When I was looking up the recipe for the reactor casing and uses for the tough alloy it causes the client to crash.

Here is the crashlog.

The game crashed whilst rendering item
The game crashed whilst rendering item
Error: java.lang.ClassCastException: it.unimi.dsi.fastutil.ints.Int2ObjectOpenHashMap cannot be cast to gnu.trove.map.hash.TIntObjectHashMap

Which version of Forge are you using? The connected textures mod has an issue with later versions of Forge, and what I imagine is happening is that the game is crashing when showing the recipe from the transparent casing (which uses CTM).

I let them know about this a few days ago, so the devs are aware :)

This seems to have been fixed on CTM's side :)