IEC 61468:2021 pdf download

IEC 61468:2021 pdf download.Nuclear power plants – Instrumentation systems important to safety – In-core instrumentation: Characteristics and test methods of self-powered neutron detectors
1 Scope
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.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.3.1 background-compensation <of a self-powered neutron detector signal> method employed for compensation of background contribution to the self-powered neutron detector current Note 1 to entry: This is usually accomplished by placing an “emitterless” background detector in the in-core assembly, or by using detectors with an internal compensating lead wire. Note 2 to entry: An equivalent term is “lead-compensation”. 3.2 beta decay radioactive decay process in which mass number A remains unchanged, but the atomic number Z changes Note 1 to entry: Processes include electron emission (b– decay), electron capture, and positron emission (b+ decay). 3.3 burn-up depletion or reduction of target atoms when exposed to a thermal neutron flux density over time, due to conversion to other radioisotopes 3.4 burn-up life time after which, at a given value of the neutron fluence rate of given energy distribution, the amount of emitter sensitive material will decrease to such an extent that the characteristics of the detector go beyond the tolerance established for their given application 3.5 Compton effect effect which occurs when an incident high-energy photon is deflected from its original path by an interaction with an electron Note 1 to entry: The electron is ejected from its orbital position and the x-ray photon loses energy because of the interaction but continues to travel through the material along an altered path. Energy and momentum are conserved in this process. The energy shift depends on the angle of scattering and not on the nature of the scattering medium. Since the scattered photon has less energy, it has a longer wavelength than the incident photon. Note 2 to entry: An equivalent term is “Compton scattering”. [SOURCE: IEC 60050-395:2014, 395-02-07] 3.6 cross-section σ measure of the probability of a nuclear reaction of a specific type, stated as the effective area which targets particles present to incident particles for that process 3.9 in-core neutron detector detector, fixed or movable, designed for the measurement of neutron fluence rate at a defined region of a reactor core 3.10 integral self-powered neutron detector self-powered neutron detector in which the lead cable section is an extension of the detector section, i.e. the emitter is directly attached to the core/signal wire; both sections share common insulation, and the collector of the detector section is also the outer sheath of the lead cable section (see Figure 1) Note 1 to entry: An equivalent term is “cable-type self-powered neutron detector”. 3.11 modular self-powered neutron detector self-powered neutron detector made by mechanically joining, welding or brazing a detector (emitter, insulator, collector) to a lead cable (core/signal wire, insulator, outer sheath) (see Figure 2) Note 1 to entry: An equivalent term is “prefabricated self-powered neutron detector”. 3.12 isotope variants of a chemical element that differ by atomic mass, having the same number of protons and differing in the number of neutrons in the nucleus