Why is “heavy water” used in nuclear energy, are not potable to drink, even it’s just 1 molecule more than H2O?
In: Chemistry
That extra neutron in the deuterium makes it twice as heavy as a normal hydrogen atom. A lot of biological processes depend on hydrogen having a certain mass so that, when the weight is off, they go wrong. Usually, the water we drink only has 0.03% deuterium in it, so the occasional process acting off can be offset by the majority of others that are working correctly. Drinking heavy water, which only has deuterium attached to the oxygen atoms, will add way too much into your body for natural error correction to account for.
You can drink a glass of it and it almost certainly won’t harm you. If you have inner ear issues or low blood pressure, then a glass or two might lead to dizziness. If you drink it exclusively, it’ll mess you up. But in small quantities, it’s no big deal.
Heavy water does not have any more molecules of H20. A molecule of H20 is just the smallest possible unit of water. More molecules just means you have more water. Heavy water is water where the hydrogen atom has an extra neutron. It’s still water, because it’s 2 hydrogen atoms and an Oxygen atom, and the extra neutron doesn’t change the hydrogen chemically. It weights more though, because of the extra particle… so we call it heavy water.
It’s used in nuclear energy because it’s a good neutron moderator. A neutron that is moving very fast tend to not be absorbed well – you want slower neutrons, as they are more readily absorbed , which is what needs to happen for fission (and a chain reaction) to occur. Heavy water does a good job of [slowing down neutrons](https://en.wikipedia.org/wiki/Neutron_moderator) without absorbing them.
The heavy hydrogen in water inhibits cell division in mammals, so it’s toxic. But, you need drink a lot of heavy water for it to become a problem.
Heavy water doesn’t contain an extra molecule, water is a molecule. Heavy water contains an extra Neutron in at least one if its hydrogen atoms.
Heavy water or D2O is a water molecule where one of the atoms of Hydrogen is Heavy Hydrogen or Deuterium (hence the D in D2O).
Deuterium has 1 extra neutron compared to Protium (basic hydrogen) that contains no neutrons.
1 molecule in 3,200 of water is D2O, meaning that much of your body and the water you drink is D2O and you wouldn’t be aware of it unless someone told you.
Drinking large quantities of D2O for a prolonged period can cause dizziness and low blood pressure, but this is highly unlikely outside of a lab setting.
Heavy water is used as a moderator in some reactors because it slows down neutrons effectively and also has a low probability of absorption of neutrons.
Its not 1 molecule more.
A water molecule consists of 2 hydrogen and 1 oxygen atom. Hydrogen is a atom consisting of normally just one proton.
In heavy water you still have hydrogen atoms with just 1 proton (called protium). However there is one additional particle in the atom nucleus, called a neutrons. Neutrons have the same mass as an proton but no charge and basically glue together the atom nucleus (if the fraction of neutrons to protons is wrong the nucleus is unstable and can undergo radioactive decay) but don’t change the element.
For most elements the atoms with different number of neutrons (these are called isotopes), the chemical properties are pretty similar. However as hydrogen is so light (the standard hydrogen has a mass of 1), adding a neutron makes it twice as heavy (the deuterium in heavy water has a mass of 2).
And this large mass difference of deuterium changes some chemical properties of the molecules made out of deuterium compared to the ones made out of protium (even though both are still hydrogen).
These different chemical properties make heavy water somewhat toxic to many orgasims.
In details its much more difficult to split off hydrogen ions from a heavy water molecule than on a normal water molecule. But that is something many biological processes require. Heavy water slow downs these necessary processes in a living organism, which can kill it.
H2O is the molecule (two hydrogen atoms, one oxygen atom). That is true for ordinary hydrogen, for the deuterium in heavy water, and for tritium. The distinction is in the number of neutrons in the hydrogen nucleus — none for most hydrogen, one for deuterium, two for tritium.
Tritium is already radioactive. We’ll set that aside, although you could have super-heavy or tritiated water and that would pose the additional radiation problems.
Heavy water, meaning the water with the deuterium form of hydrogen, can disrupt some biological processes that are reliant on fine-tuning at the molecular level, because of the significant difference in the weight of the hydrogen caused by adding the neutron. With most isotopes of heavier elements, this is not an issue because the addition of one or two neutrons is insignificant next to the overall mass of the nucleus; but with hydrogen, going from one proton to one proton plus one neutron is a significant mass difference. It can disrupt cell division, cause problems with bone marrow and the digestive tract, or even cause sterility and death in extremely high levels.
Unless you are intentionally setting out to live off the heavy water stored at a nuclear plant, however, this is not really a serious concern. You would have to drink quite a bit of heavy water before the level in your body became high enough to start making you seriously ill. There is actually already a very small proportion of hydrogen atoms in nature that are deuterium, so a tiny fraction of the natural water you drink is already heavy water.
Heavy water is used in nuclear energy as a moderator. Nuclear reactors run by neutrons hitting uranium-235 atoms causing them to split and release more neutrons. It is very important that enough of these neutrons hit more atoms to sustain the reaction. Heavy water slows down the neutrons which increases the likelyhood of them intereacting with a uranium 235 atom.
Why is not potable to drink, heavy water messes with the chemical reactions involving water because it’s slightly different in mass , a large enough dose makes that toxic. It is not 1 molecule different, it’s 1 neutron. Just a slight correction.
> 1 molecule more than H2O?
If you look at periodic table of chemical elements, difference by mere few electrons can turn things into insanely *different something else*. Like from light gas into heavy metal, from something relatively harmless to something quite radioactive or toxic, and so on.
That’s how chemistry works. Just adding one more oxygen atom to water molecule would turn it from very safe liquid into quite fatal and skin-irritating hydrogen peroxide. Same with heavy water.
O2 is breathable oxygen and O3 is ozone and it’s just one atom away, and you for sure can’t breathe ozone.
H2O is water, but H2O2 (just one more oxygen atom) is Hydrogen Peroxide, which is absolutely not drinkable.
One atom takes a world of difference.
Heavy water contains a different (heavier) isotope of hydrogen than normal. It has one extra neutron. Chemically, heavy water and normal water are identical. This is high school chemistry: all isotopes of the same element have exactly the same chemical properties. [We are talking about chemistry, not nuclear physics. Different isotopes definitely have different nuclear properties but that is irrelevant here.] More precisely, the equilibrium properties of heavy water are identical to light water.
However – and this is why heavy water is dangerous – all biological systems are out of equilibrium, meaning that the amount, nature and quantity of chemical reactions in your body are determined by their relative rates, not their eventual equilibrium proportions. Heavy water is heavy, so it reacts more slowly than light water. Since basically every biochemical reaction involves water, having a substantial amount of heavy water in your body alters all the rates of biochemical reactions (and not all equally), so it messes up the balance between different chemical processes.
This is strictly an effect of non-equilibrium dynamics which is extremely subtle. It’s not nuclear physics and it’s not equilibrium (normal) chemistry or thermodynamics either.
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