The three sacraments of Baptism, Confirmation, and Holy Orders confer, in addition to grace, a sacramental character or "seal" by which the Christian shares in Christ's priesthood and is made a member of the Church according to different states and functions. This configuration to Christ and to the Church, brought about by the Spirit, is indelible, it remains for ever in the Christian as a positive disposition for grace, a promise and guarantee of divine protection, and as a vocation to divine worship and to the service of the Church. Therefore these sacraments can never be repeated.
Source: Catechism of the Catholic Church (Vatican.va)