Filter for removing radioactive noble gas, filter unit and reactor containment vent system

A radioactive noble gas removal filter comprising a polyimide film comprising a structural unit represented by a first formula:

• wherein, in the first formula,
• the N1 and the N2 each represent nitrogen,
• the R1 comprises at least one first aromatic ring,
• the R1 and the N1 form a first imide ring
• the R1 and the N2 form a second imide ring,
• a first steric structure of the at least one first aromatic ring, is disposed in a first plane, the first steric structure connecting a second steric structure of the first imide ring to a third steric structure of the second imide ring, wherein at least one of the second steric structure or the third steric structure is not coplanar with the first plane in which the first steric structure is disposed,
• the R2 comprises at least one second aromatic ring comprising an aromatic ring bonded to the N2,
• the at least one second aromatic ring to which the N2 is bonded comprises a first carbon atom bonded to the N2,
• the at least one second aromatic ring to which the N2 is bonded comprises a second carbon atom and a third carbon atom respectively at positions neighboring to the first carbon atom,
• at least one of the second carbon atom and the third carbon atom has a substituent,
• the third steric structure of the second imide ring to which the R2 is bonded and a fourth steric structure of the at least one second aromatic ring to which the N2 is bonded are not disposed on a same plane, and
• n represents an integer of one or greater.