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Monitoring Canadian Nuclear Power Plants
The Canadian Radiological Monitoring Network (CRMN) and laboratory facilities are operated by Health Canada to provide Canadians with accurate health assessments regarding existing levels of radioactivity and nuclear/radiological accidents from a national perspective. The CRMN is managed by the Radiation Surveillance and Health Assessment Division (RSHAD), Radiation Protection Bureau (RPB).
Measurements near Nuclear Power Plants
The network established for monitoring in the vicinity of Canadian nuclear power plants consists of sampling equipment to measure tritium in atmospheric water vapour, and thermoluminescent dosimeters (TLDs) to measure external gamma dose rate. All Canadian nuclear generating stations use the 
CANDU (CANada Deuterium Uranium) reactor.
Monitoring Sites and Results
Tritium is produced naturally by cosmic rays, but is also a by-product of CANDU nuclear reactors. Atmospheric water vapour is sampled monthly for tritium determination. The sampling equipment consists of a tritium cell, containing molecular sieve material that absorbs water vapour as air is drawn through the cell, a flowmeter and a pump. The water vapour is recovered in the laboratory, and the tritium measured by liquid scintillation counting. The flow rate of air through the tritium cell is reduced during the summer, from 0.2 to 0.07 m3/day, to prevent the sieve from becoming saturated through high humidity.
Tritium Sampling Station
External gamma dose rate monitoring is conducted using lithium floride (LiF) TLDs deployed for periods of three months and returned to the laboratory for analyses. External dose rate measurements are given in nanograys (nGy) per hour for Dose Rate and milligrays (mGy) for Cumulative Dose. Each tritium sampling site contains a TLD for external gamma dose rate monitoring.
The values reported for tritium activity and gamma dose rate are orders of magnitude below what would constitute an effective dose limit of 1 millisievert/year (mSv/year) (radioactivity and dose units) to the public.
History of Reactor Measurements
Tritium monitoring was started in 1971, around the Pickering Nuclear Generating Station. The program was expanded to the vicinity of 5 nuclear facilities; Darlington, Bruce and Pickering, Ontario, Gentilly, Quebec and Point Lepreau, New Brunswick. Collection of atmospheric water vapour for tritium analysis was discontinued in the vicinity of Bruce, Darlington and Pickering nuclear generating stations in March 1996, as a result of extensive tritium monitoring that is performed by the Ontario Ministry of Labour (OML), Radiation Protection Services.
The current reactor monitoring network consists of sites in the vicinity of Gentilly (5 sites) and Point Lepreau (6), and a new site in the Greater Toronto Area (GTA). This site was added in June 1996 to maintain a sampling site location in the GTA. The Ottawa site, located on the roof of RPB, was added in 1991 to act as a test-bed site, and to monitor background tritium levels.
The measurement of external gamma dose rate was initiated in 1976. A calcium fluoride:manganese (CaF2:Mn) bulb was used as the TLD device until 1989. In 1989, the system was changed to the Harshaw TLD-100 and LiF chips were deployed, which are more economical, easier to measure, and less subject to fade than the bulbs. Results are presented for tritium and TLD measurements for the nuclear power plants discussed above. Note that the site numbers given for these locations are not continuous. This reflects the addition and deletion of sites to the reactor monitoring network.
Other Monitoring Agencies
Other agencies monitor tritium in atmospheric water vapour and other media: OML, and the Bedford Institute of Oceanography, Department of Fisheries and Oceans, Maritimes Region (Point Lepreau Generating Station). In addition, the nuclear power plants are required to have programs in place to monitor all releases of radioactive material from their plants. This requirement is enforced by the Canadian Nuclear Safety Commission (CNSC), an independent agency of the Government of Canada, which regulates nuclear power plants.
