BS IEC 61468 pdf download – Nuclear power plants — In-core instrumentation — Characteristics and test methods of self-powered neutron detectors
1 scope and object
This International Standard applies to in-core neutron detectors and instrumentation whichare designed for purposes important to safety: protection，control and information. lt isrestricted to characteristics and test methods for self-powered neutron detectors (SPNDs).Self-powered neutron detectors can be used for neutron fluence rate (flux) measurementsand spatial power measurements in nuclear reactors. This standard gives requirements,recommendations and guidance on selection of the type and characteristics of SPNDs fordifferent possible applications of SPNDs.
For the principles of overall plant and l&C system design and the purpose of neutron fluencerate measurements，reference should be made to general principles of nuclear reactorinstrumentation according to lAEA Codes and Safety Guides and lEC 61513.
Normative references
The following normative documents contain provisions which，through reference in this text,constitute provisions of this International Standard. For dated references,subsequentamendments to, or revisions of,any of these publications do not apply.However,parties toagreements based on this International Standard are encouraged to investigate the possibilityof applying the most recent editions of the normative documents indicated below. Forundated references,the latest edition of the normative document referred to applies.Members of lEC and ISo maintain registers of currently valid International Standards.
IEC 60050(394):1995,International Electrotechnical Vocabulary (IEV)Chapter 394: Nuclearlnstrumentation: Instruments
IEC 60515:1975, Radiation detectors for the instrumentation and protection of nuclearreactors; characteristics and test methods
IEC 60568:1977, In-core instrumentation for neutron fluence rate (flux) measurements inpower reactors
IEC 61226:1993, Nuclear power plants – Instrumentation and control systems important forsafety – Classification
IEC 61513，Nuclear power plants – Instrumentation and control for systems important tosafety – General requirements for systems 1)
3Definitions and abbreviations3.1 Definitions
For the purpose of this publication, the following definitions apply:
3.1.1
background or lead-compensation (of a self-powered detector signal)
a method employed to correct the current from a SPND for background contribution. This isusually accomplished by placing an “emitterless” background detector in the in-coreassembly, or by using detectors with an internal compensating lead wire (see figure 3)
3.1.2
beta decay
radioactive decay process in which mass number A remains unchanged but the atomicnumber Z changes. Processes include electron emission (8- decay), electron capture,andpositron emission (B+ decay)
3.1.3
burn-up
depletion or reduction of target atoms when exposed to a thermal neutron fluence rate overtime, due to conversion to other radioisotopes
3.1.4
burn-up life (of a neutron detector)
estimated fluence of neutrons of a given energy distribution after which the sensitive materialwill be consumed to such an extent that the detector characteristics exceed the specifiedtolerances for a specified purpose [IEV 394-18-30]
3.1.5
capture cross-section
measure of the probability of a particular collision or interaction process, stated as theeffective area which target particles present to incident particles for that process
3.1.6
Compton effect
ordinary elastic collision in which an incident photon of energy Eo = hvg strikes a targetelectron causing the electron to recoil with energy E = 1/2mv2.the photon itself is scatteredat an angle e and energy E’ = hvo- E
3.1.7
cross-section, o
area within a target nucleus，which if struck by an incident particle will lead to a reactiontaking place. The number of particles undergoing interaction (n,) is equal to the number ofincident particles (n;) times the cross-section (o) times the total number of target nuclei pertarget volume (N) times the target thickness (t).
n, = n;oNt
The cross-section is expressed in barns (1 b= 10-28m2)
3.1.8
decay constant(a)
disintegration constant
radioisotope decay constantproportionality constant
for each radioisotope,2 is derived by dividing the natural logarithm of 0,5 by the half-life (inseconds), and expressed in s-1
A= (In0,5)/t1/2 = 0,693/t1/2
3.1.9
delayed response
time delay or lag in signal generation after exposure to a step change in neutron fluence rate.The mean lag time is (t/2/In2) where typ is the half-life of the radioisotope which producesthe signal.The signal reaches equilibrium after a period of about five times t/2 following thestep change
3.1.10
equilibrium response
for beta-decay self-powered neutron detectors, the response (signal) generated once the rateof neutron capture in the emitter equals the decay rate of radioisotopes in the emitter
3.1.11
half-life (t1/2)
time required for the number of atoms or the activity of a radioactive element to decreasefrom a particular value to half that value
3.1.12
in-core neutron detector
detector， fixed or movable,designed for the measurement of neutron fluence rate (flux) orneutron fluence at a defined point or in a region of a reactor core or primary envelope
3.1.13
integral self-powered neutron detector
self-powered neutron detector assembly in which the lead cable section is an extension ofthe detector section, i.e. the emitter is directly attached to the corelsignal wire; both sectionsshare common insulation, and the collector of the detector section is also the outer sheath ofthe lead cable section (see figure 1)
BS IEC 61468 pdf download – Nuclear power plants — In-core instrumentation — Characteristics and test methods of self-powered neutron detectors
