Tenn. Code Ann. § 49-5-913: Management and investment of fund

(a) The board shall manage, lend, maintain, keep or deposit such funds for the benefit and uses of the public school teachers' retirement fund.

(b) The board shall receive all moneys from donations, legacies, gifts, bequests, and any surplus that may remain at the end of any fiscal year, from the sum or sums contributed and paid by both the teachers and by the school boards.

(c) The fund shall be invested in solvent and approved interest-bearing securities or well-secured mortgages or municipal bonds.