((a)) ** Authority for voluntary contributions**
((1)) ** In general** Under such regulations as may be prescribed by the Director, a participant may voluntarily contribute additional sums in multiples of one percent of the participant’s basic pay, but not in excess of 10 percent of such basic pay.
((2)) ** Interest** The voluntary contribution account in each case is the sum of unrefunded contributions, plus interest—
((A)) for periods before , at 3 percent a year; and
((B)) for periods on or after , at the rate computed under ,
((b)) ** Treatment of voluntary contributions** Effective on the date of retirement and at the election of the participant, the participant’s account shall be—
((1)) returned in a lump sum;
((2)) used to purchase an additional life annuity;
((3)) used to purchase an additional life annuity for the participant and to provide for a cash payment on the participant’s death to a beneficiary; or
((4)) used to purchase an additional life annuity for the participant and a life annuity commencing on the participant’s death payable to a beneficiary, with a guaranteed return to the beneficiary or the beneficiary’s legal representative of an amount equal to the cash payment referred to in paragraph (3).
((c)) ** Value of benefits** The benefits provided by subsection (b)(2), (3), or (4) shall be actuarially equivalent in value to the payment provided for in subsection (b)(1) and shall be calculated upon such tables of mortality as may be from time to time prescribed for this purpose by the Director.
((d)) ** Lump-sum payment** A voluntary contribution account shall be paid in a lump sum at such time as the participant dies or separates from the Agency without entitlement to an annuity. In the case of death, the account shall be paid in the order of precedence specified in .section 2071(c) of this title
((e)) ** Benefits in addition to other benefits** Any benefit payable to a participant or to the participant’s beneficiary with respect to the additional contributions provided under this section shall be in addition to benefits otherwise provided under this subchapter.