IEC 61468 pdf – 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 andtest methods. ln this document, the main sources of errors,and the possibilities for theirminimization are also considered.
Self-powered neutron detectors can be used for measurement of neutron fluence rate andassociated parameters in nuclear reactors. Most popular for the indicated applications aredetectors with rhodium emitters.
In this document dynamic characteristics, emitter burn-up,identity and other factorsinfluencing operational characteristics of detectors are considered.
Besides SPNDs with rhodium emitters，SPNDs with emitters from other materials and theirmain characteristics are also considered in this document.
This document contains requirements, recommendations and instructions concerningselection of SPND type and characteristics for various possible applications. This documentabout SPNDs uses the basic requirements of IEC 61513 and lEC 60568 and complementsthem with more specific provisions in compliance with IAEA Safety Guides.
The following documents are referred to in the text in such a way that some or all of theircontent constitutes requirements of this document. For dated references，only the editioncited applies. For undated references, the latest edition of the referenced document (inciuding
any amendments) applies.
IEC 60515:2007,Nuclear power plants – Instrumentation important to safety – Radiationdetectors – Characteristics and test methods
IEC 60568;2006, Nuclear power plants – Instrumentation important to safety – In-coreinstrumentation for neutron fluence rate (flux) measurements in power reactors
IEC/IEEE60780-323:2016,Nuclear facilities – Electricalequipment importantto safety -Qualification
IEC 61226，Nuclear power plants – Instrumentation, control and electrical power systemsimportant to safety – Categorisation of functions and classification of systems
IEC 61513，Nuclear power plants – Instrumentation and control important to safety – Generalrequirements for systems
3Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the followingaddresses:
-lEC Electropedia: available at http://www.electropedia.orgl
. Iso Online browsing platform: available at http://www.iso.orglobp
method employed for compensation of background contribution to the self-powered neutrondetector current
Note 1 to entry.: This is usually accomplished by placing an “emitterless background detector in the in-coreassembly，or by using detectorswith an internal compensating lead wire.
Note 2 to entry: An equivalent term is “lead-compensation”.
radioactive decay process in which mass number A remains unchanged， but the atomicnumber Z changes
Note 1 to entry: Processes include electron emission (b- decay),electron capture,and positron emission (b+decay).
depletion or reduction of target atoms when exposed to a thermal neutron flux density overtime, due to conversion to other radioisotopes
time after which, at a given value of the neutron fluence rate of given energy distribution, theamount of emitter sensitive material will decrease to such an extent that the characteristics ofthe detector go beyond the tolerance established for their given application
effect which occurs when an incident high-energy photon is deflected from its original path byan 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 theinteraction but continues to travel through the materialalong an altered path. Energy and momentum areconserved in this process. The energy shit depends on the angle of scattering and not on the nature of thescattering medium. Since the scattered photon has less energy,it has a longer wavelength than the incidentphoton.
Note 2 to entry: An equivalentterm is “Compton scattering”.[SOURCE: IEC 60050-395:2014,395-02-07]
measure of the probability of a nuclear reaction of a specific type, stated as the effective area