BS IEC 61031:2020 pdf download – Nuclear facilities — Instrumentation and control systems — Design, location and application criteria for installed area gamma radiation dose rate monitoring equipment for use during normal operation and anticipated operational occurrences.
b) System and equipment performing category B or C functions
Any software in the area radiation monitor performing category B or C function shall be designed and maintained in accordance with IEC 62138. Any hardware in the area radiation monitor performing category B function and including software shall be designed and maintained in accordance with IEC 60987. Hardware performing category C function in the area radiation monitor shall be designed, selected and maintained according to the supplier’s requirements.
5.3 Range of measurements
The required area radiation monitoring range shall be specified as agreed between manufacturer and purchaser. These ranges shall take into account the radiation environment of the plant design on the basis of:
— the expected minimum gamma radiation dose rate and whether it is desirable to monitor that rate,
— the expected dose rate in normaloperating conditions, and
— the expected peak dose rate under anticipated operational occurrences.
The measuring range shall normally be high enough to assure an on-scale reading for radiation dose rates up to the expected peak dose rate under anticipated operational occurrences. However, when high transient dose rates occur in areas during periods when personnel access is prevented, it may not be necessary to meet this requirement. In order to avoid false dose rate indication in this situation, the radiation monitoring system shall comply with the overload testing specified in IEC 60532.
In the event of a high transient dose rate, the instrument shall maintain on over-range indication and alarm status. It is necessary to avoid foldback” of the detector. Foldback is shown in Annex B.
Unless otherwise specified, the area radiation monitor shall at least cover the measuring range of i05 Gy/h or Sv/h to 10-2 GyIh or Sv/h. It is expected that, in most applications, a measuring range of four or five decades will be used (see Annex A). Six or more decades may be required for some special applications.
Examples of ranges of measurement of area radiation monitors in boiling and pressurized light water reactors, gas cooled reactors and sodium cooled fast reactors are given in Annex A.
5.4 Location criteria
5.4.1 General
Location criteria and safety requirements for area radiation monitors shall be appropriate to the
plant design.
Generally, they will be required at those locations which can be routinely entered by plant personnel and where one or more of the following plant conditions are identified:
a) where the dose rates are significant and may increase rapidly and without other indication:
b) where the radiation dose rate can increase sufficiently to require evacuation of personnel:
c) where occasional high radiation dose rates might preclude access at certain times:
d) where the dose rate data is required prior to personnel access;
e) where the dose rate can rapidly increase due to external operation of the controls by others. In addition, area radiation monitors may be required at locations such as access routes and plant areas where access is essential under accident conditions.
Area radiation monitors will normally be required to monitor the local radiation dose rate inside a containment building where personnel access is possible. The detector location will normally be immediately inside all entrances (personnel and equipment locks) and other locations, where regular access is required. Because periodic calibration and maintenance of area radiation monitors generally require access to the detector assembly in order to expose it to an appropriate radiation field, care shall be taken in choosing the location of this assembly so as to facilitate introduction of a suitable radiation source or field generator and to minimize radiation scatter as well as access problems to the equipment to be calibrated. The detector location shall be chosen, as far as is consistent with the required monitor function, in order to avoid adverse environmental conditions and significant levels of electromagnetic interference.