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This might be a stupid question, I'm not an engineer, and not really sure where to begin to research this. I tried Google but of course it's all biased toward news articles about Japan.

So let's start with what I know. Nuclear wastewater has tritium and other radioactive isotopes. Regular salt water can be boiled off leaving salt behind. Why can't we boil the wastewater off to leave behind the isotopes? I know they're atomic scale, so it's not quite the same but are there any publications where it has been tried and the results were documented?

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  • $\begingroup$ For motivation, here is why you don't want weird hydrogen isotopes in the environment. Life on earth that uses the Krebs cycle for ATP production really hates heavy hydrogen. Warning - it's a deep dive into biochemistry - youtube.com/watch?v=6P8gqB4zLGQ $\endgroup$
    – Phil Sweet
    Commented Jul 9, 2023 at 23:48

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To use your example, salt can be removed from water by boiling the water and condensing the resultant steam. This produces two products, distilled water and a dry salt.

The reason why this is possible is because salt is dissolved in water. Simplifying things, lets only consider common table salt, sodium chloride (NaCl). This applies to all salt. When sodium chloride dissolves in water it does not chemically react with water (H2O) to form hydrogen chloride, HCl, which is hydrochloric acid, or oxidized sodium (NaO). The salt stays in solution and when water is removed salt remains.

You mention tritium, which is one of the isotopes of hydrogen. What defines an element (hydrogen, oxygen, carbon, iron, etc.) is the number of protons in its nucleus. Hydrogen has one proton, carbon has six protons, oxygen has eight.

The other particle that an atomic nucleus can contain is a neutron. Protons have positive charge, neutrons have no electrical charge. Electrons have negative electrical charge, they orbit the nucleus.

Commonly, the nucleus of a hydrogen atom only contains one proton. However, sometimes it can contain one or two neutrons. This makes such atoms of hydrogen heavier than a typical atom with only one proton. A hydrogen atom with one proton is called deuterium and one with two protons is called tritium. When such atoms combine with oxygen to produce a water molecule the atoms are locked together.

Boiling such water only produces steam. If you want to separate deuterium and tritium from water, the water molecule must be split to produce hydrogen gas and oxygen gas. This can be done using electrolysis, where an electric current is passed through water.

Regarding the other radioactive wastes in the water, such a strontium and cesium etc. These elements can be removed from the water as you suggest, by boiling the water. This produces another problem, what to do with the radioactive power that remains when the water has been removed? How much energy must be used to do this and what does it cost? What form of energy will be used to do this: nuclear, renewables, coal, gas, solar evaporation? How much radioactive power would be produced and how is it then collected for "disposal" and how and where is it then disposed of?

Dumping radioactive water into the ocean is cheap and rids the utility of a inconvenient water storage problem. It gives the utility an opportunity to "move on" after so many long tortuous and expensive years.

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  • $\begingroup$ Thank you. To make sure I understand, I'd like to break it down further. With NaCl, it's not combining with the water atomically so it results in the chemical formula Na(aq)+Cl(aq), but with the hydrogen isotopes Deuterium and Tritium, the water picks up an extra proton (or two) on the hydrogen atom, resulting in something like 2H2O for Deuterium. This is also known as heavy water, right? So when you boil it, the Hydrogen atoms aren't losing the extra proton. Is that right? But if you perform electrolysis, it can split the proton off of the hydrogen atom again. $\endgroup$
    – Speeddymon
    Commented Jul 11, 2023 at 0:43
  • $\begingroup$ "... known as heavy water", yes. Also yes regarding hydrogen retaining the extra neutron during boiling. If hydrogen gained a proton it would become helium. Electrolysis would not result in hydrogen losing a neutron. Electrolysis splits the water molecule. $\endgroup$
    – Fred
    Commented Jul 11, 2023 at 1:39
  • $\begingroup$ I believe @Fred in his answer has confused deuterium with Helium. Deuterium is hydrogen with one proton, one neutron, and one electron. I am sure he knows it and will correct his answer. Same as it is for tritium, one proton, 2 neutrons, and one electron. $\endgroup$
    – kamran
    Commented Jul 11, 2023 at 3:13
  • $\begingroup$ @kamran: No confusion on my part. My answer does not mention helium. My reply to the comment is correcting an error made my by the OP who stated "Hydrogen atoms aren't losing the extra proton". If hydrogen had an extra proton it would be helium, not hydrogen. It's why my reply has neutron in bold & proton in italics. The OP should have written Hydrogen atoms aren't losing the extra neutron. $\endgroup$
    – Fred
    Commented Jul 11, 2023 at 5:48
  • $\begingroup$ "... Electrolysis splits the water molecule", into hydrogen gas and oxygen gas? So this hydrogen gas would still have the extra neutron (or two) and still be Deuterium or Tritium? So it would take a fission reaction (which as far as I understand, we haven't yet developed, or at least haven't yet controlled at scale) to split the neutron(s) off from that hydrogen. Thanks again for helping me "get" this. I hope one day we can find a way to not dump radioactive water into any ecosystem. $\endgroup$
    – Speeddymon
    Commented Jul 12, 2023 at 0:21

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