Douglas Harper's Etymology Dictionary
unrepairable
1610s, from un- (1) "not" + repairable (adj.). Related: Unrepairably.
Wiktionary
unrepairable
a. Impossible to repair.
Usage examples of "unrepairable".
The general Ricky was dealing with told him to mark them off as unrepairable and keep them instead of paying the repair bills.
Besides, if one of the boats either capsized or became unrepairable, there was little the other crews could do.