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3.7 Air Monitoring Programs

  • Issued: September 2014
  • Content last reviewed: September 2014

3.7.1  General Information

There were a number of criteria used in the selection of monitoring sites for air sampling. Primary consideration was given to the distribution of the local population and distance from the nuclear installation. Final site selection was based on the availability of electric power and security concerns.

The Air Particulate and Tritium-in-Air monitoring programs run simultaneously and are in continuous operation. The apparatus used in these programs while similar is quite distinct which reflects the difference in what is being monitored.

RPMS staff maintain and carry out regularly scheduled servicing of the air monitoring equipment throughout the year. Samples are collected at regular intervals from the Bruce, Darlington and Pickering Surveillance areas by RPMS staff. By agreement, samples are collected and sent to the laboratory by federal staff in the Essex Surveillance area and municipal staff in the Ottawa Surveillance area.

3.7.2  Air Particulate Monitoring Program

This program is designed to monitor for airborne emissions of fission and activation products that are distributed as particulates throughout the air. The sampling of particulates in air is a necessary component of an emergency preparedness program.

There are a total of 21 Air Particulate Monitoring Stations in operation. No new air monitoring stations have been added since 2010. A complete listing of all the Air Particulate Monitoring Stations is given in Table 2a and 2b.

Figure 1 shows a typical Air Monitoring station. The apparatus used for Air Particulate monitoring is housed in a locked louvered metal enclosure. Figure 2 presents a close-up of the electric pump, flow controller, timer, calibrated gas meter and open-faced filter cartridge that make up this apparatus. The controller has been adjusted to operate at a flow rate of approximately 7 m3/h (cubic metres per hour). Air is drawn into the enclosure by a 4.0 L/s ventilation fan. The pump exhaust is discharged outside the enclosure.

Polyester reinforced glass microfibre filters are used to capture sub-micron particulates in the air that may have radioactive isotopes attached to them. The filters possess high collection efficiency and are changed every four weeks.

Figure 1: Typical Air Monitoring Station

Typical air monitoring station, identifying tritirum-in-air Appartus and air particulate sampler

Figure 2: Close-up of Air Particulate Sampler

Close-up of an air particulate sampler identifying the air fliter assembly, gas meter and pump motor

Figure 3: Tritium-in-Air Sampler

Cells filled with slica gel can be seen in this figure along with the timer control unit.

When the filters first arrive at the laboratory, time is allowed for the short-lived daughters of any naturally occurring radionuclides captured on the filters to decay. The filters are analyzed using high purity germanium detectors and concentration estimates are determined for the gamma emitting nuclides Beryllium-7, Cesium-137 and Iodine-131.

The isotope Beryllium-7 is formed naturally in the atmosphere from cosmic ray interactions and is not associated with the effect of nuclear power generation. Determining its presence is used as a laboratory indicator. The result of this analysis is reported in μBq/m3 (microBecquerels per cubic meter).

The filters are screened for gross beta activity using a proportional counter, as not all radionuclides are gamma emitters. Two-inch diameter discs are cut from each filter in order for them to fit on the sample holder of the proportional counter. Gross beta activity is reported in mBq/m3 (milliBecquerels per cubic meter).

3.7.3  Tritium-in-Air Monitoring Program

This program is designed to monitor for tritium, an activation product in CANDU nuclear reactors.

There are 8 Tritium-in-Air sampling units currently in operation. Table 2a and 2b lists the locations of these units.

Each sampling unit consists of a 50 W electrical pump (similar to an aquarium pump) with a timed flow rate controller, a calibrated gas meter and two cylindrical cells filled with silica gel. This assembly is contained in a separate housing that is attached to the outside of the air monitoring station (see Figure 1). A close-up image of the silica gel cells is provided in Figure 3.

Low flow rates of 0.1 L/min are achieved by cycling the pump on and off for short periods. This low flow rate is needed to prevent the silica gel from becoming saturated with moisture before the end of the measurement period. The gas meter is installed to measure the volume of air that passes through the cells.

The silica gel cells are replaced at four-week intervals. The cells are weighed before being placed in the field and after they are returned to the laboratory to determine the mass of water vapour absorbed. The silica gel is placed in a tube furnace and the water vapour is desorbed by heating. A stream of dry air removes the water vapour to where it is condensed and collected. Low-level beta counting in a liquid scintillation detector is used to determine the tritium activity in the condensate. The result of this analysis is reported as Bq/m3 (Becquerels per cubic metre).

3.7.4  Air Monitoring Results

In 2012, a total of 313 environmental samples were collected. These consisted of 225 air filters for the Air Particulate monitoring program and 88 Tritium-in-Air samples. In total, 988 analytical results were obtained for the air monitoring programs. Tables 3a and 3b provide a summary of the results from the two air monitoring programs for each surveillance area.

In 2012, the results of the Air Particulate monitoring program were very consistent with those of previous years. The concentrations of the γ-emitting nuclides were consistently below the minimum detectable concentration (MDC), with the exception of naturally occurring Be-7.

The median value of the gross-β; measurements in each surveillance area was well below 1 mBq/m3.

Table 3a: Air Particulate Monitoring Results
Surveillance Area Number of Samples Be–7
Arthur 12 3350 < 80[ 1 ] < 80[ 1 ] 0.77
Bruce 34 3050 < 80[ 1 ] < 80[ 1 ] 0.86
Darlington 106 3100 < 80[ 1 ] < 80[ 1 ] 0.79
Essex County 5 2300 < 80[ 1 ] < 80[ 1 ] 0.94
Ottawa Valley 4 1100 < 80[ 1 ] < 80[ 1 ] 0.72
Pickering 47 3050 < 80[ 1 ] < 80[ 1 ] 0.77
Toronto-west 12 3150 < 80[ 1 ] < 80[ 1 ] 0.88

The median concentrations in the Tritium-in-Air monitoring program, shown in Table 3b, ranged from 0.03 to 1.60 Bq/m3. These concentrations are comparable to those observed in previous years. The larger value that is presented here is less than 0.2% of the DSC for tritium-in-air of 700 Bq/m3.

Table 3b: Tritium-in-Air Monitoring Results
Surveillance Area Number of Samples Median
Measurement (Bq/m3)
> DSC[ 2 ]
Arthur 11 0.03 0
Bruce 33 0.85 0
Darlington 11 0.16 0
Pickering 33 1.6 0

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[ 1 ] MDC for each nuclide

[ 2 ] DSC – Derived Survey Concentration

ISSN 1929-2899