Tex. Gov't Code § 824.407

If a beneficiary selects a life annuity death benefit under Section 824.402, the retirement system shall pay a lump-sum death benefit in an amount, if any, by which the amount of the deceased member's accumulated contributions at the time of death exceeds the amount of annuity payments made to the beneficiary before the beneficiary's death. This lump-sum benefit will be paid to the person designated by the beneficiary of the annuity or, if no person is designated, to the estate of the beneficiary.