I think the biggest point of Chernobyl is the setup that actually caused the accident. Set that up, and you'll have a way more interesting campaign than a stock post-disaster game.
The key issues that caused Chernobyl:
- National culture of communal success, but individual failures. This was shown in that no one could believe that the RBMK reactor could explode, so it must be an operator error
- A government that relies on heavy secrecy, so people would have no idea that there's even a problem. This was evident in that they knew that the RBMK reactor had flaws, but didn't tell anyone. Hell, they even had a minor incident 4 years earlier and didn't tell anyone. It took Legasov's suicide two years later for the Soviet scientific community to do anything
- Institutional corruption and incompetence. They wanted to get that safety test just for the leaders to get a promotion, regardless of the results. It was supposed to be run at 50% power, but was far below that, ruining the goal of the test
How do we translate that to fantasy?
Well, having some sort of wizard's college that knew whatever magical technique could go wrong would be the easiest. Their ego in not stating that their new process was flawed is pretty understandable. The hard part is to make a nation that is structured, bureaucratic, and secretive. Aspects not usually seen in medieval fantasy.
I think if you focus on mimicking the steps to Chernobyl, the results of the incident become far more interesting. How much would your players learn? What if they learn too much?
