ISO 4233

Reactor technology — Nuclear fusion reactors — Hot helium leak testing method for high temperature pressure-bearing components in nuclear fusion reactors

This document specifies the methods and techniques for leak tightness assessment of a metallic component at high temperature by measuring its total leakage rates in a vacuum chamber with a tracer gas leak detector and high-pressure helium gas or the gas mixture flowing out of the component as tracer gas during its thermal and pressure cycles at its operating conditions. The minimum detectable leakage rate can be as low as 10-10 Pa·m3/s, depending on the dimension, external configuration complexity and materials of the component, and is strongly related to the test system and the test conditions. This document is applicable for the hot helium leak test of in-vessel components as per its normal operating conditions in nuclear fusion reactors, which operate at elevated temperatures in an ultra-high vacuum environment down to 10-6 Pa and with inner flowing-coolant at operating pressure. It is also applicable to the overall leak tightness test of welds in other metallic components and equipment that could be evacuated and pressurized, such as pressurized tanks, pipes and valves in power plants, aerospace and other nuclear reactors.

Technologie du réacteur — Réacteurs à fusion nucléaire — Méthode de contrôle d’étanchéité par détection de fuite d’hélium à chaud pour les composants sous pression à haute température de réacteurs à fusion nucléaire

General Information

• Status: Not Published
• 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 2 - Research, test and isotope-production reactors
• Current Stage: 6000 - International Standard under publication
• Completion Date: 15-Feb-2023

Standards Content (Sample)

DRAFT INTERNATIONAL STANDARD
ISO/DIS 4233
ISO/TC 85/SC 6 Secretariat: DIN
Voting begins on: Voting terminates on:
2022-07-01 2022-09-23
Hot helium leak testing method for high temperature
pressure-bearing components in nuclear fusion reactors
ICS: 27.120.20
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
This document is circulated as received from the committee secretariat.
NOT BE REFERRED TO AS AN INTERNATIONAL
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Reference number
NATIONAL REGULATIONS.
ISO/DIS 4233:2022(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
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PROVIDE SUPPORTING DOCUMENTATION. © ISO 2022
---------------------- Page: 1 ----------------------
ISO/DIS 4233:2022(E)
DRAFT INTERNATIONAL STANDARD
ISO/DIS 4233
ISO/TC 85/SC 6 Secretariat: DIN
Voting begins on: Voting terminates on:
Hot helium leak testing method for high temperature
pressure-bearing components in nuclear fusion reactors
ICS: 27.120.20
COPYRIGHT PROTECTED DOCUMENT
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENT AND APPROVAL. IT IS
© ISO 2022
THEREFORE SUBJECT TO CHANGE AND MAY
This document is circulated as received from the committee secretariat.

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

NOT BE REFERRED TO AS AN INTERNATIONAL

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on STANDARD UNTIL PUBLISHED AS SUCH.

the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below

IN ADDITION TO THEIR EVALUATION AS

or ISO’s member body in the country of the requester. BEING ACCEPTABLE FOR INDUSTRIAL,

TECHNOLOGICAL, COMMERCIAL AND
ISO copyright office
USER PURPOSES, DRAFT INTERNATIONAL
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STANDARDS MAY ON OCCASION HAVE TO
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CH-1214 Vernier, Geneva
POTENTIAL TO BECOME STANDARDS TO
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WHICH REFERENCE MAY BE MADE IN
Reference number
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NATIONAL REGULATIONS.
Website: www.iso.org ISO/DIS 4233:2022(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
Published in Switzerland
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
© ISO 2022 – All rights reserved
PROVIDE SUPPORTING DOCUMENTATION. © ISO 2022
---------------------- Page: 2 ----------------------
ISO/DIS 4233:2022(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ..................................................................................................................................................................................... 1

3 Terms and definitions .................................................................................................................................................................................... 1

4 Symbols .......................................................................................................................................................................................................................... 2

5 Principles and techniques of detection ....................................................................................................................................... 2

6 Personnel ..................................................................................................................................................................................................................... 5

7 Apparatus .................................................................................................................................................................................................................... 5

7.1 General ........................................................................................................................................................................................................... 5

7.2 Test component and vacuum chamber .............................................................................................................................. 6

7.3 The vacuum pumping system ................................................................................................................................................... 7

7.4 Heating and temperature control system ...................................................................................................................... 7

7.5 Temperature uniformity requirement .............................................................................................................................. 7

7.6 Reference leak ......................................................................................................................................................................................... 7

7.7 Tracer gas leak detector ................................................................................................................................................................. 7

7.8 Other equipment ................................................................................................................................................................................... 8

8 Test component preparation ..................................................................................................................................................................8

8.1 Preliminary tests before hot helium leak test ............................................................................................................ 8

8.2 Vacuum baking ....................................................................................................................................................................................... 8

9 Calibration ..................................................................................................................................................................................................................9

9.1 General ........................................................................................................................................................................................................... 9

9.2 Response and cleanup time measurements ................................................................................................................. 9

9.3 Leak detector validation and determination of minimum detectable leakage rate ................. 9

10 Testing procedures ...........................................................................................................................................................................................9

10.1 Installation of the component into the test system ............................................................................................... 9

10.2 Initial set-up of the leak testing system ........................................................................................................................ 10

10.3 Initial helium leak testing .......................................................................................................................................................... 10

10.4 Helium leak testing at elevated temperature ........................................................................................................... 10

10.5 Cyclic hot helium leak testing ................................................................................................................................................. 10

10.6 Final cold helium leak testing ................................................................................................................................................ 10

11 Test report ...............................................................................................................................................................................................................11

iii
© ISO 2022 – All rights reserved
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ISO/DIS 4233:2022(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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Barriers to Trade (TBT) see the following URL: Foreword - Supplementary information

The committee responsible for this document is ISO/TC 85, Nuclear technology, nuclear technologies, and

radiological protection, Subcommittee SC 6, Reactor technology.
© ISO 2022 – All rights reserved
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DRAFT INTERNATIONAL STANDARD ISO/DIS 4233:2022(E)
Hot helium leak testing method for high temperature
pressure-bearing components in nuclear fusion reactors
1 Scope

Hot helium leak testing can realize more reliable leak tightness assessment than the conventional cold

helium leak testing for components that run at elevated temperatures. It gives the total leakage rate of

a component at its operating temperature and pressure, and could greatly reduce its operational leak

risk.

This document specifies the methods and techniques for leak tightness assessment of a metallic

component at high temperature by measuring its total leakage rates in a vacuum chamber with a tracer

gas leak detector and high-pressure helium gas or the gas mixture flowing out of the component as

tracer gas during its thermal and pressure cycles as these at its operating conditions. The minimum

-10 3

detectable leakage rate can be as low as 10 Pa ⋅ m /s, depending on the dimension, external

configuration complexity and materials of the component, and is strongly related to the test system and

the test conditions.

This document is applicable for the hot helium leak test of in-vessel components as per its normal

operating conditions in nuclear fusion reactors, which operate at elevated temperatures in an ultra-

high vacuum environment down to 10 Pa and with inner flowing-coolant at operating pressure. It is

also applicable to the overall leak tightness test of welds in other metallic components and equipment

that could be evacuated and pressurized, such as pressurized tanks, pipes and valves in power plants,

aerospace and other nuclear reactors.
2 Normative references

The following documents, in whole or in part, are normatively referenced in this document and are

indispensable for its application. For dated references, only the edition cited applies. For undated

references, the latest edition of the referenced document (including any amendments) applies.

ISO 9712, Non-destructive testing — Qualification and certification of NDT personnel

ISO 20484, Non-destructive testing — Leak testing — Vocabulary
ISO 20485, Non-destructive testing — Leak testing — Tracer gas method

EN 1779:1999, Non-destructive testing-Leak testing -Criteria for method and technique selection

3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 20484 and the following

apply.
3.1
background noise
maximum vibration value of the background signal in a specified period
Note 1 to entry: The specified period is usually 5 min.

Note 2 to entry: The large pulse signal appearing occasionally during the test process should be ignored.

