ISO/FDIS 23466

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
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ISO/DIS 23466:2019(E)
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ISO/DIS 23466:2019(E)
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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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This document was prepared by Technical Committee ISO/TC 85, Nuclear energy, nuclear technologies,

Any feedback or questions on this document should be directed to the user’s national standards body. A

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

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:

This document specifies the basic requirements related to the design of thermal insulation of reactor

This document mainly applies to pressure water reactor (PWR) nuclear power plants. For other reactor

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 —

ISO 8497, Thermal insulation — Determination of steady-state thermal transmission properties of thermal

ISO 8990, Thermal insulation — Determination of steady-state thermal transmission properties —

For the purposes of this document, the terms and definitions given in ISO 7345, ISO 9229 and the

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

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

Note 2 to entry: The detailed description of typical geometry of metallic thermal insulation is shown in Annex A.

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

— 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.

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

path with high heat flow, caused by geometry with high thermal conductivity material connecting the

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

— Mechanical properties design and test, including seismic resistance, vibration resistance, etc.

Besides, other requirements including installation, remove, maintenance, in-service inspection and

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

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

— If any safety function needs to be performed by thermal insulation itself, the function reliability

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

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

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:

Based on the two kinds of main insulating material, types of thermal insulation are also classified as

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

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

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,

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

Non-metallic insulating material shall be resisted to steam, moisture, fungi, disintegration and fire

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

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

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

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.

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

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

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

heat radiation coefficient h , which is shown in Equation (4). For safety, appropriate margin shall be

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.

ΔT is temperature difference between inner and outer surface 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

d is design inner diameter of thermal insulation under cylinder wall heat transfer process

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

convection transfer coefficient. Heat radiation coefficient should be in accordance with the property of

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

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.

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