ISO 4233:2023

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: Published
• Publication Date: 05-Mar-2023
• 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: 6060 - International Standard published
• Start Date: 06-Mar-2023
• Due Date: 13-Jan-2024
• Completion Date: 06-Mar-2023

Relations

• Consolidated By: ISO 14723:2025 - Oil and gas industries including lower carbon energy - Pipeline transportation systems - Subsea pipeline valves
• Effective Date: 13-Apr-2024

Overview

ISO 4233:2023 - "Reactor technology - Nuclear fusion reactors - Hot helium leak testing method for high temperature pressure-bearing components in nuclear fusion reactors" - specifies a standardized method for assessing leak tightness of metallic pressure-bearing components at elevated temperature using hot helium leak testing. The method measures total leakage rates in a vacuum chamber by detecting tracer gas (helium or helium mixtures) that escapes from a pressurized component during thermal and pressure cycles at its operating conditions. The standard is designed for in‑vessel components in nuclear fusion reactors (ultra‑high vacuum environments down to 10‑6 Pa) but also applies to other evacuated and pressurized metallic equipment such as tanks, pipes and valves in power, aerospace and other nuclear applications.

Key topics and technical requirements

• Test principle: Evacuate the test chamber, pressurize the component with helium tracer gas, and collect leaked helium via a vacuum pumping system and a tracer gas leak detector (helium leak detector or mass spectrometer).
• Sensitivity: Minimum detectable leakage rate can be as low as 1×10‑10 Pa·m3/s depending on component geometry, materials, and test-system performance.
• Calibration and validation:
  • Use an authorised reference leak for facility calibration.
  • Systematic error (D) must be validated and kept within ±20%.
  • Determine the facility’s minimum detectable leakage rate and detector response/cleanup times.
• Apparatus and setup: Requirements for vacuum chamber, pumping, heating and temperature control, temperature uniformity, reference leaks and tracer gas detectors are specified.
• Test procedures:
  • Component preparation (including vacuum baking where required).
  • Initial cold leak test, hot leak testing at operating temperature(s), cyclic temperature and pressure testing, and final cold test.
  • Record heating/cooling rates and leakage rates at each test temperature and pressure.
• Personnel and reporting: Personnel competence is addressed via normative references; detailed test-report content is required.

Practical applications and users

• Use ISO 4233 for validating leak tightness of high‑temperature, pressure‑bearing components that operate in ultra‑high vacuum and pressurized coolant environments - primarily fusion reactor in‑vessel components.
• Also applicable to leak testing of welds and pressure-retaining metallic assemblies in power plants, aerospace systems, and other nuclear reactors.
• Typical users: test engineers, NDT (non‑destructive testing) teams, QA/QC engineers, design and commissioning teams, and regulator/compliance bodies responsible for reactor and pressure system integrity.

Related standards

• ISO 20485:2017 - Non‑destructive testing - Leak testing - Tracer gas method
• ISO 20484 - Leak testing - Vocabulary
• ISO 9712 - Qualification and certification of NDT personnel
• EN 1779:1999 - Leak testing - Criteria for method and technique selection

Keywords: ISO 4233, hot helium leak testing, nuclear fusion reactors, high temperature pressure‑bearing components, leak tightness, vacuum chamber, tracer gas, helium leak detector, minimum detectable leakage rate.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 4233
First edition
2023-03
Reactor technology — Nuclear
fusion reactors — Hot helium leak
testing method for high temperature
pressure-bearing components in
nuclear fusion 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
Reference number
© ISO 2023
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
Contents Page
Foreword .iv
Introduction .v
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 . 7
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 . 8
7.8 Other equipment . 8
8 Test component preparation .8
8.1 Preliminary tests before hot helium leak test . 8
8.2 Vacuum baking . 9
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 .11
10.1 Installation of the component into the test system . 11
10.2 Initial set-up of the leak testing system . 11
10.3 Initial helium leak testing . 11
10.4 Helium leak testing at elevated temperature . 11
10.5 Cyclic hot helium leak testing . 12
10.6 Final cold helium leak testing . 12
11 Test report .12
iii
Foreword
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This document was prepared by Technical Committee ISO/TC 85, Nuclear technology, nuclear
technologies, and radiological protection, Subcommittee SC 6, Reactor technology.
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iv
Introduction
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.
v
INTERNATIONAL STANDARD ISO 4233:2023(E)
Reactor technology — Nuclear fusion reactors — Hot
helium leak testing method for high temperature pressure-
bearing components in nuclear fusion reactors
1 Scope
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
-10 3
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-
-6
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 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 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 20485:2017, 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.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
background noise
I
n
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.
4 Symbols
The symbols and units given in Table 1 apply to this document.
Table 1 — Symbols and units
Symbol Description Unit
The volume fraction of the helium gas when a helium gas mixture is used for the
C %
leak test
D Systematic error of the leakage rate measurement %
I Background noise Pa·m /s
n
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
The minimum detectable leakage rate of the test facility, named as the minimum
Q Pa·m /s
s
detectable leakage rate of the system
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
CL
coefficient at the conditions to calibrate the leak test system
Actual total leakage rate of the component referred to its working pressure and
q Pa·m /s
G
temperature in operation
Stable background signal in leakage rate measurement, reading from a tracer gas
R Pa·m /s
CL
leak detector before opening a reference leak for calibration of a leak test system
Stable background signal in leakage rate measurement, reading from the tracer gas
R Pa·m /s
L
leak detector after closing the reference leak
Stable leak signal in leakage rate, reading from the tracer gas leak detector after
S Pa·m /s
CL
opening the reference leak for calibration of the leak test system
Stable leak signal in leakage rate measurement, reading from the tracer gas leak de-
S Pa·m /s
L
tector during high-pressure helium gas applied to the component in the leak test
T The elevated test temperature °C
test
The temperature of the reference leak in its calibration, certified by an authorized
T °C
metrological verification agency
The ambient temperature of the reference leak in the calibration of the leak test
T °C
system
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
5 Principles and techniques of detection
5.1 The vacuum box technique for closed objects B.2.1 in ISO 20485:2017 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.
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)
q
CL
where q is determined by Formula (2):
CL
qT=⋅ Q 1 +−(%T ⋅α ] (2)
[ )
CL 0 10
5.3 The minimum detectable leakage rate, Q , of the leak test system shall be checked according to
s
the calibration results. It shall be lower than the actual total leakage, q , of the test component, which
G
shall be calculated by Formula (4) in 5.3.2.
5.3.1 Q is calculated by Formula (3):
s
I
n
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, p , in
G 0
its operation, Formulae (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
G
Formula (4):
()SR− 1
L L
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):
G
()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 applies for the selection of the test conditions, which shall be consistent with the
operating conditions of the component, including temperature and pressure. The temperature of
the component under test should not be lower than the maximum temperature of its inner surface
contacting with the working medium or coolant under operation. Otherwise, a temperature correction
shall be made to the total leakage rate of the component in accordance with EN 1779:1999, 7.3.2. In
addition, the component should go through the operating temperature at least once while the
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