Co-60 by default lasts about 5 weeks in a reactor, which is quite a long time. With moderation (either by moderator rods or by running it in water based coolant) this gets quartered to ~9 days. When running the reactor supercritical and going over the neutron maximum (256 neutrons, so quite easy) we get this quartered again, one rod now lasting ~2 days. Now, since durability loss now scales linearly with power output, lets go over the neutron maximum several times. If we for example have a neutron count of on average 5000 on the rod, that means we will lose durability 5000 / 256 = ~19.5 times faster, the rod now lasting ~2.7 hours.
That is quite fast but still not amazingly fast and requires automation to be useful. And then that would only yield you some Thorium, which can’t go critical without the 1x1 reactor and then would take the same amount of time to burn (2 times the durability but half the maximum) and still only yields U-238.
It is probably best to look at the real use-cases of a burner reactor:
- U-238 to U-235: Burning U-238 would take 2 times longer than Co-60, because at the same default duration, the maximum is twice as high as Co-60. That means ~5.3 hours. To get a full rod of U-235 we need to burn 9 U-238 rods, taking exactly 2 days.
- U-235 to Pu-244 to Pu-241: We want Pu-241 because of the lower factor making it much better, while Pu-244 is more or less equal U-235 from a stat perspective. So U-235 lasts 5 times less but has a 4 times higher maximum than U-238, making burning one rod at 5000 Neutrons take 2.5 days. Burning Pu-244 takes the same amount of time because of the sharing in relevant stats with U-235, making burning U-235 into take 25 days total (since you need 9 Pu-244 rods).
- U-233 to Pu-243: U-233 lasts 5 times longer than U-238, meaning burning it into a rod of Pu-243 takes 12.5 days. Since you already must have a breeder reactor at this point, it is probably better to try squeezing out some Pu-239 with it.
- Getting Enriched Naquadah or Naquadria: There is probably little reason to even attempt this, your best starting point would always be Pu-239, taking 10 days to get one rod of Am-241, taking 90 days to get the 9 rods needed for one rod of Enriched Naquadah, taking an additional 10 days to burn that to Enriched Naquadah (100 days total for it at 5000 Neutrons on the burning rod). To burn Enriched Naquadah you need even more than 5000 neutrons to even cross the maximum, but I will continue the calculation with 5000 and pretend it crosses the maximum, making it more easy to calculate the time it would take with more realistic neutron counts. So, 900 days to get the Enriched Naquadah needed and then just an additional 100 days to burn it into Naquadria. Gives you a nice round 1000 days to burn your way from 729 rods of Pu-239 to 1 rod of Naquadria. Even if you do something absurd like 10 times more neutrons on the rods, meaning 10 times quicker burning, it would still take 100 days real time, having to deal with the heat of 50000 neutrons, so more than 3 large heat exchangers required.
So, after carefully reviewing this data, I’ve come to the conclusion, that you’re kinda right. I’ll dial back the return from 4/72 of a dust per rod to 6/72 of a dust per rod. I’ll also make water based reactors (heavy and tritiated water to be exact) more useful as burner reactors by making them lower the neutron maximum of the fuel rods quite significantly. Exact numbers undecided, but something like an at least 8 and 16 times lower neutron maximum. This should give burner reactors a more useful niche.
My solution to somewhat remedy this would be to disable getting 235 from centrifuging, having to go to the uranium-fluorite processing chain instead (or burner reactors). U235 is really your gateway into breeding and therefore getting better fuels, even one rod of it being enough to make you never need to get any more of it.
To make Thorium more available, maybe a way could be to make Co-60 much less useful for power production but more easily burnable. A lot of people seem to be running Co-60 because it is super abundant and better than Thorium for power production because it can go supercritical, so it would smash two flies at once. Thorium is not really meant to be used directly as reactor fuel, but for either breeding U-233 or for Molten Thorium Salt Reactors, so it being less abundant is not really that much of an issue imo. What could be an issue is that breeding U-238 into Pu-239 is too easy compared to breeding Thorium into U-233, so U-233 breeding would become redundant, but that remains to be seen.
Configurable duration is also something that might be worth looking into, but it also messes with the balance of burner reactors, so it would maybe be better to just change the current values and rebalance for that instead.