I can definitely see graphite as being a very useful material to have in game, especially for the nuclear reactors and such, but we should also consider what other properties it could have as well, such as perhaps being a viable material for, say, producing a hypothetical steel element (For example, not saying a steel element should or shouldn't be added) using a powdered variant of graphite to mix in with the molten iron, things like electrical conductivity, melting points and such, whether it could be utilised for small scale batteries in saves and such, as graphite is definitely a fairly useful and versatile material.
Other things to consider would be what amount of pressure would be enough to change it to said powdered variant and whether said variant would share the moderation properties of the solid version, which I would assume it would.