[pcm81]

The story is being covered on MSNBC and perhaps other networks. There was an explosion at a missile testing site in Russia last Thursday. The actual Russian news agency was reporting that evacuations to be under way because of the danger from "isotopes" used in fuel. Word "isotopes" was specifically used in the Russian reporting. The conspiracy theories are now building about a nuclear powered missile that Russians may have been testing. There are no official confirmations that the said missile was powered by nuclear reactions, rather than traditional chemical fuel. The use of the word: "isotopes" in official Russian reporting seems suspicious. Tell me if i am wrong, but as far as i know there are no chemical reactions that care about isotope composition] of elements involved.

My specific question is whether there are chemical reactions, however exotic they may be, that would care about isotope composition of elements involved.

[Enthalpy]

For hydrogen, the isotope makes a useable difference. The influence is even smaller for lithium, but is used too
https://en.wikipedia.org/wiki/Lithium#Isotopes
https://en.wikipedia.org/wiki/Isotopes_of_lithium#Isotope_separation
https://en.wikipedia.org/wiki/COLEX_process

The difference between deuterium and protium is big enough that the standard process to isolate deuterium bases on chemical separation.

The source of deuterium is water. While physical processes like gaseous diffusion would separate D₂ from ¹H₂ quickly, they require to reduce the hydrogen first, which consumes much energy. The answer is to begin by enriching chemically the water in HDO, and reduce the hydrogen only then.
https://en.wikipedia.org/wiki/Girdler_sulfide_process

[pcm81]

For hydrogen, the isotope makes a useable difference. The influence is even smaller for lithium, but is used too
https://en.wikipedia.org/wiki/Lithium#Isotopes
https://en.wikipedia.org/wiki/Isotopes_of_lithium#Isotope_separation
https://en.wikipedia.org/wiki/COLEX_process

The difference between deuterium and protium is big enough that the standard process to isolate deuterium bases on chemical separation.

The source of deuterium is water. While physical processes like gaseous diffusion would separate D₂ from ¹H₂ quickly, they require to reduce the hydrogen first, which consumes much energy. The answer is to begin by enriching chemically the water in HDO, and reduce the hydrogen only then.
https://en.wikipedia.org/wiki/Girdler_sulfide_process

Thanks.
It's good to know that there are some chemical reactions that are sensitive to isotope composition. However it sounds like these are reactions that consume energy to produce isotope isolation. Point being is: for exothermic reactions that are usable as propellant the isotope composition would be unimportant.

[Enthalpy]

That's my opinion too.

These projects are secret, the Russian developers and politicians misinformed the other countries about them just like Nato does with wrong goals, designs, figures, and mixing up project natures and names.

The people who described the accident to the Press lied as part of their duty and they probably understood little about technology. The reporters understand zilch usually, mix up the information, and put anything in their paper. "Experts" and "senior analysts" just say anything random.

What elements of information are credible in this context? Maybe the explosion, the deaths and injuries, the small spike in radioactivity, very little more. Good luck to infer anything from that.

Source related with the project spoke of "liquid propulsion" and "isotope power source" if the translation is accurate. In Western media it became "missile" and "nuclear reactor", even "Burevestnik".

I strongly doubt the tested thingy was a missile.

[gippgig]

It has nothing to do with this incident, or with the chemistry involved, but isotopic composition would make a difference since propellant weight is important. For example, removing the 1% ¹³C from kerosene should increase performance by roughly .07% simply because it would weigh less (only ~.03% for a rocket where the oxidizer is carried on board), seldom worth the cost. Boranes have been investigated as fuel; using ¹⁰B instead of natural B should increase performance by ~7% (for B₅H₉ in an air-breathing engine).

[Enthalpy]

[...] seldom worth the cost.[...]

Yes.

Boranes are no-no at rockets and I suppose missiles. They were indeed investigated in the very early times, among many unreasonable proposals. I guess nobody considered them seriously even at that time, but money was available. Acetylene (boom) had been investigated too for instance, and acetylene dinitrile, tetranitromethane, fluorine, NF₃, OF₂, plus many more.

Presently, not only are hydrazines and N₂O₄ being phased out. Things like hydrogen peroxide (ignites about all organics by contact, then detonates) and even nitromethane (can be brought to detonate) are unwanted.