IEC 61468:2021

IEC 61468 ®
Edition 2.0 2021-04
INTERNATIONAL
STANDARD
Nuclear power plants – Instrumentation systems important to safety –
In-core instrumentation: Characteristics and test methods of self-powered
neutron detectors
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IEC 61468 ®
Edition 2.0 2021-04
INTERNATIONAL
STANDARD
Nuclear power plants – Instrumentation systems important to safety –

In-core instrumentation: Characteristics and test methods of self-powered

neutron detectors
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.120.20 ISBN 978-2-8322-9706-3

– 2 – IEC 61468:2021 © IEC 2021
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 8
2 Normative references . 8
3 Terms and definitions . 8
4 Abbreviated terms . 12
5 Self-powered neutron detectors general advantages and disadvantages . 13
6 Composition and construction . 13
7 Application recommendations . 16
7.1 General . 16
7.2 Fluence rate mapping – Core monitoring and surveillance . 16
7.3 Power regulation – Feedback control . 16
7.4 Core protection . 16
7.5 Reactor noise analysis . 16
7.6 Classification . 16
8 Design recommendations . 17
8.1 General . 17
8.2 Reproducibility of SPND characteristics . 17
8.3 Background signal . 17
8.4 Electrical interference noise . 17
8.5 Lifetime . 17
9 Test methods . 17
9.1 General . 17
9.2 Prototype testing . 18
9.3 Production tests . 18
10 Detector calibration . 18
10.1 Place of calibration . 18
10.2 Absolute calibration . 19
10.3 Comparison calibration . 19
10.4 In-core calibration . 19
10.5 Calibration procedure . 19
10.6 Recommended calibration periods . 20
Annex A (informative)  Self-powered detector principles and characteristics . 21
A.1 SPND response mechanisms . 21
A.2 Beta decay (delayed response) . 21
A.3 Neutron capture (prompt response) . 21
A.4 Photoelectric effect (prompt response) . 21
A.5 Compton effect (prompt response) . 21
A.6 Nature of SPND response . 22
A.7 Thermal neutron interactions. 22
A.8 Gamma interactions . 22
A.9 Dynamic characteristics of SPND . 22
A.10 Detector burn-up life . 23
A.11 Measurement errors . 23
A.11.1 General . 23
A.11.2 Error for determination of SPND actual response . 23

A.11.3 Error determined by gamma-component of SPND current . 24
A.11.4 Error determined by leakage currents . 24
A.11.5 Error determined by signal wire current . 25
A.12 Self-powered detector operating characteristics . 25
A.12.1 General . 25
A.12.2 Vanadium emitter characteristics . 26
A.12.3 Cobalt emitter characteristics . 26
A.12.4 Rhodium emitter characteristics . 26
A.12.5 Silver emitter characteristics . 27
A.12.6 Platinum emitter characteristics . 27
A.12.7 Hafnia emitter characteristics . 27
A.13 Self-powered detector assemblies. 28
A.13.1 General . 28
A.13.2 Typical bottom-mounted rhodium self-powered detector assembly for
pressurized light water reactors . 28
A.13.3 Typical top-mounted rhodium self-powered detector assembly for
VVER–type light water reactors . 28
A.13.4 Typical top-mounted cobalt self-powered detector assembly for
pressurized light water reactors . 28
A.13.5 Typical heavy water reactor self-powered detector assembly . 29
Bibliography . 34

Figure 1 – Typical integral self-powered neutron detector . 13
Figure 2 – Typical modular self-powered neutron detector . 13
Figure 3 – Typical background detector . 15
Figure 4 – Typical SPND with built-in background detector . 16
Figure A.1 – Simplified equivalent circuit of the SPND . 25
Figure A.2 – Bottom-mounted rhodium self-powered detector assembly for pressurized
water reactors . 29
Figure A.3 – Top-mounted rhodium self-powered detector assembly for VVER reactors
with four thermocouples . 30
Figure A.4 – Top-mounted rhodium self-powered detector assembly for VVER reactors
with level sensor . 31
Figure A.5 – Top-mounted cobalt self-powered detector assembly for pressurized
water . 32
Figure A.6 – CANDU pressurized heavy water reactor self-powered detector assembly . 33

Table 1 – Characteristics of SPND emitters . 14
Table A.1 – Examples of specifications for typical SPNDs used in power reactors . 26

– 4 – IEC 61468:2021 © IEC 2021
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
NUCLEAR POWER PLANTS – INSTRUMENTATION SYSTEMS IMPORTANT
TO SAFETY – IN-CORE INSTRUMENTATION: CHARACTERISTICS AND
TEST METHODS OF SELF-POWERED NEUTRON DETECTORS

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