Nullify all the gradient pointer setup for k-kL model
subroutine destroy_kkl_grad()
!< Nullify all the gradient pointer setup for k-kL model
implicit none
DebugCall('destroy_kkl_grad')
nullify(gradtk_x)
nullify(gradtkl_x)
nullify(gradtk_y)
nullify(gradtkl_y)
nullify(gradtk_z)
nullify(gradtkl_z)
end subroutine destroy_kkl_grad