How did the Cold War cause Chernobyl? Or did it?
"It was a direct consequence of Cold War isolation and the resulting lack of any safety culture." Is this true?
That society was different
I will make the opposite argument. The Cold war as it happened from 1946 to 1988/9, had very little to do with Chernobyl. I would say that Cold War, no Cold War, it was the nature of the Soviet system for an incident like this to occur.
There are many examples of pollution with nuclear waste and accidents, plus reckless testing of nuclear weapons.
https://en.wikipedia.org/wiki/Lake_Karachay
The Soviet system was closed off by its own choice and it was paranoid of outsiders. Even in the interwar period of 1920s-1930s it was constantly looking for external and internal enemies (generated by external enemies).
In propaganda the USSR often showed itself as the lone red rock, the Communist lighthouse in the dark seas of capitalism. It would not have cooperated on nuclear safety anyway.
The USSR had a lot of bad institutions with a lot of bad incentives. Lying and fearing the Checka/NKVD/KGB was so normal that people rather lied about natural events and the laws of physics as opposite to tell the truth. If the tovarsih/comrade/elvtars told you that the Volga flowed backwards, it flawed backwards. Anything else was the result of "ideological undereducation."
Hungary has a good comedy movie about this, called "The Witness".
A random man from the countryside gets appointed as the director of an agricultural research institute. The job of the place is to grow oranges. He manages to grow one, lonely orange. Which gets eaten by a child so he has nothing to give to the General to taste. So he is given a lemon and he calls it an orange. Everyone just rolls with it. The Communist politician claims this defeated imperialism. This view comes from Hungary’s bitterness for being conquered multiple times in the 20th century and occupied by multiple powers.
This attitude can also be seen in agriculture:
https://en.wikipedia.org/wiki/Virgin_Lands_campaign
Mind you the USSR wasn't all stupid. It still was the world's second largest economy and according to people who lived in it, but hated the repressive system, it managed to provide high quality education and good quality universal health care.
So it wasn't that the USSR was run by idiots, but at the same time, the way they behaved wasn't normal or desirable.
Was this because of the ongoing "competition" between the USA and USSR, so they tested weapons recklessly without further caution?
The USSR always saw itself as competing against everyone else. So in the interwar period it targeted the British Empire and other European powers as the main enemy of the state of the USSR. (So it would try to create a condition of struggle against the neighbouring states that it did not control.)
While the state was insular, Stalin invited American industrialists to build infrastructure and import technology into the USSR. Of course as Lenin wrote it was quite cynical: "we will beat them with their own power, we will build up ourselves with their own money." which lead to the infamous phrase of "we will hang them with their own rope, that they sold to us."
Looking at the USSR in the interwar period and contrasting it with the Cold War period allows some good insights.
So the USSR always tried to produce propaganda that showed it was better than the neighbours or that it was better than the old Russian Empire. It was willing to damage the environment or pollute in order to achieve state goals.
In the book The Rise and Fall of Communism by Archie Brown, I noticed a point that I also picked up when reading Marx's essay. Communism is a materialist ideology, it is quite hostile towards spirituality or towards an ideas based theory of history, it only cares about material conditions.
This causes the Communist regimes to not care about the environment, until the damage was visible and started effecting the population.
So the USSR was quite a pollution heavy state as long as it enabled the output of manufacturing and raw materials that met that expected managerial plans.
So it didn't mind the pollution in the 1950s-60s.