  The role of direct URCA reactions in damping of the gravitational radiation
driven instability is discussed. The temperature at which bulk viscosity
suppresses completely this instability is calculated.
  The results are obtained analytically using recent calculations performed in
the case of bulk viscosity due to the modified URCA processes (Lindblom 1995;
Yoshida & Eriguchi 1995).
  The bulk viscosity caused by direct URCA reactions is found to reduce
significantly the region of temperatures and rotation frequencies where a
neutron star is subject to GRR instability.
