Upon his determination that the property, or any portion thereof, has ceased to be used in accordance with the applicable terms and conditions, the Secretary may terminate a right of use and occupancy. Nonpayment of property taxes, validly assessed, on any retained right of use and occupancy shall also be grounds for termination of such right by the Secretary. In the event the Secretary terminates a right of use and occupancy under this subsection he shall pay to the owners of the retained right so terminated an amount equal to the fair market value of the portion of said right which remained unexpired on the date of termination. With respect to any right of use and occupancy in existence on the effective date of this sentence, standards for retention of such rights in effect at the time such rights were reserved shall constitute the terms and conditions referred to in section
460u–3 of this title.