Whenever any person is entitled under this part to lease for the period of 99 years, the department shall divide the term of 99 years into 2 periods of 50 and 49 years each, to be known as rental valuation periods, and the consideration or rental to be paid by the lessee for the first period of 50 years is to be determined by the department at the time such lessee is adjudged entitled to the lease. At the expiration of the first period of 50 years, the department shall redetermine the rental value or consideration to be paid by the lessee for the next succeeding rental period of 49 years until the expiration of the full term of the lease. However, the department, in determining the rental value to be paid by the lessee, shall consider the value of the land only and shall not increase the rental value or consideration for any of the rental periods because of the improvements that may have been made on any of the premises by a lessee. In determining the rental value or consideration to be paid by the lessee for the second valuation period of 49 years, the department shall not increase the rental value or consideration to any sum in excess of double the rental value or consideration determined for the first valuation period of 50 years. The consideration so fixed shall, as applied to the claimants coming within the provisions of this section, be a gross sum and not an annual rental.