Human Health and the Biological Effects of Tritium in Drinking Water Douglas Boreham, Professor McMaster University Medical Physics and Applied Radiation Sciences, Hamilton, Ontario, Canada. Principal Scientist, Bruce Power.
McMaster and Bruce Power AECL - CRL McMaster
Basic CANDU Operation • CANDU’s (CANadian Deuterium Uranium) reactors use heavy water in the primary heat transport system (the coolant) and as a moderator of the nuclear reaction Antoniazzi August 26, http://en.wikipedia.org/wiki/CANDU_reactor 2010
Environmental Monitoring Bruce Power 2009 Tritium in Drinking Water 50.0 40.0 Bruce A 30.0 /L Bruce B Bq 20.0 proposed 20 Bq/L Approx. Minimum Detection 10.0 0.0 y y ril y ne uar rch Ap Ma July gust ber ber er Ma Ju tober Januar Au em Febr Oc vem ecemb Sept No D Month
Radiological Environmental Monitoring Tritium in Drinking Water 2001-2009 50 45 40 35 30 /L 25 Bq 20 15 10 5 0 y r r r r r r r r r r r r r r r r r r ry h t t t t ril y ly t y ry h ril y ly t y ry h ril y ly t y ry h ril y ly t y ry h ril y ly ts y ry h ril y ly s y ry h ril y ly s y ry h ril y ly s y ry h ril y ly s rc s be ber ber rc s be ber ber rc s be ber ber rc s be ber ber rc be ber ber rc be ber ber rc be ber ber rc be ber ber rc be ber ber ua une une une une une Ap Ma une une une une J Ju m tobe ua Ap Ma J Ju m tobe ua Ap Ma J Ju m tobe ua Ap Ma J Ju m tobe ua Ap Ma J Ju m tobe ua Ap Ma J Ju m tobe ua Ap Ma J Ju m tobe ua Ap Ma J Ju m tobe ua Ap Ma J Ju m tobe anuar br Ma ugu e c em em anuar br Ma ugu e c em em anuar br Ma ugu e c em em anuar br Ma ugu e c em em anuar br Ma ugu e c em em anuar br Ma ugu e c em em anuar br Ma ugu e c em em anuar br Ma ugu e c em em anuar br Ma ugu e c em em J e A e A e A e A O J e A O J e A O J e A O J e A O J e A O F O J O J O J ept ov ec F ept ov ec F ept ov ec F ept ov ec F ept ov ec F ept ov ec F ept ov ec F ept ov ec F ept ov ec S N D S N D S N D S N D S N D S N D S N D S N D S N D 2001 2002 2003 2004 2005 2006 2007 2008 2009 Background + Past Emissions Kincardine Port Elgin Southampton Background
Recommendations 1. The Ontario Drinking Water Quality Standard for Tritium should be revised to 20 Bq/L, recognizing that: • 20 Bq/L relates to health effects from long term, chronic exposure over a life time of exposure of 70 years; • 20 Bq/L is within the range of variations considered by the council (7 Bq/L to 109 Bq/L), for a 10-6 risk level; and • 20 Bq/L, based on a running annual average, is achievable in drinking water, without significant cost to the nuclear power industry, according to the Canadian Nuclear Association.
