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3.7.3 Monitoring during intrusive investigations

Contents Radiological Non-radiological

Monitoring is undertaken during intrusive investigations for three purposes:

  • To protect the health and safety of workers.
  • To minimise the spread of contamination.
  • To provide environmental data.
    Monitoring can be distinguished between radiological and non-radiological. Radiological

Radiological monitoring should be undertaken during all intrusive investigations where radioactive contamination may be present. In the context of this guidance, this means that radiological monitoring should be undertaken during all site investigations.
An appropriate monitoring regime for an intrusive investigation is given in Table 3.45 below.

Issue Proposed regime
Selection of appropriate monitoring equipment. * Should be determined by an appropriately trained person, such as a radiation protection advisor.
* Monitors should be selected to detect the radionuclides expected to be present on the excavation area and on the site.
* Monitors should be selected to be sensitive enough to detect the background radiation level at the excavation area.
* Monitors should be sensitive enough to ensure the safety of workers, to enable on-site screening and selection of samples and to enable waste segregation (if required).

Monitoring of the ground surface prior to excavation at that location.

* Should be carried out in addition to any previous radiological surveying works over the area, to ensure that the extent of the surface radioactive contamination is known/verified.
Regular monitoring of the excavation. * Trial pits. In trial pits, a probe can be lowered into the excavation to detect if radioactivity is present. This provides a sensitive measure of the first occurrence of radioactive contamination, which is detected before the contaminated material is excavated. (Note that the background level of radioactivity detected during excavation will alter as the excavation becomes deeper, because of geometrical effects and because different soil horizons are encountered).
* Temporary shallow boreholes. In temporary shallow boreholes used for soil sampling, an appropriate narrow diameter probe would be required for down-hole measurements. Although this would provide useful depth-dependent information with better sensitivity than could be achieved from monitoring spoil or samples, it is limited by issues such as borehole stability. Down-hole radiological monitoring is discussed further in Section 3.6.2. As with monitoring of trial pits, the background level of radioactivity may alter with depth because different soil horizons are encountered.

Regular monitoring of the spoil generated during the excavation process.

* Ensuring that any buried radioactive contamination will be detected in the spoil produced by the excavation process.
* The spoil should be monitored at regular intervals, and any changes in radiological contamination should be noted.
Regular monitoring of soils to aid in the sample selection process.

* See Section 3.6.2.
Monitoring on completion of each excavation. * Personnel should be monitored to ensure that they have not been contaminated with radioactivity.
* The ground surface around the excavation area should be monitored to ensure that it has not been contaminated with radioactivity.
* The excavation equipment should be monitored to determine if it has become contaminated with radioactivity (in which case decontamination will be required, in addition to any routine cleaning procedures taken to minimise any new cross-contamination).
* The outside of the sample containers should be monitored to ensure that (i) there is no loose surface radioactive contamination, and (ii) any external radiation levels do not present a hazard to personnel.

Monitoring on completion of the intrusive phase of the site investigation. * All equipment used in the investigation should be monitored and a radiological clearance certificate issued by the relevant health physicist.
* All samples should be monitored and issued with the appropriate documentation (e.g., a radiological clearance certificate for uncontaminated samples) prior to being transported to the laboratory.

Table 3.45 A typical procedure for an appropriate monitor regime during undertaking excavations at a nuclear licensed site
. Non-radiological

Information available in literature about this topic will be included in a later edition of EURSSEM.