my mark 1- 100eu/t infinite cycle reactor.

Um, that's 40EU/t ..

Depends how horriby inefficient you want to be, I guess.

Using the older ones, the closest it could have been would be 50eU/t and 2.5 eff (otherwise you run out of space)

Quote from Nargon

This contest is pointless. Mark-I reactor has a maximum 2.33 efficiency and that's made several times. For efficiency of 2.5 is required to place four of uranium in a row. For this it is necessary to internally cooling the 39 heat. It is not possible to deploy HT and coolant cells for cooling that much heat.

My best design with effeciency 2.5 is Mark II-E: http://test.vendaria.net/index…CCCHUCCHCCCCHCCCHCCCHCCCH
This produce only 3 heat.

Here is his design in the new reactor planner.
http://www.talonfiremage.pwp.b…=1k10101001501521s1r11r10

Here's are two new designs which compromises efficiency in numerous aspects to reach your goal:
http://www.talonfiremage.pwp.b…=1k10101001501521s1r11r10

http://www.talonfiremage.pwp.b…=1k10101001501521s1r11r10

You'd probably be better off building four of these; they each average ~28eU/t (including cooling time) and you can even run them to all pulse at the same time off of a single timer circuit.

http://www.talonfiremage.pwp.b…=1o10101001501521s1r11r10

HEAVILY recommend RP2 for making a time circuit the super-easy way (you'll need the last 1.8.1 compat. release; which is RP2pr3); but you (should be able to; untested) build one within a single chunk if you use multiple levels, a 1 second base clock, and a counter.