What does SVC TAR/SSR U/S mean?
What does svc tar/ssr u/s mean?

Terminal area surveillance radar and secondary surveillance radar (raw radar return and the secondary return from your transponder) is unserviceable. 

If you were VFR you could practice the approaches without ATC radar vectoring, or ATC could give you a non-radar routing via an airway, then transition route, then the instrument approach procedure.

In other words, the area for the time being (NOTAM period) has no radar.  Non-radar procedures would be utilized.  If the local ATC area was normally a radar environment and the radar equipment was taken down for preventive maintenance (for example), providing separation for practice approaches may be more than they are willing to do.

In the US ATC system, controllers are initially trained, tested, and qualified using a non-radar environment at the FAA Academy. Non-radar approach control is infrequently necessary in actual operation (unless it is in an area where radar coverage is not available full time, which is becoming rare in the US).  

Call the local ATC Approach Control in the area you are referring to and see what services they can provide.