Shell-on Frozen Prawns and Power Outage
Without knowing the internal temperature of your freezer for the duration of the power outages this is impossible to answer.  Since these are planned outages, I assume you have experienced them before.  Do items in your freezer remain frozen?  At the very least, they will have experienced some freeze/thaw cycling, which would likely impact the texture of the prawns.  It is obviously not ideal. So, yes, I would be concerned.  How concerned is impossible to judge with the information provided.