The point is to fill the space in a reactor without adding thousands of heat MOX reactors need to replace. The point of THAT is to make automation easier. I don't want fuel rods where they don't belong. I figured making a Plating with 0 effect values would be easier than a new part or part adaptation.
Call it "Full containment plating" with very significant explosion reduction and make it hard to build; call it "structural plating" and make it easy to build but little effect (-5% explosion size?); call it "Filler" and make it out of 2 iron plates and it does nothing.
My current reactor is an "efficiency" reactor, so it has 17 spaces to fill. Even with "containment reactor plating", I'll be adding 8500 heat even with the standard containment plating, almost double its normal. If I decided to make the significantly cheaper normal "reactor Plating", it will add 17000 heat capacity to the reactor.
Heating up a MOX reactor currently will take twice as long, if not more.