Note: I'm not a native speaker, so my English could be incorrect

Pack Version:
Nomifactory 1.2.2.1

Description:
You can make 1 Uranium 238 Dust and 1 Tiny Clump of Uranium-235 from 1 Uranium 238 Dust, so Uranium-235 can be duplicated

Expected Behavior:
Uranium-235 shouln't be able to be duplicated

Steps To Reproduce:

1. Throw an Uranium 238 Dust into Thermal Centrifuge to get an Uranium-238 and a Tiny Clump of Uranium-235.
2. Make 144 mB of Uranium 238 fluid from an Uranium-238 with Fluid Extractor.
3. Solidify 144 mB of Uranium 238 fluid with Fluid Solidifier to obtain an Uranium 238 Ingot.
4. Pulverize an Uranium 238 Ingot to obtain an Uranium 238 Dust.
5. You can use this Uranium 238 Dust to start from step 1 again. Also, you'll get an extra Tiny Clump of Uranium-235.

Screenshots:
Step 1:

Step 2:

Step 3:

Step 4:

This issue was fixed in 1.3 development snapshots in August 2020: 240fe8f.

1.2.2.1 is several years behind current updates; it is derived from our 1.2.2 release from April 2020. For an up to date experience please play on the latest 1.3-RC version from CurseForge.