The nuclear symbol for uranium-235 should be written as o U-235.
233
92 U
235
143 U
OU

²³⁵₉₂U

Explanation:

The nuclear symbol of the nuclei is ²³⁵₉₂U.

The uranium nuclei has;

          mass number  = 235

          atomic number  = 92

To write the structure of the atom;

         The subscript before the symbol of the atom is the atomic number

        The superscript is the mass number

So;

      ²³⁵₉₂U is the symbol of the nuclei.

it should have an internal chamber and two thermometers sticking out of the top. the internal chamber will also be closed off from the outside.