It only crashes on client startup, not server side.

crash-2018-06-02_17.44.15-client.txt

Any luck with this build?

Forge 12.18.3.2511. It's all in the details, in the crash log.
I'll try with the recommended 12.18.3.2185 and let you know.

Don't worry, I was using that version too.

Does the mod run fine on its own? Just wondering if there's a particular nasty mod-mod interaction happening.

I think I identified Not Enough Items as the faulty mod, but another mod must be in conflict, as when I run NuclearCraft alone with NEI and it's dependencies (JEI, CodeChicken Core and codeChicken Lib), it doesn't crash.

Edit : I added Mekanism and it crashed.

crash-2018-06-03_16.26.39-client.txt

NuclearCraft with only Mekanism don't crash.

Aha - found the fix. Thanks for the help - will get it out shortly :)

You're welcome :)

Here we are - on CurseForge now :)

Still crashing.
crash-2018-06-02_22.17.09-client.txt

Weird... I can't recreate this error, neither client nor server. Which version of Forge are you using?