Tritium, Heavy Water & CANDU •Heavy water is used in the CANDU reactor to control the nuclear reaction using natural uranium •Heavy water in the presence of the neutrons (capture by deuterium atom) continuously generates tritium (DTO). •Production rate ~2 x 1012 Bq/MW(e).a in the heat transport (PHT) system and ~7.2 x 1013 Bq/MW(e) in the Moderator (~97% generated in the moderator) Antoniazzi August 26, 2010
Deuterium Heavy Water and Tritium
Biological Half-Life Heavy Water (D2O) First Human Isotope Tracer Experiment (Tea Cup) • 55 samples of urine and other excreta • 1000 distillation operations Conclusion :body’s water turned over every 9 days Hevesy, G. and Hofer, E. Elimination of water from the human body. Nature 134: 879; 1934
What is Bq/L (beta Emitters) Water Tritium – Naturally 1-7 Bq/L Banana Smoothie Potassium – 40 100-150 Bq/L Veggie Shake Carbon – 14 200-300 Bq/L
Natural Radioactivity in Your Body Uranium alpha particles 90,000 per day Tritium beta particles 2,000,000 per day Potassium beta particles 3 billion/day Nuclide Total Mass of Nuclide Total Activity of Nuclide Found in the Body Found in Body Uranium 90 µg 1.1 Bq Thorium 30 µg 0.11 Bq Potassium-40 17 mg 44,000 Bq Bq is a decay per second Radium 31 pg 1.1 Bq Carbon-14 95 µg 20,000 Bq Tritium 0.06 pg 23 Bq Polonium 0.2 pg 37 Bq
Radiation Dose (2L per day x 365 days) 70,000 Bq/L = 1.0 mSv/a (Australia) 7,000 Bq/L = 0.1 mSv (Canada) 20 Bq/L = 0.0003 mSv/a (Ontario)
What is Bq/L and Dose 70,000 Bq/L = 1.0 mSv per year = 1 mammogram (2.0 mSv/yr – 200+ mSv is natural) 7000 Bq/L = 0.1 mSv per year = Standard X-ray 70 Bq/L = 0.001 mSv = Human (7000 Bq) 20 Bq/L = 0.0003 mSv = 3 minutes flying/change in 6 feet of elevation.
Radiation Tracks and Biological Cells At low dose the density of radiation ‘tracks’ is low; some cells are ‘hit’ and others are not. The radiation energy deposited in any individual cell is a random variable and covers a range that depends on the radiation type.
What are the Event Frequencies for Tritium The average dose per hit for a spherical volume 5µm in diameter (approximate diameter of a mammalian cell nucleus) from the experiments of Ellet and Braby δ = 11.2 mGy
F1 = [1-e-D/δ ]
For a tritium concentration of 20Bq/L the committed dose
is 0.286 µGy and therefore the fraction of exposed cells with hit nuclei is:- 2.5 per 100,000 cells
Sleeping next to someone most nights of a year results in a radiation dose about the same as that from an X-ray of your hand. 0.02 mSv/a = Potassium-40 X-ray
Same Dose Rate per Hour (0.004 mSv/h) = 60 hours = 0.24 mSv 30,000 ft 1 metre
0.0001 0.0004 0.1 1.0 10 500 Dose (mSv/yr)
Public radiation dose Frank Saunders
French Academy Vs BEIR
Pacific Basin Nuclear Conference Position Statement
Pacific Basin Nuclear Conference Position Statement •The risk of cancer generation is trivial or zero up to more than a hundred times the average of natural background radiation. •There are adaptive responses to low levels of radiation exposure which reduce the effects of damage from all causes, including those from radiation, thus reducing risk to levels lower than those observed in the absences of the radiation exposure.
In Press: Radiation Protection Dosimetry 2010. “Recent radiological studies in the low dose region demonstrate that the mechanisms of action for many biological impacts are different than those seen in the high-dose region. When radiation is delivered at a low dose rate (i.e. over a longer period), it is much less effective in producing biological changes than when the same dose is delivered in a short period. Therefore, the risks due to low dose-rates effects may be over-estimated.”
Implications for Radiation Protection At low dose • Dose is NOT a surrogate for risk • Dose (risk) is NOT additive and risk can increase OR DECREASE • Risk per unit dose is NOT constant, dose thresholds exist, for overall risk and for each tissue (W ) T
CONCLUSIONS At low doses • The assumptions of the LNT hypothesis and radiation protection practices are not compatible with the observations in vitro or in vivo •• Human and environmental risk assessments must consider real effects • A new approach to radiation protection at low doses is needed