These exist. They are not uranium; they are just small (~1 cm) metal blocks. They store a lot of heat, and so when heated in warm water for a while and then placed in coffee, they keep the coffee warp for a very long time. They also can be placed in the freezer and made to be reusable ice cubes. I own several. They're much more fun and much more compact than a bulky thermos flask.

Do not put uranium anywhere close to anything you plan to eat/eat off of, even if it's shielded. Uranium is not only radioactive but extremely toxic and any impurities on the outside or flaws in the shielding will mean you are ingesting raw uranium, which would probably be fatal given how toxic polonium can be.

These exist. They are not uranium; they are just small (~1 cm) metal blocks. They store a lot of heat, and so when heated in warm water for a while and then placed in coffee, they keep the coffee warm for a very long time. They also can be placed in the freezer and made to be reusable ice cubes. I own several. They're much more fun and much more compact than a bulky thermos flask.

Do not put uranium anywhere close to anything you plan to eat/eat off of, even if it's shielded. Uranium is not only radioactive but extremely toxic and any impurities on the outside or flaws in the shielding will mean you are ingesting raw uranium, which would probably be fatal given how toxic polonium can be.