Upon death of a retired member, unless a reversionary annuity, widow's annuity or survivors annuity is payable, a death benefit shall be payable to such person as the member shall have nominated by written direction duly acknowledged and filed with the board or if no such nomination, to the estate of the member. Such benefit shall consist of the excess, if any, of the member's accumulated contributions plus credited interest still remaining in the system at the time of retirement, over the total amount of all retirement annuity payments received by the member prior to death subject to a minimum payment of $500.
40 ILCS 5/14-117