Tenn. R. Civ. P. 47.02

The court may direct prior to the start of jury selection that one or more jurors in addition to the regular jury of twelve persons be called and impaneled. The additional jurors shall be drawn in the same manner, shall have the same qualifications, shall be subject to the same examination and challenges, shall take the same oath, and shall have the same functions, powers, facilities, and privileges as the regular jurors. If one or more additional jurors are called, each party is entitled to one peremptory challenge for each such additional juror, up to the maximum provided by law. Such additional peremptory challenges may be used against any regular or additional juror. The trial court in its discretion may use either of the following methods to select and impanel additional jurors:

(1) During the jury selection or the trial of the case, there shall be no distinction made by the court as to which jurors are additional jurors and which jurors are regular jurors. Before the jury retires to consider its verdict, the court shall select by lot the names of the requisite number of jurors to reduce the jury to a body of twelve or such other number as the law provides. A juror who is not selected to be a member of the final jury shall be discharged when that jury retires to consider its verdict.

(2) Following the selection of the jury of twelve regular jurors or such other number as the law provides, the additional jurors shall be selected and impaneled as alternate jurors. Alternate jurors, in the order in which they are called, shall replace regular jurors who, prior to the time the jury retires to consider its verdict, become unable or disqualified to perform their duties prior to the time the jury retires to consider its verdict. An alternate juror who does not replace a regular juror shall be discharged when the jury retires to consider its verdict.