Mislinked? I see a Mark V with 3m 44s of runtime before explosion.
My Mrk. I-O-SUC 2.75 Effciency Reactor Desgn
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And here's a 3 efficiency Mark 1-1-SUC in a single chamber setup.
Similar: one less uranium cell, 10 more EU/t (eff 3.44 instead of 3.0).
Or: still nine uranium cells, 30 more EU/t, but requires some coolant cells (eff 3.67).