  A model for the QCD vacuum based on domain-like background gluon fields has
previously been developed and demonstrated to exhibit confinement of quarks and
strong correlation of the local chirality of quark modes and duality of the
background gluon field. On the boundary of the j-th domain, quark fluctuations
satisfy chirality violating boundary conditions parametrized by a chiral angle
$\alpha_j$ which is treated as a collective variable. The dependence of the
free energy of an ensemble of $N\to\infty$ domains on $\{\alpha_j, j=1... N\}$
is studied. For one massless flavour there are only two degenerate minima
($\alpha_j=0,\pi$ $\forall j$) due to the contribution of the anomaly to the
free energy, which suppresses the continuous U(1) degeneracy. The residual
discrete symmetry is spontaneously broken with a quark condensate of $-(238
{\rm{MeV}})^3.$ For $N_f$ massless flavours a continuous $SU(N_f)_L\times
SU(N_f)_R$ degeneracy appears, while the $U_A(1)$ direction remains suppressed.
