10 July 1991
Foreign Minister R.F. (Pik) Botha signed accession to the Nuclear Non-proliferation Treaty (NPT) on behalf of South Africa. This opened South Africa's nuclear facilities for inspection. South Africa became the first nation in history to ever rollback its nuclear capability. Nuclear rollback occurs when a nation voluntarily achieves one or more of the following: eliminates its nuclear weapons, relinquishes at least some of the technical means to acquire nuclear weapons, or accepts a control regime to prevent it from going nuclear. The nuclear safeguards agreement entered into force on 16 September 1991.
References

Country Profile, South Africa,(2013),Nuclear, February[online],Available at www.nti.org [Accessed:9 July 2013]