BS IEC 60951-2 pdf download – Nuclear power plants — Instrumentation important to safety — Radiation monitoring for accident and post-accident conditions — Part 2: Equipment for continuous off-line monitoring of radioactivity in gaseous effluents and ventilation air
1 scope
This part of lEC 60951 provides general guidance on the design principles and performancecriteria for equipment for continuous off-line monitoring of radioactivity in gaseous effluentsand ventilation air used in nuclear power plants for accident and post-accident conditions.
General requirements for technical characteristics, test procedures, radiation characteristics,electrical，mechanical，and environmental characteristics are given in lEC 60951-1. Theserequirements are applicable in this part unless otherwise stated.
This standard is applicable to:
. noble gas activity monitors intended to measure the volumetric activity of radioactive noble
gases in gaseous effluents at the discharge point and the variation of volumetric activitywith time during accident and post-accident conditions.The monitor may also be used forthe determination of the total discharge of noble gas activity over a given period;
noble gas, aerosol and specific nuclide (commonly iodine, in its different forms: inorganiciodine,organic iodine and iodine sticking on dust) monitors intended to measure thevolumetric activity in air or gas systems (control room ventilation，reactor leakagecollection，drywell ventilation exhaust，fuel handling building ventilation exhaust，reactorbuilding ventilation purge exhaust) and detect any significant increase of radioactivityduring or after an accident.
This standard is only applicable to continuous off-line measurement, i.e. monitors whosedetector measures a representative proportion of the main effluent or ventilation stream atsome remote location (sampling assembly). lt does not apply to monitors with the detectorpositioned in or adjacent to the effluent or ventilation stream，which are within the scope ofiEc 60951-4.
Sample extraction and laboratory analysis，which are essential to a complete programme ofeffluent monitoring, are not within the scope of this standard.
Normative references
The following referenced documents are indispensable for the application of this document.For dated references, only the edition cited applies. For undated references, the latest editionof the referenced document (including any amendments) applies.
IEC 60951-1:2009，Nuclear power plants – Instrumentation important to safety – Radiationmonitoring for accident and post-accident conditions – Part 1: General requirements
IEC 61226,Nuclear power plants – Instrumentation and control systems important to safety -Classification of instrumentation and control functions
ISO 2889:2009，Sampling airborne radioactive materials from the stacks and ducts of nuclearfacilities
Terms and definitions
For the purposes of this document, the terms and definitions given in lEC 60951-1 apply.
4Design principles
4.1General
The general requirements of lEC 60951-1 are applicable to all types of monitors within thescope of the present standard, unless otherwise stated.
4.2Basic requirements related to functions
The equipment will typically measure levels of activity in engineered gaseous dischargeroutes，such as reactor or fuel handling buildings,and ventilation ducts and stacks. It isintended to provide, depending on the required function, a measure of activity discharged tothe environment or detection and quantification of leakage in containment barriers，and anyuseful information on the behaviour of the plant,which causes or allows the activity release.
The measurement of activity discharge to the environment should ideally be comprehensive,but since measurement of halogen and particulate activity released in effluents during anaccident is more complex, it is often judged that monitoring only noble gases will be sufficient.Therefore，monitors should be capable of detecting Rand measuring gaseous effluentradioactivity with compositions ranging from fresh equilibrium noble gas fission productmixtures to 10 days old mixtures. Multiple instruments may be needed to cover the effectiverange of measurements required.
Since the measurement is continuously carried out on a sample of effluent or ventilationtransferred to a remote location, the detection and measurement assembly shall be installedin an accessible location and in an environment which is compatible with the equipmentdesign limits specified in this standard.This shall be also applicable to the active parts of thesampling assembly (pumps,flow control instruments) requiring maintenance.
The other part of the sampling assembly (sampling probe, pipework) may be designed for andlocated in a harsh environment. ln this case, if the monitor is classified according to theguidance of lEC 61226, it should be classified at the same level as the monitor. lf qualificationis needed， the part of the sampling assembly located in the harsh environment should beenvironmentally qualified to these specific ambient conditions.
lf necessary，the system shall indicate a value related to the measured volumetric activityunder the conditions of temperature and pressure at the sampling location，agreed uponbetween the manufacturer and purchaser. They shall also agree on how to correct ‘theexpression of measurement if the conditions inside the measuring assembly are different fromthe calibration conditions.
4.3Sampling assembly4.3.1General
The design of the sampling assembly shall take into account the guidance of lSo 2889 andshall comply with the general requirements of lEC 60951-1.
BS IEC 60951-2 pdf download – Nuclear power plants — Instrumentation important to safety — Radiation monitoring for accident and post-accident conditions — Part 2: Equipment for continuous off-line monitoring of radioactivity in gaseous effluents and ventilation air
