The Commission is authorized in connection with the construction or operation of the Oak Ridge, Paducah, and Portsmouth installations of the Commission, without regard to sections 1341, 1342, and 1349-1351 and subchapter II of chapter 15 of title 31, to enter into new contracts or modify or confirm existing contracts to provide for electric utility services for periods not exceeding twenty-five years, and such contracts shall be subject to termination by the Commission upon payment of cancellation costs as provided in such contracts, and any appropriation presently or hereafter made available to the Commission shall be available for the payment of such cancellation costs. Any such cancellation payments shall be taken into consideration in determination of the rate to be charged in the event the Commission or any other agency of the Federal Government shall purchase electric utility services from the contractor subsequent to the cancellation and during the life of the original contract. The authority of the Commission under this section to enter into new contracts or modify or confirm existing contracts to provide for electric utility services includes, in case such electric utility services are to be furnished to the Commission by the Tennessee Valley Authority, authority to contract with any person to furnish electric utility services to the Tennessee Valley Authority in replacement thereof. Any contract hereafter entered into by the Commission pursuant to this section shall be submitted to the Energy Committees and a period of thirty days shall elapse while Congress is in session (in computing such thirty days, there shall be excluded the days on which either House is not in session because of adjournment for more than three days) before the contract of the Commission shall become effective: Provided, however, That the Energy Committees, after having received the proposed contract, may by resolution in writing, waive the conditions of or all or any portion of such thirty-day period.