Procedures when adjacent control unit failed
 

Nei ho,

As far as i know, and that´s what we have set at my unit (Canarias ACC), if radar fails the old plain "conventional" procedures are to be followed. Flight plan strips, calculations and everybody to the holding pattern at assigned altitudes/FLs. Same applies to Enroute sectors: old conventional procedures, VOR separations and distance/minutes.

Best regards.

PD.- Or more likely you can fall in your knees and start to pray...

Sonnendec
Thanks for your information, we use ATC system called THALES which allowed us to use electronic flight progress strip, if radar failure happenen, there must be several aircraft only vertical separated and some aircraft are in same altitude but horizontal separated, so if cleared several aircraft to hold, it seems impossible especially in busy time. We are trying to figure out if there is a way to this problem.

You need an independent radar fallback system, if you don't have one you go for the Sonnendec way but, it depends by the traffic load, praying as first item could be required.
About the very first question, normally the ACC controller cannot take over the approach operations if he's not trained and qualified for; talking about Area Vs Area sometimes it should be possible within adjacent ACC-

Your first action should be to stop departures, and any other inbound traffic should be instructed to remain with the ACC. You could use emergency separation of 500ft, or the equivalent in metres, while you resolve the situation. You should make a general broadcast that the radar has failed, and pass traffic information where possible. After lots of co-ordination with adjacent radar units, you should be able to get some spatial awareness and then use procedural separations. As a last resort, TCAS should save the day.