Was playing around with a MOX design that I could easily spam with 0 chambers and I ended up with this. I think it's nicely space efficient.
Code: 0C0A0C0000000000000A050A0000000000000A050A0000000000000C0A0C0000000000000A140A0000000000000A050A000000000000
EU/t: 352
Efficiency: 11.7
Obviously not as fuel efficient as some but it's pretty easy to spam as you're trying to increase your plutonium stockpiles.