As for the first part of your question, why South Africa pursued a nuclear weapons program: This is difficult to answer, because there where a number of reasons feeding into this. Firstly, the Apartheid state had an extremely string modernizing tendency in itself and therefore was likely to develop nuclear technologies just out of these tendencies. The Apartheid state saw itself as a developed (white) nation and as Nuclear technology was the peak technology of the time generating cheap energy, it was obligatory in order to confirm this self-proclaimed status. Additionally, nuclear weapons were the main signifier for geopolitical power in this time and as Apartheid S.A. had ambitions of panafrican domination/representation nuclear weapons were key to the ascertion of this position. The South African whites, ruling the state also saw themselves encircled by enemy groups both within (the black majority population) and outside strong communist liberstion movements in Angola (neighbouring at the time sa- occupied Namibia, Rhodesia (no Zimbabwe and Zambia ) and Mozambique. These communist movements in the neighbouring states might also have been a reason that the US seemed to be inclined to tolerate the clear entichment of weaponized uranium and plutonium within their program that was aimed at offering civil nuclear technologies to other nations (see Truman doctrine for the geopolitical reasoning).

As for the second part of your question why they dropped the technology: In the 1980s, suffering under economic and political sanctions from the majority of the international community and facing strikes and mass uprisings it became clear to the leadership of the Apartheid state that they would have to abdicate and turn government over to the African National Congress (ANC) and the tripartite government. In order to prevent a black, African socialist government to obtain nuclear weapons, they opted to initiate a program to destroy their nuclear arsenal before handing over the government.

I studied sociology at the University of Pretoria and I'd be happy to answer any follow up question supply you with source material/further reading on any of the aspects described here if needed.

There is no simple easy answer to "why'd they pursue them." They are one of the cases where the "security explanation" (e.g., "they got them to deter another power") doesn't totally hold up. There were certainly fears of Soviet-encouraged anti-colonial movements in Africa (notably Angola), and a generalized paranoia that came with being an increasingly isolated, explicitly racist regime on continent increasingly opposed to white colonial rule. But most internal accounts suggest a sort of slow institutional inertia, in which the capability to go nuclear was pursued at a moderate pace, often encouraged by the powerful South African mining industry (which was mining uranium) in league with their nuclear science agency, both of whom sought the prestige and funding that would come with such a program. It is not even entirely clear when the decision to produce weapons was made — sometime between 1974 and 1977. It's a vague mess, made even vaguer by the high amount of internal secrecy they surrounded it with. It appears to lack the decisive feature of most other nuclear programs (in which at some point, some high leader said, "this is our #1 national priority" and so forth).

This lack of strong institutional and discursive support for the program, which never resulted in most than half a dozen bombs or so, no doubt played a role in its ability to suddenly evaporate once de Klerk decided to get rid of it: it was not large, its purpose was never clear, it was more of a liability than an asset, and the number of state actors who were in favor of it were relatively small, at least compared to the nuclear arsenals of other states.

A very useful article on this is Peter Liberman, "The Rise and Fall of the South African Bomb," International Security 26, no. 2 (Fall 2001), 45-86.

Though not specifically talking about the South African nuclear program, Gavin Cawthra's 1985 "Brutal Force: The Apartheid War Machine" paints the picture of a largely paranoid "securocratic state". Central to South Africa's foreign and defence policy at the time was the idea of "total onslaught", which had been first articulated in the P.W. Botha's 1978 Defence White paper, while he was still the Defence minister of South Africa. The concept of total onslaught envisioned South Africa as a country surrounded and under siege, and was often used to justify the country's ballooning defence spending, ever growing secret defence account, and omnipresent military. As a result, the decision to pursue nuclear weapons by the South African state can be at least partially explained by their desire to ensure total regime survival. As Cawthra explains, by 1985, the number of attacks by both SWAPO in Namibia, and the Umkhonto we Sizewe in South Africa proper, had spiked, which led to the declaration of the state of emergency. Consequently, the state was under increasing strain, and sought to look for ways to preserve its existence.

Another aspect of their decision to nuclearize relates to their alliance with Israel and Taiwan. A lot of information on South Africa's illegal sanction busting activities and unofficial foreign relations, can be found in the excellent "Apartheid: Guns and Money" by Hennie van Vuuren. Though there is less knowledge about Taiwan's role, Israeli and South African scientists cooperated closely, to the extent that the nuclear test which would become the Vela Incident in 1979 was largely an Israel hydrogen bomb "proof of concept" test, with the South Africans and Taiwanese observing. In fact, the test was conducted on South African ships all of whom carried large numbers of Israelis. It is unknown what Taiwan's full role was in the test was, however, according to the Soviet Spy, Dieter Gerhardt, commander of the Simon's Town Naval base, at the time of the test, a Taiwanese warship had docked in the harbour for unknown business (which is unusual given that he should have been privy to their actions as commander of the base). What this illustrates is that another prominent reason for nuclearization in South Africa stemmed from the pressures of SA's allies who also had their own reasons to acquire nuclear weapons, but did not possess the necessary geography to conduct advanced tests.

Though not specifically talking about the South African nuclear program, Gavin Cawthra's 1985 "Brutal Force: The Apartheid War Machine" paints the picture of a largely paranoid "securocratic state". Central to South Africa's foreign and defence policy at the time was the idea of "total onslaught", which had been first articulated in the P.W. Botha's 1978 Defence White paper, while he was still the Defence minister of South Africa. The concept of total onslaught envisioned South Africa as a country surrounded and under siege, and was often used to justify the country's ballooning defence spending, ever growing secret defence account, and omnipresent military. As a result, the decision to pursue nuclear weapons by the South African state can be at least partially explained by their desire to ensure total regime survival. As Cawthra explains, by 1985, the number of attacks by both SWAPO in Namibia, and the Umkhonto we Sizewe in South Africa proper, had spiked, which led to the declaration of the state of emergency. Consequently, the state was under increasing strain, and sought to look for ways to preserve its existence.

