IEC 60951-4 pdf download – Nuclear power plants – Instrumentation important to safety – Radiation monitoring for accident and post-accident conditions – Part 4: Equipment for continuous in-line or on-line monitoring of radioactivity in process streams

IEC 60951-4 pdf download – Nuclear power plants – Instrumentation important to safety – Radiation monitoring for accident and post-accident conditions – Part 4: Equipment for continuous in-line or on-line monitoring of radioactivity in process streams
4Design principles
4.1General
Except where otherwise specified,all the requirements specified in Clause 4 of lEC 60951-1shall be carried out, unless otherwise stated.
4.2Basic requirements related to functions
The main purpose of equipment for continuous in-line or on-line monitoring of radioactivity inprocess streams is to continuously measure radiation levels in appropriate pipes or tanks,either by being positioned in them (i.e. immerged in the process stream) or adjacent to them(i.e. viewing straight through the process stream). These radiation measurements aredisplayed locally and/or in control rooms to keep plant operators aware of current radiologicalconditions. This information is used for control purposes and/or initiation of protective actions.Therefore，the equipment concerned by this standard is capable of actuating alarms andproviding inputs to other plant systems and processes in order to isolate processes atabnormal radiation levels.
The basic requirements for the design, selection, testing, calibration and functional location ofequipment for continuous in-line and on-line monitoring of radioactivity in process streams areplant specific. Process radiation monitors within the scope of this standard can be classifiedinto two basic types:
– in-line monitors: the detector is located directly in the process stream (pipe，tank, duct),- on-line monitors: the detector faces directly the process stream.
For the purpose of critical data collection，these monitors may be designed to withstandadverse environmental and seismic conditions, during and after an accident.
In addition to the basic requirements of IEC 60951-1，the specification procedure shouldinclude the following:
Establish the required measurement characteristics (purchaser): Determine the streamcharacteristics (physical， chemical and dynamic characteristics of the stream to bemonitored) such as: type of fluid,thermodynamic state，temperature range and rate ofchange, pressure range and rate of change,radiochemical properties,etc.
4.3 Range of measurement
ln addition to 4.2 of lEC 60951-1, the following requirements shall apply:The effective range of measurement should be at least six decades.4.4 In-line detectors mechanical features
4.4.1General requirements
Whenever in-line detectors are located in a sleeve or a piping system implanted as part of apipe or tank under pressure or carrying hot or corrosive fluid，specific requirements shallapply to ensure thermodynamical and mechanical conditions are taken into account.
When specified，the sleeve or piping system,including all accessories,shall be supplied bythe detector manufacturer and fully assembled on the main pipe or tank when possible.
The sleeve or piping system shall be designed and arranged to permit an easy removal of thedetector for maintenance and cleaning. The detector shall be adequately installed in thesleeve or piping system to prevent damage due to vibration under normal operation andmaintenance activities.
The mechanical features of piping and its connections，including bolting and sealing, shall beagreed between the purchaser and manufacturer,and shall conform to relevant standards.
4.4.2Pressure-containing parts
The maximum allowable working pressure of the detector at the most severe operatingconditions shall be clearly defined by the manufacturer. In no case shall the maximumallowable working pressure of the detector and the sleeve exceed that of the sleeve flanges.
Pressure casings including the detector housing shall be of such thickness as will be suitablefor containing pressure and limiting distortion under the maximum allowable pressure at theoperating temperature.
The casing shall also be suitable for the hydrostatic test pressure at ambient temperature.
The pressure-containing parts shall be made of non-corrosive materials， to be agreed uponbetween the purchaser and the manufacturer.
The bolting selected (property class) shall be adequate for the maximum allowable workingpressure of the detector sleeve and for normal tightening procedures. lf at some point it isnecessary to use a fastener of special quality, interchangeable fasteners for other joints shallbe of the same quality.
4.4.3Materials
The materials used for pressure-containing parts shall be suitable for the fluid to bemonitored. In particular，they shall resist corrosion caused by the liquid handled and byenvironmental conditions.
Materials are selected by the purchaser. lf the detector manufacturer considers othermaterials to be more suitable，these should be offered as alternatives by the manufactureraccording to the operating conditions specified on the data sheet.
For hazardous liquids, the manufacturer shall propose suitable materials for agreement by thepurchaser.
For high or low temperature applications，the detector manufacturer shall give dueconsideration to mechanical design.