https://www.bbc.com/news/world-60664169
This is a general article from last September...
it lays it out fairly well.
As for size and location ... I would say
yet to be determined
The real question is ....
How would the world react ?
Would you push “the button”?
From your link:
“However, Russia might also be deterred from using tactical nuclear weapons by another power - China.
“Russia is heavily dependent on Chinese support,” says Dr Heather Williams, nuclear expert at Kings College London.
“But China has a ‘no first use’ nuclear doctrine. So if Putin did use them, it would be incredibly difficult for China to stand by him.
“If he used them, he would probably lose China.””
—Would you push “the button”?
I make no claim to strategic thinking, that said, other than a pure terror weapon there would be little to gain for Russia.
A ‘dirty’ event in Moscow would do far more damage. Not explosive, simply a car with radioactive exhaust driving around the city. Or a radioactive saltshaker... Or two or three...