No concession contract shall be granted, the term of which exceeds six years, unless the concessionaire is required by the terms of the contract to expend major monetary sums for the purpose of improving, furnishing, equipping or enlarging existing facilities or constructing and/or furnishing additional facilities on the concession premises. In the event such major expenditures are made by a concessionaire, the term of his concession contract may be extended, but in no event exceed 12 years.