ISO 23466:2020

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
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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
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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
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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.
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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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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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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
...