So you guys are sending students solo without briefing them on where they are to go in the event of the runway becoming blocked/airfield closed?
Yes, they are not yet capable of going anywhere else so why endanger them unnecessarily? ATC should be briefed that you are sending a student on a first solo, ideally the instructor will monitor (from the tower if possible). The probability of the airfield becoming unavailable in the duration of one circuit is very small. If the runway is blocked it is better that ATC get them down on the grass or a taxiway than expect them to divert.