It cannot be repaid, ever, because the interest exceeds the amount of money that is currently in existence, which means they will always have to borrow more money (which is created out of thin air) to service the debt.
(It also wouldn't necessarily matter if the interest per year were greater than the total amount of money in existence. If the money supply were $20, that wouldn't make it impossible for me to pay you $21/year; I could pay it in 21 $1 payments.)