how do I acquire plutonium? I don't see a way to crafting it. I am using this mod with it. https://mods.factorio.com/mod/RITEG

You get it by processing used up uranium fuel cells (and used up breeder cells).

Is that from a technology? if so which?

Nuclear fuel reprocessing

that has a recipe that gives me "Plutonium-239" 80% and "Highly enriched uranium" 20% but not "Plutonium"

I am trying to use this mod to burn up depleted uranium via this mod, https://mods.factorio.com/mod/RITEG. it has link-ins to this mod and one other mod.

this is an image of what I see when I unlock the tech in a testing world. https://photos.app.goo.gl/21nzFZUJGZ4Mv3x99

https://mods.factorio.com/mod/Nuclear%20Fuel/discussion/602a1eb445757e592fcc767e
https://mods.factorio.com/mod/PlutoniumEnergy/discussion/602a1d2aaeb4c6fd76f9377f
https://mods.factorio.com/mod/RITEG/discussion/602a24eb8f36cf57241a9410
link to all 3 threads of this story.

TLDR Schall Uranium Processing is having problems with Nuclear Fuel
I started testing mods these are my results.
1=active mod 0=inactive

Nuclear Fuel: 1
Plutonium Energy: 1
RITEG: 1
Schall Uranium Processing: 1
Result: crafting bugged

Nuclear Fuel: 0
Plutonium Energy: 1
RITEG: 1
Schall Uranium Processing: 1
Result: crafting working

Nuclear Fuel: 1
Plutonium Energy: 0
RITEG: 1
Schall Uranium Processing: 1
Result: crafting bugged

Nuclear Fuel: 1
Plutonium Energy: 0
RITEG: 1
Schall Uranium Processing: 0
Result: crafting bugged

Nuclear Fuel: 1
Plutonium Energy: 1
RITEG: 1
Schall Uranium Processing: 0
Result: crafting working

when Schall Uranium Processing and Nuclear Fuel are active mods RITEG's crafting and nuclear-related crafting don't work.