Can heavy water used in nuclear reactions be drunk? Those who have drunk it say it's sweet?

Reviewer: Gan Qiang

Lecturer at Beijing Institute of Technology, PhD in Applied Chemistry What is water? Since we learned chemistry in junior high school, we have firmly remembered that water is H2O, so this seems to be a really stupid question, but chemists don't think so.

Everyone knows that ice melts at 0℃, but do you believe that there is a kind of ice that can only melt at 3.8℃? It does not require any special pressure or other environmental conditions, nor is it mixed with any other substances. It is just pure, authentic water, but there is something different. It is called heavy water .

The left side is heavy water ice, and the right side is ordinary ice

What makes heavy water heavy?

Simply put, heavy water is just denser than ordinary water (which we call "light water"). Microscopically, both ordinary water molecules and heavy water molecules are composed of 2 hydrogen atoms and 1 oxygen atom. The difference is that the chemical symbol of hydrogen atoms in ordinary water is H, which is called "hydrogen" (or "protium"), while the chemical symbol of hydrogen atoms in heavy water is D, which is called "deuterium" (or "deuterium"). What is the difference between H and D? In fact, the nucleus of ordinary hydrogen atom H contains only 1 proton, while the nucleus of heavy hydrogen atom D has one more neutron, so 1mL of light water at 20℃ is 0.9982 grams, while heavy water is 1.056 grams. In addition, the third type of hydrogen atom is T, called "supertritium" (or "tritium"), which also has 2 more neutrons in the nucleus.

From the appearance, there is no difference between heavy water and ordinary water. Both are colorless and odorless liquids. And because they are substances composed of the same elements, their chemical properties are very similar. But if you say that there is no difference at all, no one will believe it.

In nature, the distribution of heavy water is very uneven. The content of heavy water in snow, rainwater and surface water is very small. There are about 7.5 kilograms of heavy water in every 50 tons of ordinary water. Therefore, in order to obtain heavy water, people generally use the method of electrolyzing ordinary water. Since heavy water cannot be electrolyzed, the concentration of heavy water in the electrolyte will become higher and higher, and finally purer heavy water will be obtained. However, the heavy water prepared in this way will consume a lot of electricity. The electricity required to refine 1 kilogram of heavy water is 3 times more than that required to smelt 1 ton of aluminum.

So why do people continue to electrolyze water to produce heavy water? This is because in modern nuclear reactors, heavy water participates in chemical reactions more slowly than light water, and is by far the best neutron moderator . It plays an important role in the process of making nuclear fuel, and heavy water is less likely to absorb neutrons, which may make the chain reaction sustainable.

Is heavy water poisonous?

When heavy water first came into people's consciousness, it was associated with nuclear reactors. Although we now know that it is not very dangerous, many people's first impression of it back then was that it was extremely dangerous.

However, scientists' curiosity is endless, and someone drank heavy water shortly after it was discovered.

This man is George Charles de Hevesy. His name may be unfamiliar to most people, but if you have heard of the story of dissolving the Nobel Prize medal with aqua regia, you can also get a glimpse of this scientist's character from it. But that is another story and has nothing to do with heavy water today. Let's get back to the point. When it comes to drinking heavy water, we first consider its toxicity.

Although heavy water is not radioactive and is not a toxic substance, living things only need ordinary water. This is just like the nitrogen in the air is non-toxic, but inhaling high concentrations of nitrogen will cause suffocation due to lack of oxygen. If you only drink heavy water, your body functions will definitely be affected.

In mouse experiments, it has been found that heavy water can inhibit cell division (the lethal concentration of heavy water is 60%), causing tissues that require rapid metabolism to die due to large-scale cell death, such as hair roots or gastric mucosa, which will be the first to have problems. The good news may be that the growth of cancer cells that originally grew rapidly will also slow down, but the degree of slowdown is not very helpful for cancer treatment.

Plants will gradually wither in a heavy water environment with a high concentration.

Source | Paper "The biophysical effects of deuterium oxide on biomolecules and living cells through open notebook science"

What is clear is that heavy water currently purchased through formal channels will basically have safety warnings or reminders such as "for experimental use only" on the bottle label. It is not recommended for anyone to try drinking heavy water.

Is heavy water sweet?

But theory is theory, and drinking a little bit is not a big problem, so countless people have tried the taste of heavy water. As for the reason why so many people "follow the trend" and try heavy water, it is a bit strange - is heavy water sweet?

Source | Excerpt from Popular Science report

Why does water taste sweet? According to the plan of a curious foreign blogger, he convened and set up a simple blind test experiment, in which the subjects tasted different types of water in turn, three drops each time. In order to eliminate irrelevant factors, such as sensory differences caused by weight, he also spent a lot of money to buy heavy oxygen water (also known as oxygen 18 water) with the same molecular weight as heavy water. As a result, almost all the subjects were able to distinguish heavy water, and the identification speed was very fast.

Source: Thunderf00t

In another taste test experiment, 22 out of 28 participants were able to accurately distinguish heavy water. According to the participants' feedback, the sweetness of pure heavy water was the most obvious, but the overall taste was light, with an average sweetness of 3.3±0.4.

Sweetness perception (1 no sweetness, 3 slight sweetness, 5 medium sweetness, 7 very sweetness, 9 very sweetness)

In order to further study the reason why heavy water produces sweetness, the second experimental team also conducted experiments on mice. The results showed that mice had a strong preference for sucrose water, but had no sensitivity to heavy water. Mice were even observed to show aversion to heavy water.

Source | Paper: A Study of Taste and Smell of Heavy Water (99.8%) in Rats

This leads to a speculation: the reason why heavy water tastes sweet may come from sweet taste receptors that are unique to humans but not in rodents.

Source | Carmelo Tempra / IOCB Prague

Further experiments confirmed that the TAS1R2/TAS1R3 receptors are the ultimate reason why humans can taste the sweetness of heavy water, and subsequent receptor inhibitor experiments also proved this in reverse. However, the exact location and mechanism of action have not yet been found, and further research and discovery are needed.

In short, here is a useless piece of knowledge: when there are two glasses of water in front of you, you can tell which one is heavy water by taking a sip, but cherish your life and please stay away from heavy water!