© ISO 2022 – All rights reserved
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ISO/DIS 4233:2022(E)
4 Symbols
The symbols and units in Table 1 apply to this document.
Table 1 — Symbols and units
Symbol Description Unit
P The maximum working pressure of a component in operation MPa
P Actual helium pressure applied to the component in a helium leak test MPa
test
I Background noise Pa ⋅ m /s
Stable background signal in leakage rate measurement, reading from a tracer gas
R Pa ⋅ m /s

leak detector before opening a reference leak for calibration of a leak test system

Stable leak signal in leakage rate, reading from the tracer gas leak detector after

S Pa ⋅ m /s
opening the reference leak for calibration of the leak test system

Stable background signal in leakage rate measurement, reading from the tracer gas

R Pa ⋅ m /s
leak detector after closing the reference leak
Stable leak signal in leakage rate measurement, reading from the tracer gas leak
S Pa ⋅ m /s

detector during high-pressure helium gas applied to the component in the leak test

The standard leakage rate of the reference leak at its calibration conditions, certi-

Q Pa ⋅ m /s
fied by an authorized metrological verification agency
The standard leakage rate of the reference leak corrected by a temperature
q Pa ⋅ m /s
coefficient at the conditions to calibrate the leak test system
The minimum detectable leakage rate of the test facility, named as the minimum
Q Pa ⋅ m /s
detectable leakage rate of the system
Actual total leakage rate of the component referred to its working pressure and
q Pa ⋅ m /s
temperature in operation

The temperature coefficient for correcting a reference leak, in the range of 2 % to

-1 -1
α K or °C
7 %, certified by an authorized metrological verification agency
D Systematic error of the leakage rate measurement %
The volume fraction of the helium gas when a helium gas mixture is used for the
C %
leak test

The ambient temperature of the reference leak in the calibration of the leak test

T °C
system

The temperature of the reference leak in its calibration, certified by an authorized

T °C
metrological verification agency
T The elevated test temperature °C
test
5 Principles and techniques of detection

5.1 The vacuum box technique for closed objects B.2.1 in ISO 20485 partially applies for this hot

helium leak test. The test component shall be evacuated until the pressure is down to less than 100

Pa, and is then filled with helium tracer gas to its test pressure through a pipe connection to a tracer

gas source. The test pressure should be in the range not higher than its operating pressure when the

pressure gets stable. A pressure difference across its wall is obtained by placing it in a vacuum chamber.

If there are leaks in the test components, the tracer gas or its mixture will flow out of the component

and into the vacuum chamber. All of the leaked and the background tracer gases are collected by a

tracer gas leak detector, either a helium leak detector or a mass spectrometer leak detector (MSLD),

through a vacuum pumping system, and the reading shall be recorded.
© ISO 2022 – All rights reserved
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ISO/DIS 4233:2022(E)

5.2 Prior to any leak test, the test facility shall be calibrated by a reference leak. The systematic error

D, calculated by Formula (1), shall be in the range of ±20 %. This is taken as a criterion for validation of

the test system.
()SR−−q
CL CL CL
D= ×100% (1)
Where q is determined by Formula (2),
qQ=× 1+−TT ×α% (2)
[]()
CL 00

5.3 The minimum detectable leakage rate Q of the leak test system shall be checked according to the

calibration results. It shall be lower than the actual total leakage q of the test component, which shall

be calculated by Formula (4) in 5.3.2.
5.3.1 Q is calculated by Formula (3),
Q = ×q (3)
s CL
()SR−
CL CL

5.3.2 For calculation of the total leakage rate q of the component under the working pressure in its

operation, Formulas (4) and (5) shall be applied as referring to various testing pressure conditions

-5 3

when the leakage rate is not higher than 10 Pa ⋅ m /s. It shall be lower than the allowable maximum

leakage rate of the component in operation for acceptance.

When the tracer gas pressure in the leak test is the same as the specified operating pressure of the

component or between the two is within a tolerance of ±5 %, the total leakage rate q is determined by

Formula (4).
()SR− 1
q = ××q (4)
G CL
()SR− C
CL CL

When the tracer gas pressure is more different from the operating pressure of the component, the total

leakage rate q of the component shall be determined by Formula (5).
()SR− 1 P
LL 0
q = ××q × (5)
G CL
()SR− C P
CL CL test

Where the effect of the downstream pressure (the vacuum pressure) is ignored as it is quite lower than

the upstream pressure (tracer gas pressure P ) in the leak test.
test
5.4 EN 1779:1999 applies for the selectio
...