There are hereby authorized to be appropriated to the Federal unemployment account, as repayable advances, such sums as may be necessary to carry out the purposes of this subchapter. Amounts appropriated as repayable advances shall be repaid by transfers from the Federal unemployment account to the general fund of the Treasury, at such times as the amount in the Federal unemployment account is determined by the Secretary of the Treasury, in consultation with the Secretary of Labor, to be adequate for such purpose. Any amount transferred as a repayment under this section shall be credited against, and shall operate to reduce, any balance of advances repayable under this section. Whenever, after the application of sections 1101(f)(3) and 1102(a) of this title with respect to the excess in the employment security administration account as of the close of any fiscal year, there remains any portion of such excess, so much of such remainder as does not exceed the balance of advances made pursuant to this section shall be transferred to the general fund of the Treasury and shall be credited against, and shall operate to reduce, such balance of advances. Amounts appropriated as repayable advances for purposes of this subsection shall bear interest at a rate equal to the average rate of interest, computed as of the end of the calendar month next preceding the date of such advance, borne by all interest bearing obligations of the United States then forming part of the public debt; except that in cases in which such average rate is not a multiple of one-eighth of 1 percent, the rate of interest shall be the multiple of one-eighth of 1 percent next lower than such average rate.