Integrated tank for urea, vehicle provided with this tank and method for storing urea solutions on a vehicle

Storage system of urea solutions for vehicles provided with nitrogen oxides reduction systems for treating exhaust gases, including a fuel tank (1) and a tank for such solutions (4) housed in a cavity (5) inside the fuel tank. Vehicle provided with such system. Method for storing urea solutions in a system as described above, including the transfer of heat from the fuel to the solution.