(a) Effect of construction orders
Any electric powerplant or major fuel-burning installation issued an order pursuant to section 792(c) of title 15 that is pending on the effective date of this chapter shall, notwithstanding the provisions of such section 792(c) or any other provision of this chapter, be subject to the provisions of this chapter as if it were a new electric powerplant or new major fuel-burning installation, as the case may be, except that if such order became final before such date, the provisions of subchapter II of this chapter shall not apply to such powerplant or installation.

(b) Effect of prohibition orders
The provisions of subchapters II and III shall not apply to any powerplant or installation for which an order issued pursuant to section 792(a) of title 15 before the effective date of this chapter is pending or final or which, on review, was held unlawful and set aside on the merits; except that any installation issued such an order under such section 792(a) which is pending on the effective date of this chapter may elect to be covered by subchapter II or III (as the case may be) rather than such section 792. Such an election shall be irrevocable and shall be made in such form and manner as the Secretary shall, within 90 days after November 9, 1978, prescribe. Such an election shall be made not later than 60 days after the date on which the Secretary prescribes the form and manner of making such election.

(c) Validity of orders
The preceding provisions of this chapter shall not affect the validity of any order issued under subsection (a), or any final order under subsection (c), of section 792 of title 15, and the authority of the Secretary to amend, repeal, rescind, modify, or enforce any such order, or rules applicable thereto, shall remain in effect notwithstanding any limitation of time otherwise applicable to such authority. Except as provided in this section, the authority of the Secretary under section 792 of title 15 shall terminate on the effective date of this chapter.