Reactor Design Principles

You can design your reactors as you wish. In general, dual or quad rods are more fuel-usage efficient (e.g. they generate more total RF per pellet), but are also much harder to cool.

You can use active cooling with the heat absorbers, or passive cooling with just heat vents. When surrounded by active components on all sides, a single absorber may absorb up to 16 * 4 = 64 Heat per Tick, but does require ice to work. You can create ice from water with the industrial chiller.

A single heat vent can vent heat based on the hottest neighboring block. At 1000 Degrees, it will vent 14 Heat, and at 0 Degrees just 4. Depending on your goals you probably want to either spread the heat with heat spreaders to many vents, or surround a few absorbers with heat pipes.

Based on the provided formulas, here's a small table that did some of the math for you:

Rod Type	Rod Count	Internal Pulses	External Pulses	Total Pulses	Heat Generated	RF Generated	Vents needed at 0 C	Vents Needed at 1000 C	Absorber Contacts needed
single rod	1	1	0	1	4	32	1	1	1
	1	1	1	2	6	64	2	1	1
	1	1	2	3	8	96	2	1	1
	1	1	4	5	16	160	4	2	1
double rod	2	4	0	4	12	128	3	1	1
	2	4	1	5	16	160	4	2	1
	2	4	2	6	22	192	6	2	2
	2	4	4	8	36	256	9	3	3
	2	4	8	12	76	384	19	6	5
quad rod	4	12	0	12	76	384	19	6	5
	4	12	1	13	88	416	22	7	6
	4	12	2	14	102	448	26	8	7
	4	12	4	16	132	512	33	10	9
	4	12	8	20	204	640	51	15	13
	4	12	16	28	396	896	99	29	25

Reactor design can vary. A small reactor may be good enough for early-midgame power generation, while massive reactors may be needed in the lategame. When testing designs, it is often advisable to use small pellets to allow faster shutdown should the reactor begin overheating.

Usually a few fuel rods are surround by heat pipes and cooling components, as below:

For bigger reactors with denser rods, you'll need a lot more cooling. Note that not all interior blocks need to be filled: