also, uranium’s half life is 700 million years, so we expect (207/235)*7.5 (of lead) + 7.5 (uranium) ~ 14.106382978723405 lump.
also, a lot of the helium produced will remain trapped inside (most heavy metal lumps act as sponges for little gasses). but 700 mil years is also a large amount of time, so much of it would diffuse out. I could checkup diffusion statistics for he d pb-u but i would have to probably do a double integral (as pb-u combination is not fixed, and we can not simply do the error function calculation), so skipping that. but it is safe to say that we will have a lump of ~50% U, 44% pb, and 6% He (by mass), and a significant amount of he will remain in
probably the joke is that in simulations you have a lot of parameters, so even though code is same, not all of them would result in physically realistic situations. or your params were so bad that you ran out of memory or processes killed your system or shit, so even convergence bit works.