Bismuth

''"Bismuth acts as post-RBMK gate, similar to Technetium with the difference that Technetium is also available from PWRs." <- THAT's what I needed to hear.''

The above tooltip has been since removed from Bismuth.

Bismuth is an extremely rare heavy element used to created Versatile Chipsets and other late-tier items. As the tooltip states, it is a post-RBMK gate.

Production
Bismuth is found in the decay chains of most nuclear waste, Short-Lived and Long-Lived Nuclear Waste, most of which consist of 15% Bismuth with a few exceptions, Neptunium Fuel produces absolutely no Bismuth and decayed Highly Enriched Plutonium-241 Fuel waste consists of 55% Bismuth.

Bismuth can be bred using Bismuth Zirconium Fast Breeders which yields 43. 3 % Bismuth fully depleted, with an initial investment of 1 Bismuth nugget per billet, making a total of 8 nuggets in investment per rod to potentially get ~20-21 nuggets (assuming normal distribution).

Bismuth can be obtained from decaying Lead-209.

Uses
Bismuth's has very specialized uses in Chipsets, as stated, which are used in the control cores of the Fusion Reactor, Fusionary Watz Plant, and even the Dark Fusion Core.

It is also used to make moderated fuel and control rods for the RBMK, which allows for more compact designs that use slow neutron fuels, SiOX Cancer Medication to eliminate Lung Diseases, the Magnetic Extractor to "milk" Duds, a tier 5 Anvil, and the Bismuth Pickaxe.

Trivia

 * IRL, Bismuth has numerous applications all varying from each other.
 * This includes medicine (Pepto- Bis mol), cosmetic pigmentations, alloys, and non-toxic Lead replacements.
 * As stated, it is used to replace Lead in some applications, this is due to it being relatively non-toxic, despite being a heavy element right between Lead and Polonium of all things.
 * Although non-radioactive in game and often considered so in many places, Bismuth is actually radioactive, just with a ridiculously long half-life.
 * Its half-life is 2.01×1019 years, which is 20,100,000,000,000,000,000 or twenty quintillion one hundred quadrillion years.
 * This is a relatively recent discovery, as this half-life is well over a billion times longer than the estimated age of the universe.
 * The (former) item description is yet another comment directed at Solstice.