Mo. Rev. Stat. § 87.315
The benefit reserve fund shall be the fund from which shall be paid all benefits except such benefits as involve only the refund of the members' contributions at time of withdrawal in which case the refund shall be made direct from the members' savings fund. There shall be transferred to this fund at time of approval of payment of benefits to any member or beneficiary, the accumulated contributions of such member from the members' savings fund and such additional amount from the general reserve fund as is calculated by the actuary to be necessary with the member's contributions to provide the payment of all benefits arising from the service of the member. Upon the completion of the first valuation after the creation of this fund, there shall be transferred to it from the annuity reserve fund, the pension reserve fund and the pension accumulation fund such amounts as are certified by the actuary on the basis of the tables then in use for all beneficiaries receiving benefits.
§ 87.315, RSMo