Tenn. Code Ann. § 31-7-110: Disclaimer by appointee, object, or taker in default of exercise of power of appointment

(a) A disclaimer of an interest in property by an appointee of a power of appointment takes effect as of the time the instrument by which the holder exercises the power becomes irrevocable.

(b) A disclaimer of an interest in property by a permissible appointee or taker in default of an exercise of a power of appointment takes effect as of the time the instrument creating the power becomes irrevocable.