IEC 61468-2021 pdf free.Nuclear power plants – Instrumentation systems important to safety – In-core instrumentation: Characteristics and test methods of self-powered neutron detectors.
This document applies to in-core neutron detectors, viz, self-powered neutron detectors (SPNDs), which are intended for application in systems important for nuclear reactor safety:
protection, instrumentation and control. This document contains SPND characteristics and test methods, In this document, the main sources of errors, and the possibilities for their minimization are also considered
Self-powered neutron detectors can be used for measurement of neutron fluence rate and associated parameters in nuclear reactors. Most popular for the indicated applications are detectors with rhodium emitters.
In this document dynamic characteristics, emitter burn-up, identity and other factors influencing operational characteristics of detectors are considered,
Besides SPNDs with rhodium emitters, SPNDs with emitters from other materials and their main characteristics are also considered in this document.
This document contains requirements, recommendations and instructions concerning selection of SPND type and characteristics for various possible applications. This document about SPNDs uses the basic requirements of IEC 61513 and IEC 60568 and complements them with more specific provisions in compliance with IAEA Safety Guides.
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.
IEC 60515:2007, Nuclear power plants — Instrumentation important to safety — Radiation detectors — Characteristics and test methods
IEC 60568:2006, Nuclear power plants — Instrumentation important to safety — In-core instrumentation for neutron uluence rate (flux) measurements in power reactors
IEC/IEEE 60780-323:2016, Nuclear facilities — Electrical equipment important to safety — Qualification
IEC 61226, Nuclear power plants — Instrumentation, control and electrical power systems important to safety — Categorisation of functions and classification of systems
IEC 61513, Nuclear power plants — Instrumentation and control important to safety — General requirements for systems
5 Self-powered neutron detectors general advantages and disadvantages
In self-powered neutron detectors (SPNDs), the interactions of neutrons and atomic nuclei are used to produce a current which is proportional to the neutron fluence rate. The principles and characteristics of SPND design and operation are given in Annex A.
When compared to other types of detectors, they have the following advantages:
— no need of power supply;
— simple and robust construction;
— relatively small mechanical “size” well-suited for in-core installation;
— good stability under temperature, pressure, radiation and other conditions.
The main disadvantages of SPNDs are the low signal level and the inertia of the neutron component of the signal.
6 Composition and construction
A typical SPND consists of an emitter, made of a material with a large neutron interaction cross-section, its surrounding insulator, collector and lead cable.
SPNDs are divided into two types according to their design and manufacturing technology:
— integral (or cable-type) SPND (see Figure 1), in which the signal wire of the lead cable mates directly to the emitter; isolation around the emitter is identical to the isolation of the signal line, and the collector is an extension of the signal line sheath;
— modular (or prefabricated) SPND (see Figure 2), which is made from separate detector and lead cable sections.IEC 61468 pdf free download.