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Although TRIUMF does not have a nuclear reactor, the lab has been following the evolving story of the global efforts to manage the nuclear-power plant situation in Fukushima, Japan, after Friday, March 11's earthquakes and tsunamis.
Some of the most useful references to understand the situation are as follows:
Canadaian Health & Safety
Potential Public-Health Risk to BC Judged Minimal
CNSC and Health Canada have judged the public-health risk from radioactive material blowing over the Pacific to British Columbia and Western Canada to be quite minimal. This can be understood using some rough calculations as summarized below by Dr. Anne Trudel, TRIUMF's manager of environmental health and safety.
Concern over the exposure from possible releases of radioactivity from the Japanese reactors in Fukushima is understandable. It is important however to put the risk in context for us here in Vancouver. The dose to a Vancouverite from a release in Japan will depend on the magnitude of the release, the wind direction, and the dilution from atmospheric dispersion across the Pacific Ocean. Although every sign indicates that the total quantity of releaed radioactive material released from the Daiichi reactors will be much less than that of the Chernobyl incident, we can use that value as an absolute maximum.
A Becquerel (Bq) is a measure of the quantity of radioactivity, defined as the quantity of radioactive material that results in one radioactive decay per second. Radioactive material dispersed across an area is sometimes measured in terms of Bq per square metre or Bq/m2. A Sievert is the quantitative unit used to evaluate the biological effect of ionizing radiation.
With the wind blowing towards the east, we would expect the downwind dispersion from Fukushima to result in significant dilution. Using concentrations of one hundred times less (400 Bq/m2) in Vancouver (7,500 km from Tokyo) than what was seen at 200 km from Chernobyl (40,000 Bq/m2) is conservative. The first exposure to a Vancouverite would be from radioactivity wafting by in the air, followed by potential exposure from ingesting radioactive material after it settles onto surfaces such as soil or plants.
With the modeled level of soil contamination above, the annual external exposure would be 0.0000000013 Sv (or 1.3 nano-Sieverts or 1.3 billionths of a Sievert) and the exposure from consuming fruits and vegetables grown on this land would be 0.0000011 Sv (or 1.1 micro-Sieverts or 1.1 uSv or 1.1 millionths of a Sievert). The assumptions made in obtaining these values are that all the produce consumed in one year is grown on this contaminated soil, and for the external dose a correction was made for the building shielding for the fraction of time spent indoors. The total dose is dominated by that from ingestion of contaminated produce and amounts to 1.1 uSv (micro-Sieverts).
Recalling that the dose we receive from background radiation annually is 0.002 Sv (or 2 mSv), this very conservative estimate for annual exposure to fall-out amounts to about 1/2,000 of our ordinary annual background exposure. Dose rates from exposure to iodine contamination would be similarly low. ( Iodine-131 is more radiotoxic than Cesium-137 but it has a much shorter half-life.) There is also natural radioactivity in vegetables from Potassium-40 and Carbon-14. There is therefore no reason for people in Vancouver to limit their consumption of foods grown here or to take potassium-iodide tablets. In fact an over consumption of potassium iodide is a risk to health.
An excellent visual resource for understanding these levels of dose and exposure is available here. Some other numbers that are useful for putting dose in context are (a mSV is one-thousandth of a Sv; a uSv is one-millionth of a Sv):
Recent reports (Mar 28) have discussed the levels of radiation detected in Fukushima as well as in BC in terms of Bq per square metre of land area (Bq/m2) or in terms of Bq per Litre of water (Bq/L). These values measure the degree of radioactivity distributed or dispersed across a surface or dissolved in a fluid. The recent measurements by TRIUMF collaborators at SFU are quite benign. For instance, in the unlikely case that one drinks pure, unfiltered rainwater, one would need to drink ~4,500 litres to get a dose of 1.2 mSv (roughly, the yearly background radiation in Vancouver) at the maximum reported concentration. That means >12 litres/day, every day, for 1 year, of rainwater collected from th