I just want a way to use up my extra bits of Uranium 238 and MOX fuel looks like it could be a faster way to make more Plutonium since they run for half the time.
MOX is actually super safe to work with. Or at least, doesn't have to be dangerous at all.
First, MOX CAN be used in the place of uranium fuel rods in a regular reactor. In that sense it works exactly the same. HOWEVER, as it generates more power the hotter the reactor is, it does open up the possibility of different reactor designs.
The simplest, and safest way to do this, is to note that the various cooling components in a reactor cool different things. There are components that can accept heat from adjacent rods, components that can accept heat from the reactors "hull", components that shed heat etc. About half the uranium designs accept heat from the rods, and shed it directly, the other half allow uranium rods to pump their heat into the reactors hull, and then the components cool the hull and the third half are a hybrid approach.
Now, to make a "safe" MOX reactor, we want a HOT hull, because heat gives us the EU multiplier. But we don't want to pump more heat into the hull - because thats hard to manage. So, the simplest thing to do is to create a reactor, put some fuel rods in it, turn it on, and watch. You have at least a minute before the heat builds to 10,000 (the explosion point), so you have ample time to let the heat build to 7,500 about, and then turn the reactor off and remove the fuel rods.
Now, if you leave the reactor alone the hull will not cool. It will stay indefinitely at that exact temperature. If you place any vents in it that take heat from the hull, then it will start to cool. Don't do that (unless you overheated it slightly and its setting fire to things around itself).
Here are 3 relatively high efficienty reactor designs, and the EU output is listed relative to 75% max heat - none of the components used in these reactors will cause the hull to cool, and all the fuel rod heat is diretly vented so the reactors are completely safe to run. Do note that any reactor plating components in the design are there to fill empty space to allow the reactor to be automated - they are not necessary to the design if you are manually filling it, and do have the unwanted side effect of increasing the max hull temp so it makes the reactor slightly more interesting to pre-heat.
0C0A0C0A0C0A0C0A0C0A141414061414140A0C0A0C0A050A0C0A0C0A0C0A1406140A0C0A141414140C141414140A0C0A0C0A0C0A0C0A
800EU/t @16x (2Quad 1 dual)
090C090C0C090C09001409140A0A14091400090C0A05050A0C0900090C0A05050A0C09001409140A0A14091400090C090C0C090C0900
640EU/t @16x (4 dual)
0A140A140A140A140A060A0C0A0C0A0C0A060A140A140A0C0A140A0C0A0C0A060A0C0A0C0A140A140A140A140A060A0C0A0C0A0C0A06
1200EU/t @12x (5 quad)
https://github.com/MauveCloud/Ic2ExpReactorPlanner/releases can be used to view the designs.
Nonetheless: if you still feel unsure and/or just want some style points: If you spray CF Spray on Iron Scaffold the CF will dry to Reinforced Stone; an IC2 material that has a blast resistance equal or higher than obsidian, and can be used - along with reinforced doors and glass - to make a "safe" chamber in which to experiment with unsafe reactor designs. Any actual explosions (coff) will propagate directionally through cabling holes so make sure cables leave the chamber from the roof or some direction that faces away from your base, or a clever S bend etc.