Nullify all the gradient pointer setup for k-kL model
subroutine destroy_sst_grad()
!< Nullify all the gradient pointer setup for k-kL model
implicit none
DebugCall('destroy_sst_grad')
nullify(gradtk_x)
nullify(gradtw_x)
nullify(gradtk_y)
nullify(gradtw_y)
nullify(gradtk_z)
nullify(gradtw_z)
end subroutine destroy_sst_grad