The board of directors of the foundation may by resolution provide for the issuance of refunding bonds to refund any outstanding bonds issued under the Educational Assistance Act, together with redemption premiums, if any, and interest accrued or to accrue thereon. Provisions governing the issuance and sale of bonds under that act govern the issuance and sale of refunding bonds insofar as applicable. Refunding bonds may be exchanged for the outstanding bonds or may be sold and the proceeds used to retire the outstanding bonds. Pending the application of the proceeds of any such refunding bonds, with any other available funds, to the payment of the principal, interest and any redemption premiums on the bonds being refunded, and if so provided or permitted in the resolution of the foundation authorizing the issuance of such refunding bonds, to the payment of any interest on such refunding bonds and any expenses incurred in connection with such refunding, such proceeds may be placed in escrow and invested in securities which are unconditionally guaranteed by the United States and which shall mature or which shall be subject to redemption by the holders thereof, at the option of the holders, not later than the respective dates when the proceeds, together with the interest accruing thereon, will be required for the purposes intended.