Can anyone explain to me why this would be preferred over the alternative they mention in the article of evaporating the water?
From the perspective of the people releasing the radioactive water, evaporating it would give them larger volumes of a material that is more difficult to manage before it disperses and in medium where more of the radiation reaches further.
Seems like the main environmental concern ought to be absorption into tissues though, and it's not at all clear to me that highly active marine ecosystems with long food chains is the preferable alternative there.
Tritium is also produced in heavy water-moderated reactors whenever a deuterium nucleus captures a neutron. This reaction has a quite small absorption cross section, making heavy water a good neutron moderator, and relatively little tritium is produced. Even so, cleaning tritium from the moderator may be desirable after several years to reduce the risk of its escaping to the environment. Ontario Power Generation's "Tritium Removal Facility" processes up to 2,500 tonnes (2,500 long tons; 2,800 short tons) of heavy water a year, and it separates out about 2.5 kg (5.5 lb) of tritium, making it available for other uses.[13]
you dont really want to just "evaporate the water" but "distill" it, same as making alcohol... the boiling points are very close and it is expensive to process that much water.
Would love for a nuclear or environmental researcher to fact-check me here. I'm out of my depth. I'm just applying the trivia that I know.
The vast majority of water molecules in the oceans have never been drunk by any human ever.
Interesting. My source re: beta radiation was (admittedly a nuclear promotion nonprofit) http://nuclearconnect.org/know-nuclear/science/protecting
> β BETA – can only be stopped after traveling through about 10 feet of air, less than 2 inches of water, or a thin layer of glass or metal. Additional covering, for example heavy clothing, is necessary to protect against beta-emitters. Some beta particles can penetrate and burn the skin.
I won't be surprised if you're right, but if a nonprofit getting government grants to promote the nuclear industry gets it wrong, I'd be pretty worried.
The nonprofit isn't wrong... they're just saying "a .22 bullet can kill you" while parent is saying "tritium is like throwing the bullet instead of firing."
[1] https://sciencedemonstrations.fas.harvard.edu/presentations/... [1] https://en.wikipedia.org/wiki/Tritium
Electrons can deposit energy in two ways: one is by bremsstrahlung, which is basically EM radiation (X rays, usually) emitted during a fast deceleration caused by another ion; or by ionising neutral atoms and breaking bonds. Bremsstrahlung is only significant at much higher energies, so this leaves ionisation. The energy lost per unit length (-dE/dx) depends on the electron energy and can be computed using the Bethe-Bloch formula. Integrating this quantity yields the particle range R = ∫_E₀ ⁰dE (dE/dx)⁻¹.
An empirical formula that can be derived from this is the following:
R = 1/ρ 0.44cm E^(1.265 - 0.0954 log(E))
Beta radiation just describes a certain kind of radiation, namely emitting an electron (or positron). However it doesn't directly tell you how much energy that electron has.
Wikipedia on Beta particles says that "Beta particles with an energy of 0.5 MeV have a range of about one metre in air; the distance is dependent on the particle energy." [1] Tritium beta decay just has an energy of 0.018590 MeV [2] and I wouldn't be surprised if reach isn't proportional but for example cubic (I don't know the formula) thus the huge difference in reach.
[1] https://en.m.wikipedia.org/wiki/Beta_particle#:~:text=Beta%2....
Some argue we are not good enough at these things, meaning harm will come to us every time we generate energy this way. The only real question being us or future people, near or longer term harm.
Say we set that aside as a matter of ambiguity and just focus on type of harm. (My own take is we will generate energy this way, so we may as well fund serious risk mitigation of all kinds.)
We have only one option here longer term, and that is dilution.
Normally, we have two, the other being containment. (And, given we do make energy this way, strong investment in containment makes a lot of sense.)
And in this scenario, we have both contaminated water to deal with and a core likely to enter the water cycle itself at some point too. It will, at that time, irradiate water for a long time.
Is the harm in the atmosphere greater than in water?
It will go somewhere. IMHO, the water is a better shield and has far greater capacity to serve as a medium to dilute in than the air does.
First, water itself acts as an absorbent of the emitted radiation. So the only living things which take up the radiation are those which consume the water.
Second, unlike heavy metals, the uptake of heavy water isn't especially driven by biology. They don't soak up and concentrate the radiation.
Third, there is a lot more water in the ocean than the atmosphere. In the ocean it will dilute to nearly unmeasurable levels. In the atmosphere it will fall back down as rain and concentrate in our water supply, irrigation, and crops.