One nuclear weapon test in the atmosphere releases more radiation into the atmosphere than all the nuclear reactors that have ever existed put together. And many more nuclear tests have occurred than there have ever been nuclear plants in existence, since the first one was constructed in Chicago in the 1940s.

Our rising atmospheric temperatures are perfectly explained by greenhouse gases, that is, the earth is getting hotter because the heat from the SUN is trapped here by CO2 in the air. The heat generated by burning fossil fuels is insignificant compared to the solar heat that is trapped here by the greenhouse effect.
And the heat generated by nuclear radiation from reactors is insignificant to that generated by the steam plants themselves in the process of creating electricity.

Although I doubt that man-made radiation has any role in climate change; if it does, then certainly the radiation releases from weapons testing far exceeds that from nuclear power plants--by many orders of magnitude.

In the upper right corner of the home page of this website:

https://neven1.typepad.com/

is a little graphic that documents the amount of heat that is accumulating in the atmosphere from the solar greenhouse effect, displayed in units of Hiroshima bombs. The counter is continuously running, and should demonstrate that this greenhouse heat accumulation completely dwarfs the contribution from bombs, which in turn completely dwarfs the contribution from reactors.

Human fission technology simply CANNOT create enough heat energy to make a difference to our climate.
It is truly insignificant. However, human combustion technology CAN affect the ability of the atmosphere to trap solar heat. And although this additional solar heating is only a tiny part of the earth's energy budget, the weather/climate system is extremely sensitive and can react to it. A rise of only a degree or two can easily alter the climate in measurable ways. That's why its called the Greenhouse Effect. Its a lot more effective to keep your orchids warm in winter by putting them in a greenhouse than it is to light a candle for heat.

Banning nukes is not going to stop global warming. In fact, it will probably make it worse--although for totally different reasons.