South Africa built its nuclear weapons at the Circle facility near Pretoria that was run by the South African armaments corporation Armscor (for more information, see "South Africa's Secret Nuclear Weapons"). The building contained a high security vault which stored highly enriched uranium (HEU) awaiting processing into weapon components and the finished nuclear weapons. South Africa also had other storage vaults for nuclear weapons, but these vaults were not used during the height of the program in the 1980s.

South African developed an elaborate set of security, safety, and control mechanisms over their nuclear weapons, prototypes, HEU, and test devices. This short report focuses on the storage of South Africa's nuclear weapons and the procedures, weapon design philosophy, and hardware that increased the ability to control access to these weapons. This information is drawn from ISIS archives and will be included in a ISIS report on South Africa's nuclear weapons program and its subsequent dismantlement. We are publishing this information now because of the potential lessons for Pakistan as it evaluates control mechanisms for its nuclear arsenal.

Control Philosophy

During the 1980s, South Africa developed nuclear weapons where separability was the key control philosophy. Each nuclear device was divided into a front and back section. The design minimized the possibility of accidental detonation or unauthorized use.

In essence, having a front and back half substituted for what the United States calls Permissive Action Links (PALS), devices that prevent the unauthorized use of nuclear weapons and typically are envisioned as part of the weapons themselves.

The South African design was a "gun-type" consisting of a target and projectile made of HEU. The front section contained the HEU target, but no electronics or safety systems. The back half contained the HEU projectile, the propellant, and firing systems. According to an Armscor official, a front and back end were never worked on simultaneously.

The HEU was also tightly controlled. At the beginning of each work day, the HEU scheduled for use in a manufacturing area was carefully weighed to the nearest 0.1 gram before being checked out of the vault. At the end of each day, the material was removed from the processing and manufacturing areas and weighed to a similar precision before being returned to the vault. HEU was not stored in process lines.

Access to the vault was tightly controlled. Based on a tour of Circle and the vault by Armscor officials given to ISIS staff in 1994, the control philosophy required ministerial approval, including the State President and other cabinet ministers, to get the front half out of a vault. The removal of the back end required four people with different codes. All four would have to be on-site. No one person had all four necessary codes. The four people had to include a military representative, someone from the Atomic Energy Corporation, and a senior Armscor official. Wide representation helped ensure that no one government entity could assemble the weapons itself.

Other control measures were also taken. There have been reports that the weapon itself contained controls.

Details of the Storage Vault

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Figures 1a-1c show the outer doors of the vault at Circle and the outer control panel.

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Inside the main vault are ten separate vaults on two levels (figures 2a-2d). A back and front half would not be stored in the same vault.

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The vault has an inner control panel that controls the ten inner doors (figures 3a-3b). A keypad can be seen.

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A control panel was also in the plant manager's office on the second floor of Circle (figure 4). He had video surveillance of the vault and had to approve access to the vault. We are unaware if he had to also punch in a code to allow the vault to open.

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Figure 5 is another picture of the outer vault door. In this case, wooden doors can be seen that would cover and hide the vault. These doors were placed over the vault after South Africa dismantled its nuclear weapons program in the early 1990s, but before it publicly announced that it had had a nuclear weapons program in 1993. During this interim period, Armscor was told to ensure that the weapons program could be denied if Circle was visited by outsiders.