Tritium, also known as radioactive hydrogen, is an isotope that releases an 18 Kev beta particle. The isotopic half life is about 12 years.
Among other possible production mechanisms, it is produced in low quantities and concentrations in any reactor where water is exposed to a neutron flux. The production rate is higher in heavy water reactors because the deuterium (H-2) that is a major constituent of heavy water only needs to absorb one more neutron to turn it into tritium (H-3). Its absorption cross-section is not very large, but there is no loss term in the build up equation.
Over the years, there has been a great deal of ink spilled in articles, reports, and legal proceedings regarding the potential impacts of releasing tritium to the environment. The stimulus for this post is an article by David Biello dated February 14, 2014 titled Is Radioactive Hydrogen in Drinking Water a Cancer Threat? .
Aside: Yes, I know. That article is more than a year old. I didn’t look at the date until I began writing this post. Apparently SciAm is doing what I occasionally do here, which is to repurpose existing content. Here is a quote of the note at the top of the article “This article is from the In-Depth Report 4 Years after Fukushima.” That in-depth report was published this year, not last. End Aside.
You might want to read the original article to obtain more context for the comment that I’ve reprinted below.
It is disappointing to read an article in Scientific American that provides such a scientifically inaccurate description of the way that the beta particles from tritium (free moving electrons that are only slightly accelerated compared to those produced in a normal electrical circuit) react with matter.
Those electrons do not “slam into DNA, a ribosome or some other biologically important molecule.” They interact with the electrons in all of the matter that they pass through, including air and water. Even in air, beta particles from tritium decay travel a MAXIMUM distance of 6 mm.
In more dense material, like biological matter, they travel a substantially shorter distance.
Living cells are composed primarily of water. DNA and other biologically important molecules are a small portion of the total mass. Most of the energy in the slow moving beta from tritium gets shared with the electron clouds of other molecules through inelastic collisions and the Bremsstrahlung effect, which turns the kinetic energy of the beta emission into electromagnetic radiation. That is the same kind of radiation that surrounds us in our modern, electrified lives.
The other important feature of tritium is that it is an isotope of hydrogen, one of the most common elements in our environment. When you mix tritium with water, the isotope inherently mixes with all other hydrogen isotopes, resulting in an irreversible dilution.
Anyone with any reasonable understanding of physics will know that a mixture of isotopes of the same element is nearly impossible to separate into the constituent isotopes without the imposition of a great deal of energy and some pretty fancy technology.
No natural biological process has any means of concentrating tritium once is is released into an environment full of other hydrogen isotopes.
It is absurdly amusing to read the following, knowing how much money has been wasted over the years in futile attempts to remove tritium from water to “protect” people against a non-existent threat.
“You need huge study populations to have any chance of seeing anything,” Kocher notes, and that money is simply unavailable. “There is no compelling need to spend the money required to do this.”
If there is no compelling need to spend money to find out that tritium at the concentrations that can possibly be accessible to humans is not hazardous, then there is no compelling need to spend money to attempt to capture it or separate it from water.
Let dilution be the solution to this particular phantom worry.
Of course, the money that has been spent on various solutions to the non-problem of tritium has been “revenue” for a large number of parties who are interested in maintaining or tightening the existing regulations. Instead of looking to variations in state rules, I wish the author had turned to our northern neighbors to find out that their drinking water limit is 10 times higher than ours or to Australia to find out theirs is 100 times higher.
In neither case is drinking water full of tritium at the limit dangerous to human beings.
Publisher, Atomic Insights
There is a large, expensive, and worrisome tank farm full of tritiated water on the site of what used to be the Fukushima Daiichi Nuclear Power station. That tank farm is complicating the process of cleaning up the site. The most logical, lowest cost solution is to simply empty the tanks into the adjacent sea and to recycle the materials used to construct the tanks into something more useful.