  A model for the production of large rapidity gaps being implemented in the
Monte Carlo event generator PHOJET is discussed. In this model, high-mass
diffraction dissociation exhibits properties similar to hadron production in
non-diffractive hadronic collisions at high energies. Hard diffraction is
described using leading-order QCD matrix elements together with a parton
distribution function for the pomeron and pomeron-flux factorization. Since
this factorization is imposed on Born graph level only, unitarity corrections
lead to a non-factorizing flux function. Rapidity gaps between jets are
obtained by soft color reconnection. It was previously shown that this model is
able to describe data on diffractive hadron production from the CERN-SPS
collider and from the HERA lepton-proton collider. In this work we focus on the
model predictions for rapidity gap events in p-p collisions at \sqrt{s} = 1800
GeV and compare to TEVATRON data.
