IEC 60761-3:2002 pdf download

IEC 60761-3:2002 pdf download.Equipment for continuous monitoringof radioactivity in gaseous effluents -Part 3: Specific requirements for radioactivenoble gas monitors.
3 Terms and definitions
For the purpose of this part of IEC 60761, the following definition applies.
3.1
radioactive noble gas monitor
equipment designed for the Continuous monitoring of radioactive noble gases in gaseous effluents discharged into the environment
4 Classification of radioactive noble gas effluent monitors
The equipment may be classified according to the type of radiation detected as:
— gamma;
— beta;
— specific nuclides.
It may also be classified according to the method of operation:
— direct measurement with a detector in or adjacent to the effluent;
— continuous fractional sampling of a monitoring point at a remote location.
5 Overall equipment design
As mentioned in IEC 60761-1, various monitor configurations are possible, depending on the exact circumstances and requirements for each installation. Irrespective of these variations, the equipment shall conform to the requirements of this standard as well as those of
IEC 60761-1.
5.1 Direct measuring equipment
If the measurement is made directly by detectors in or adjacent to the effluent stream, only the detector and the minimum necessary electronic assembly shall operate in these environmental conditions. Unless there are special circumstances, this type of equipment shall not incorporate detectors which are particularly sensitive to variations in environmental conditions or require frequent attention or adjustment.
The appropriate control and measurement assembly should be mounted, wherever practicable, in a controlled environment, so as to minimize the effects on performance and allow ready access for operation and maintenance.
5.2 Indirect measuring equipment
If continuous representative samples of the effluent are taken to a remote location, the sampling and detection assembly (with the exception of the sampling probe and pipework) and the control and measurement assembly should be adjacent in a controlled environment. Where this is not practicable (for example because of the excessive length of the sampling pipework involved), the same restrictions as for a detection assembly (as per 5.1) shall be applied in order to ensure a rapid response to any increase in radioactive content.
A by-pass system should be provided, if practicable, to facilitate maintenance and functional testing on the detection and sampling assembly
6 Expression of measurements
In accordance with the requirements of clause 9 of IEC 60761-1. the electronic assembly associated with the detector shall provide a reading expressed in appropriate units.
If readings have to be provided in derived units (e.g. Bq/m3), the manufacturer and purchaser shall be confident that all the relevant factors are understood and are either constant or corrected automatically.
7 Sampling and detection assembly
7.1 SamplIng and exhaust pipes
In addition to the general requirements, the following characteristics shall be considered and agreed upon:
— the impact of the flow-rate and the pressure drop on the measurement;
— the delay time to detector (flow-rate, pipe diameter, etc.).
7.2 Inlet device
An appropriate device shall be placed at the sampling circuit inlet to remove any particulates and iodine, when necessary, from the air. In order to maintain the specified performance of the assembly, such a device shall not trap or even temporarily retain noble gases and decrease the flow-rate.
In addition, appropriate shielding shall be provided for personnel protection and to limit the effect on the detection assembly of the radiation from activity accumulated on the device during the sampling period. The device shall be accessible and its operation controlled.
It should be noted that iodine isotopes are decay precursors of noble gases. It is therefore required that, whenever an iodine filter is provided in the inlet circuit of a monitor, an analysis be performed to demonstrate that the iodine retained on the filter does not result in a false estimate of the time profile of the noble gas release.
7.3 Sample cell
Where, as part of a sampling and detection assembly, a measuring cell or gas chamber is used to provide a volume of gas for measurement with an immersed or adjacent detector, the following requirements shall apply:
— The sample cell shall be of the flow-through type. It could include an absorbing medium or pressurizing facility.