Clearance between the two parts of a double containmentGastight case around a reactor and the circuit and auxiliary... kept under negative pressure. In the case of leaks in the inner containmentGastight case around a reactor and the circuit and auxiliary..., radioactive substancesRadioactive substances within the meaning of the Atomic Ener... entering the annular gap are aspirated and either repumped or filtered and discharged via the vent stack in a controlled way.