No grant of franchise and no renewal, extension or amendment of such grant shall be valid unless it specifically reserves to the City the right, at intervals to be set forth in the franchise ordinance, to terminate the same by purchase or lease and operations of the property of the utility used in or conveniently useful for the operation of the utility in the streets of the City or elsewhere; nor shall any such grant, renewal or extension be valid which does not either definitely fix and determine the price which shall be paid by the City for the property of the public utility and the terms of payment in the event of purchase or lease by the City, or provide the precise means and methods whereby such purchase or rental price and terms shall be fixed and determined.