be selected. For instance, austenitic stainless steel, aluminum
or galvanized steel can all be recommended.
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Chemical composition and physical properties (including mechanical property and corrosion resistant
property, etc.) of metallic insulating material shall meet requirements specified in relevant codes and
standards, and be with good processing performance.
For non-metallic insulating material, the thermal insulated function is achieved by convective
heat transfer inhibit effect due to the interior porous structure of material, such as fibre material,
microporous material, etc.
Non-metallic insulating material and their products shall have good resistance to radiation. During
the lifetime, phenomenon including obvious embrittlement, pulverization, contraction and obviously
increased thermal conductivity shall be avoided. The radiation resistance performance of non-metallic
insulating material and their product shall be verified by irradiation test.
Non-metallic insulating material shall be resisted to steam, moisture, fungi, disintegration and fire
during whole design lifetime and under its operation condition.
Any noxious or harmful effect (formaldehyde emission, carcinogenicity and other possible harmful
factors) of non-metallic material shall be limited as far as practicable and respect the the regulations,
codes and standards of locality in which the product is to be manufactured and used. The content of
organic binder shall be controlled.
For non-metallic insulating material directly contacted with equipment and piping insulated, the
influence of stress corrosion cracking tendency on equipment and piping shall be evaluated and the
result shall be available before lot production. For non-metallic insulating material directly contacted
with austenitic steel components, the leachable chloride, fluoride, sodium and silicate ions as well as pH
value of leached water shall be limited.
4.3.3 Outer cladding/sealing material
The outer cladding/sealing material is used for the cladding shell, sealing panel or other outer protective
parts for the main insulating material. During the whole design lifetime, mechanical properties of
material shall be enough to sustain loads acting on the cladding or sealing parts. In order to satisfy
sealing requirement under different operation conditions, processes including riveting, fillet welding,
intermittent welding, seal welding can be selected to assemble the cladding shell or sealing panel. If
the outer cladding/sealing material was different from the main insulating material or the adjacent
contacted equipment or piping material, the influence of corrosion or other negative tendency caused
by the contact between different types of materials shall be evaluated and the result shall be available
before lot production.
4.3.4 Support/fixation material
The support/fixation material is used for support frame, support leg, strap or other supporting and
fixation parts of thermal insulation. During the whole design lifetime, mechanical properties of
material shall be enough to sustain loads acting on the support or fixation parts. If the support/fixation
material was different from the main insulating material or the adjacent contacted equipment or piping
material, the influence of corrosion or other negative tendency caused by the contact between different
types of materials shall be evaluated and the result shall be available before lot production.
4.4 Thermal behaviourr design and test
4.4.1 Thermal behaviourr design
For thermal behaviour design, the surface temperature or heat productivity value of equipment and
piping insulated shall be taken as design input, the heat loss limit of equipment and piping insulated
shall be taken as design target. This heat loss limit could be specified by equipment specification or
other corresponding documents and mainly described by the following parameters:
— heat flux of thermal insulation outer surface
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— temperature of thermal insulation outer surface
— heat loss of thermal insulation
After the above design input and target has been offered or specified, the design thickness of thermal
insulation shall be determined by theoretical calculation method. Calculation of the design thickness is
based on Equation (1) or Equation (2). Equation (1) is suitable for the calculation under flat wall heat
transfer process, Equation (2) is suitable for the calculation under cylinder wall heat transfer process.
Besides, Equation (3) can be used to obtain heat flux from heat loss, then the heat flux can be used for
the calculation of design thickness. Equation (3) also can be used to verify the heat flux calculation
result by comparing with heat loss limit.
The thermal conductivity λ in Equation (1) and Equation (2) can be obtained by querying standards
or performing heat transmission test described in Clause 4.3.2. The heat transfer coefficient h
should consider both of thermal insulation outer surface heat convection transfer coefficient h and
c
heat radiation coefficient h , which is shown in Equation (4). For safety, appropriate margin shall be
r
considered for the design thickness.
It shall be noted that the calculated design thickness is the net thickness of main insulating material,
not including outer cladding, sealing or any other material without thermal insulate function.
δ 1
 
qT=Δ / + (1)
 
λ h
 
 dd 
1
00
qT=Δ /l×+n (2)
 
2λ dh
 
i
Qq=×A (3)
hh=+h (4)
cr
where
q is heat flux of thermal insulation
ΔT is temperature difference between inner and outer surface of thermal insulation
λ is thermal conductivity of thermal insulation
δ is design thickness of thermal insulation under flat wall heat transfer process
d is design outer diameter of thermal insulation under cylinder wall heat transfer process
0
d is design inner diameter of thermal insulation under cylinder wall heat transfer process
i
h is surface coefficient of heat transfer of thermal insulation
h is surface coefficient of heat convection transfer of thermal insulation
c
h is surface coefficient of heat radiation transfer thermal insulation
r
Q is heat loss of thermal insulation
A is thermal transfer area of thermal insulation
In the calculation of the outer surface heat convection transfer coefficient, the shape and direction of
thermal insulation, the ambient temperature and the ventilation condition should all be considered.
According to the different conditions, different calculation method should be selected for heat
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convection transfer coefficient. Heat radiation coefficient should be in accordance with the property of
main insulating material itself.
Besides, influence of displacement caused by the thermal expansion of thermal insulation itself and
equipment and piping insulated should be considered, expansion and contraction during start-up and
shutdown of the reactor should also be considered. Typical insulation parts, of which the function is
obviously influenced by thermal stress or deformation, shall be verified by corresponding analysis.
Solutions based on formula calculation are acceptable if the object geometry and thermal transfer
conditions are simple enough. For calculation procedure considering various thermal transfer influence
factors or calculation object with complex and irregular geometries, finite element or other proven
equivalent analysis methods is recommended to calculate the heat flux, temperature distribution and
heat loss.
If the heat exchange paths between inner and outer side of thermal insulation cannot be totally avoided,
the influence of chimney effect shall be considered in thermal behaviour calculation.
4.4.2 Thermal behaviourr test
After the main insulating material has been selected, the thermal conductivity is recommended to be
obtained by heat transmission test. This heat transmission test can be performed for material itself or
typical thermal insulation panel. In order to obtain thermal conductivity with more approaching to real
production, the unidirectional heat transmission test for typical thermal insulation panel is preferred.
For supplier who performs thermal insulation design for first time, or new geometry, new material, new
process applied in the design and manufacturing of thermal insulation without previous experience
of lot production, a heat transmission simulation test can be selectively performed before thermal
insulation product is finally
...