Measurements

8.26.

As part of monitoring programmes, measurements may be performed at the source, in the environment and in laboratories. Monitoring at the source can be performed through on‑line monitoring or sampling and laboratory measurements. On‑line monitoring should provide a continuous indication of the activity of radionuclides in the discharge in real time or near real time and typically involves the measurement of dose rate or gross activity. Continuous flow measurement should be performed to estimate the release rates of significant radionuclides. Procedures for continuous measurement systems should include a regular schedule for instrument calibration and maintenance as well as performance checks on the analysis systems.

8.27.

Field measurements may include measurements performed in situ by gamma spectrometry; measurements of aerosols or gases at fixed monitoring stations with or without gamma spectrometry capabilities; measurements with alpha and beta monitors; measurements of dose rates; and measurements of surface contamination. Field measurement procedures should be established and validated to ensure that they are reproducible and representative of conditions at the time of sampling and deliver the necessary accuracy and precision.

8.28.

Measurements of samples in laboratories should be used to characterize the activity concentration of radionuclides in the source and the environment. For the assessment of individual doses, dosimetry laboratories should use measurements from individual dosimeters and/or bioassay samples (see Table 4).

8.29.

If monitoring data are used to verify compliance with a dose limit or a dose constraint or are compared with an operational limit or reference level, the detection limit of the analytical procedure and equipment should be selected so as to enable measurements to be made at levels that are lower than the limits or levels against which the results are to be compared. This could involve, for example, using more sensitive equipment, collecting a statistically significant number of samples, improving measurement statistics and increasing counting times. The contribution of multiple radionuclides to the total dose to the public should also be considered in the determination of a fit-for-purpose detection limit.

8.30.

The equipment to be used for measurements should be selected taking into account the purpose for which it is to be used. In particular, it should take into account the specific radionuclides that might be present, both in operational states and in accident conditions. For example, nuclear power plants might discharge a large number of radionuclides with half‑lives ranging from seconds to thousands of years, whereas fuel fabrication facilities discharge a much narrower range of radionuclides with no short lived radionuclides. Monitoring systems should have sufficient measurement range, appropriate alarm levels and flexibility to handle differences in the magnitude of the releases and the radionuclide composition.

8.31.

Table 4 presents examples of monitoring parameters and their respective sampling and measurement techniques that should be considered for different types of monitoring. Technical considerations for measurements that might apply to facilities in normal operation are presented in the Annex.

^a External dose could result from different penetrating radiations, such as photons, neutrons and high energy charged particles.

^b If discharge limits are for total alpha/beta activity, then routine analysis for specific radionuclides might not be necessary.

^c Typically measured 1 m above ground

^d For discrete samples, the sampling interval is determined on a case‑by‑case basis.