Amounts deducted and withheld from basic salary of a participant under section
4045 of this title from the beginning of the first pay period after the participant has completed 35 years of service computed under section
4056 of this title (excluding service credit for unused sick leave under section
4056
(b) of this title), together with interest on the amounts at the rate of 3 percent a year compounded annually from the date of the deduction to the date of retirement or death, shall be applied toward any special contribution due under section
4045
(d) of this title), and any balance not so required shall be refunded in a lump sum to the participant after separation or, in the event of a death in service, to a beneficiary in the order of precedence specified in subsection (f) of this section.