The maintenance of annuity reserves and pension reserves of the retirement system, the crediting of regular interest to the annuity savings fund, and the payment of all pensions, annuities, retirement allowances, refunds, and other benefits granted under this chapter shall be obligations of the pension accumulation fund. All assets of the pension accumulation fund and all income, interest, and dividends derived from deposits and investments shall be used for the payment of such obligations and for no other purpose.