Going around the satellite map of Siberia is a kind of pilgrimage where you are very tensely looking at stripes on the soil, trying to not confuse natural geological valleys with the actual remains of extermination camps. Retchlags : rezkhoïe fizitcheskoïe istochtchenye laguereï, camps of death by exhaustion through forced work. My estimate is of 27 million victims for the period 1943 (with an early start in 1939 in Novaia Zemlia) to ~1985/87… an old estimate still written in 2018 articles is of 20 millions but I found this not enough. And the 27 million does not include, still, the Eastern Block since I am relying on a retro-analysis of Soviet statistics. People were, mostly, directly forced to work with peaks on corridor uranium mines, to fill them up with uranium so that their dead bodies (after a few weeks) can be directly severed up and the parts most heavily filled with uranium (feet, legs, hands…) directly cycled into plutonium production in RBMKs (the flesh serves as neutron moderator). Birkenau in Nazi Germany started the trend with uranium showers in the chambers (“Zyklon B”) and crematory ovens were subcritical nuclear reactors (for the antitank rockets). The Soviet Union frequently used sodium fast neutron reactors (from the 1970s…), and (in the early times, after their discovery of Birkenau and before mastering well fast neutron reactors) an “intermediate” between Birkenau and the fast neutron reactors i.e. reactor cores set in holes in hills, because Retchlags were in nature flying extermination camps, since Siberia has so much uranium, and putting the body parts overloaded with natural uranium in a core and bringing a press to compress from above is enough.
In the book by Avraham Shifrin (copy of his chapter on extermination at the end of this) the Achinsk case corresponds fully to the picture above and to the other one below. Shifrin says this area is an open-pit uranium mining area and uranium enrichment facility.
More cases where my answer is definitive in spite of the apparent uneasiness :
Finding the areas, not confusing with valleys, is a difficult work and I am maybe leaving many retchlags because of my tendency to discard when I do not have full certainty.
See also the case of the “Golden Hill” which clearly is a case of a primitive plutogenic core with human remains from Cheliabinsk :
So this prime case of human body nuclear accident happened, likely, in the mid 1960s. “Golden Hill” was the name of the area when archeologists went there in 1990, certainly because of the nuclear flash the day of the accident. At least Birkenau ovens were subcritical…