Opening and secure-closing system for doors comprising two doors (1,2) for accessing the interior of a chamber, which open towards the outside being hinged around two hinging axes (19,20), both doors (1,2) comprising a set of bolts (17,18) and the opening and closing system comprising additional means of opening/closing operation (26) and an overpressure door (3) located in one of the doors (1,2) which opens towards the outside, in such a way that the means of opening/closing operation (26) comprise a blocking bar (4), a blocking fitting (7) and means of retention (10) between the two doors (1,2) in order to provide a controlled and sequential opening/closing operation of the chamber, and the overpressure door (3) is opened automatically in the event of emergency due to overpressure, and it also participates in the controlled and sequential opening/closing operation of the chamber.