"Environmentalists" is a large, diverse group and nuclear energy has been a controversial topic splitting the group for decades.

Many environmentalists are pro-nuclear, and viewed exclusively through an environmental lens, nuclear is likely the best energy source.

Other people share the "environmentalist" label because they care about clean air, unpolluted rivers, biodiversity, climate change, etc but they oppose nuclear on unrelated grounds (eg, as part of an anti nuclear weapon proliferation agenda) or out of fear of adverse events from damage to an energy facility.

The "pro-environment but anti-nuclear" subgroup held power within the Democrat party in the US through most of the cold war era. The "pro-environment, pro-nuclear" subgroup is now the largest group within the Democrat voting base, but some of the people and all of the regulations from the 1960s-1990s are still in power.

Good reply; factual. But in case you are not aware, “Democrat party” is a bit of a slur [1]

[1] https://en.wikipedia.org/wiki/Democrat_Party_(epithet)