April 26 1986 Chernobyl Nuclear Power Planet.
The day shift arrives to take over from the evening shift. Many of the workers want to know if the safety experiment, using residual energy from the steam turbine to power water pumps until the emergency generators could kick in, was a success, and therefore they would get their bonus, or if they would have to do it.
There is confusion at the planet and the workers are told to wait. Some of they suspect the worst and check their radiation dosimeters but are relived to find that the radiation level is the normal background. Nervous officials from the power planet can be seen hurrying about. It becomes obvious that something has happened but everybody is tight lipped about what has transpired.
Eventually the day shift are sent home with an injunction not to talk about what they've seen. Rumours abound that a specialist nuclear engineering team is flown in from Moscow to deal with what ever went wrong with Reactor number 4. Other darker, rumours proliferate at that speed of light, telling tales of the runaway reactions, of fires, partial meltdowns and people killed and injured. Workers from the planet whisper that this isn't the first time that such an incident has taken place at the complex and they mutter about reactor number 1.
The Soviet nuclear oversight regulator announces that Reactor Number 4 at the Chernobyl Nuclear Power planet with be shutdown for maintenance. No time frame for the maintenance or an expected completion date is given. It will turn out to be years and will be an almost total overhaul of the reactor. At the same time a report is commissioned into the design and operation of the RBMK 1000 reactor. This report will eventually recommend a number of changes to the reactor design. These changes will be reflected in the two new reactors at the Chernobyl nuclear planet; 5 and 6.
The senior staff who where operating the planet on the morning of the 26th are charged, thought with what remains secret, and are hustled out of their roles.
Leaks and rumours find their way to the West but these are vague merely stating that something happened at a nuclear power planet. Which nuclear power planet it is changes with the teller, Leningrad, Kursk, Kalinin, Smolensk and some obscure place, Chernobyl. Western intelligence agencies know something happened at the planet but most of their resources in the area are focused on the "Steelyard" aka "Chernobyl 2" or "Durga-3" an over the horizon radar that is part of the ABM early warning system.
Okay. In this timeline there was an accident at Reactor number 4 but with more luck then anybody has right to there wasn't an explosion. The reactor is trashed but still intact. So what are the effects? The Soviets are redesigning the RBMK-1000 to eliminate most of the design flaws that lead to the explosion in OTL, so there won't be another reactor disaster. A number of RBMK-1000 reactors that where planned for but not built subsequently due to the disaster, some of those would still be built.
Chernobyl is often cited as the turning point for Glasnost. If there wasn't a disaster or there was one that could be covered up, like the earlier partial meltdown of Reactor #1, would Glasnost have been seen as window dressing? Would hardliner shift against the policy? Would the fall of the Soviet Union be delayed?
Without Chernobyl would Nuclear power be more common in the West? Or would Three Mile Island be enough to delay it?