The Half Life of Valery K by Natasha Pulley

Loosely based on true events at a Russian nuclear facility in the 1960s, The Half Life of Valery K (2022) follows the story of a Russian nuclear scientist, pulled from a freezing gulag to lend his expertise to what seem to be human radiation trials at the mysterious City 40. Never sure who to trust and who to fear, he picks his way through a minefield of misinformation and mystery. 
Natasha Pulley adds her trademark slow burn, queer romance with delightfully awkward and surprisingly tender characters. It's a treat to read her historical fiction with a touch of whimsy and morally ambiguous heroes. 
For readers of TJ Klune and Kate Quinn.