  The orbital evolution of a binary system consisting of two primordial black
hole clusters is investigated. Such clusters are predicted in some theoretical
models with broken symmetry in the inflation Lagrangian. A cluster consists of
the most massive central black hole surrounded by many smaller black holes.
Similar to single primordial black holes, clusters can form gravitationally
bounded pairs and merge during their orbital evolution. The replacement of
single black holes by such clusters significantly changes the entire merger
process and the final rate of gravitational wave bursts in some parameter
ranges (with sufficiently large cluster radii). A new important factor is the
tidal gravitational interaction of the clusters. It leads to an additional
dissipation of the orbital energy, which is transferred into the internal
energy of the clusters or carried away by black holes flying out of the
clusters. Comparison with the data of gravitational-wave telescopes allows one
to constrain the fractions of primordial black holes in clusters, depending on
their mass and compactness. Even the primordial black hole fraction in the
composition of dark matter $\simeq1$ turns out to be compatible with LIGO/Virgo
observational data, if the black holes are in clusters.
