The bonds shall bear interest at a rate not to exceed 8 percent per year to be fixed by the board, except that, if, before the issuance of the bonds, the board determines, to the best of its knowledge and belief, that the interest on the bonds will be subject to federal income taxation under then existing law, the bonds may bear interest at a rate or rates not exceeding 10 percent per year to be fixed by the board.
This section shall become operative on January 1, 1984.