New Concerns about Tritium

I must be feeling homesick because my attention keeps going back to nuclear issues in Canada that are currently getting coverage in mainstream and social media. Or I might just be sick of thinking about the Gordian knot closer to my home that is the ruins of the Fukushima Daiichi NPP.

Canada’s CANDU (heavy water) reactors have a good record of safety and don’t face the seismic and flooding risks of some reactors south of the border. They have never had a meltdown, and if they do face a serious loss of power incident, they are said to have more passive safety and be easier to cool off and contain than light water reactors.

The major concerns that have persisted over the years have to do with tritium (a radioactive hydrogen isotope) releases and long-term storage solutions for nuclear waste.

CANDU reactors release 20 times as much tritium as American light water reactors, and so it is no random coincidence that the allowable limit for drinking water is higher in Canada – 7,000 Bq/L. CANDU reactors couldn’t operate if they had to adhere to the American limit of 740 Bq/L. The actual level of tritium in the Great Lakes is close to the natural level of the pre-nuclear age (about 10 Bq/L), but what the limit means is that when a release occurs and the local water is contaminated, the government of Canada thinks that it is alright for people to consume water with 7,000 Bq/L. It seems this level was set upon the assumption that such an intake level would not last for long.

Same lake, different standards of safety on the American and Canadian sides of it.

This high level is considered to be safe because tritiated water is assumed to have a short biological half-life of about ten days. It’s water, after all. You drink it in and it is quickly sweated out or passed in urine, then replaced by the next gulp of water. But it’s not that simple. There have always been lingering questions about how much tritium becomes organically bound (OBT-organically bound tritium) and what impact OBT could have on ecosystems.

If you remember anything at all about high school chemistry and biology lessons, you might remember that H figures prominently in organic compounds, and H gets into them ultimately through the breakdown of H2O, carbohydrates, fats and proteins. This is more of a factor in plant biology because the well-known simplified equation for photosynthesis is:

So while it is true that a lot of tritium will quickly be diluted and evaporated to insignificant levels, some of it will bio-concentrate and bio-accumulate. Animals eat the sugars and carbohydrates made by the plants, and tritium can end up staying inside human tissue much longer than the presumed ten-day biological half-life. It’s important to note also that the hydrogen atoms in DNA also get there from food and water taken in by organisms. There is evidence of tritium being bound in DNA molecules.

The effects remain debatable, but the recent findings on this matter, as reported by Tap Canada, have prompted calls for a review of standards for tritium. One study of marine life near British nuclear plants found tritium concentrated at 1,000 – 10,000 times the level of the surrounding sea water. This finding, and others, prompted the French Autorite de Surete Nucleaire (ASN) to call for an investigation on new approaches in relation to "possible hereditary effects." After the publication of the ASN’s White Paper on tritium, the ASN called for a monitoring committee and for nuclear operators to control their tritium emissions. There is little comfort given by this report when it states,

“Discharges of this element are forecast to increase due to expected changes in the fuel management methods used by the NPP [nuclear power plants], and also due to new tritium-emitting facilities, including new power plants that are to be built, and the ITER [fusion energy experimental reactor]project.”

Did Ontario Power Generation get the message? It’s not like they haven’t heard it before. The concern raised by the ASN has existed ever since nuclear scientists had to start handling tritium. The International Institute for Concern for Public Health reported in 2006:

“Convinced of the dangers to health from tritium, the Toronto Board of Health and Toronto City Council have asked the Province to reduce the level of tritium allowed in the city’s drinking water. The Council then passed a resolution endorsing the 1994 ACES scientific advisory body to the Government of Ontario recommendation that the standard be reduced to 100 Bq/L immediately and then go to 20 Bq/L after five years.”

Another pressing concern in Canada is the imminent decision about long-term nuclear waste disposal. A newly formed group called Stop the Great Lakes Nuclear Dump has launched a petition drive to oppose Ontario Power Generation’s plan to build a Deep Geological Repository one kilometer from the shore of Lake Huron. The plan raises obvious questions about the safety of the water supply, the lack of public awareness of the proposal, and the suspiciously convenient location near the source of so much nuclear waste in Ontario, the Bruce Nuclear Generating Station, the largest NPP in the world measured by net power rating.

Further reading: Ace Hoffman's in-depth report on tritium.

Ian Fairlie. Radiation Risks of Tritium: Additional Notes for the Ontario Drinking Water Advisory Council (ODWAC)