Another aspect of their decision to nuclearize relates to their alliance with Israel and Taiwan. A lot of information on South Africa's illegal sanction busting activities and unofficial foreign relations, can be found in the excellent "Apartheid: Guns and Money" by Hennie van Vuuren. Though there is less knowledge about Taiwan's role, Israeli and South African scientists cooperated closely, to the extent that the nuclear test which would become the Vela Incident in 1979 was largely an Israel hydrogen bomb "proof of concept" test, with the South Africans and Taiwanese observing. In fact, the test was conducted on South African ships all of whom carried large numbers of Israelis. It is unknown what Taiwan's full role was in the test was, however, according to the Soviet Spy, Dieter Gerhardt, commander of the Simon's Town Naval base, at the time of the test, a Taiwanese warship had docked in the harbour for unknown business (which is unusual given that he should have been privy to their actions as commander of the base). What this illustrates is that another prominent reason for nuclearization in South Africa stemmed from the pressures of SA's allies who also had their own reasons to acquire nuclear weapons, but did not possess the necessary geography to conduct advanced tests.

Though not specifically talking about the South African nuclear program, Gavin Cawthra's 1985 "Brutal Force: The Apartheid War Machine" paints the picture of a largely paranoid "securocratic state". Central to South Africa's foreign and defence policy at the time was the idea of "total onslaught", which had been first articulated in the P.W. Botha's 1978 Defence White paper, while he was still the Defence minister of South Africa. The concept of total onslaught envisioned South Africa as a country surrounded and under siege, and was often used to justify the country's ballooning defence spending, ever growing secret defence account, and omnipresent military. As a result, the decision to pursue nuclear weapons by the South African state can be at least partially explained by their desire to ensure total regime survival. As Cawthra explains, by 1985, the number of attacks by both SWAPO in Namibia, and the Umkhonto we Sizewe in South Africa proper, had spiked, which led to the declaration of the state of emergency. Consequently, the state was under increasing strain, and sought to look for ways to preserve its existence.

Another aspect of their decision to nuclearize relates to their alliance with Israel and Taiwan. A lot of information on South Africa's illegal sanction busting activities and unofficial foreign relations, can be found in the excellent "Apartheid: Guns and Money" by Hennie van Vuuren. Though there is less knowledge about Taiwan's role, Israeli and South African scientists cooperated closely, to the extent that the nuclear test which would become the Vela Incident in 1979 was largely an Israel hydrogen bomb "proof of concept" test, with the South Africans and Taiwanese observing. In fact, the test was conducted on South African ships all of whom carried large numbers of Israelis. It is unknown what Taiwan's full role was in the test was, however, according to the Soviet Spy, Dieter Gerhardt, commander of the Simon's Town Naval base, at the time of the test, a Taiwanese warship had docked in the harbour for unknown business (which is unusual given that he should have been privy to their actions as commander of the base). What this illustrates is that another prominent reason for nuclearization in South Africa stemmed from the pressures of SA's allies who also had their own reasons to acquire nuclear weapons, but did not possess the necessary geography to conduct advanced tests.

Though not specifically talking about the South African nuclear program, Gavin Cawthra's 1985 "Brutal Force: The Apartheid War Machine" paints the picture of a largely paranoid "securocratic state". Central to South Africa's foreign and defence policy at the time was the idea of "total onslaught", which had been first articulated in the P.W. Botha's 1978 Defence White paper, while he was still the Defence minister of South Africa. The concept of total onslaught envisioned South Africa as a country surrounded and under siege, and was often used to justify the country's ballooning defence spending, ever growing secret defence account, and omnipresent military. As a result, the decision to pursue nuclear weapons by the South African state can be at least partially explained by their desire to ensure total regime survival. As Cawthra explains, by 1985, the number of attacks by both SWAPO in Namibia, and the Umkhonto we Sizewe in South Africa proper, had spiked, which led to the declaration of the state of emergency. Consequently, the state was under increasing strain, and sought to look for ways to preserve its existence.

Another aspect of their decision to nuclearize relates to their alliance with Israel and Taiwan. A lot of information on South Africa's illegal sanction busting activities and unofficial foreign relations, can be found in the excellent "Apartheid: Guns and Money" by Hennie van Vuuren. Though there is less knowledge about Taiwan's role, Israeli and South African scientists cooperated closely, to the extent that the nuclear test which would become the Vela Incident in 1979 was largely an Israel hydrogen bomb "proof of concept" test, with the South Africans and Taiwanese observing. In fact, the test was conducted on South African ships all of whom carried large numbers of Israelis. It is unknown what Taiwan's full role was in the test was, however, according to the Soviet Spy, Dieter Gerhardt, commander of the Simon's Town Naval base, at the time of the test, a Taiwanese warship had docked in the harbour for unknown business (which is unusual given that he should have been privy to their actions as commander of the base). What this illustrates is that another prominent reason for nuclearization in South Africa stemmed from the pressures of SA's allies who also had their own reasons to acquire nuclear weapons, but did not possess the necessary geography to conduct advanced tests.

Though not specifically talking about the South African nuclear program, Gavin Cawthra's 1985 "Brutal Force: The Apartheid War Machine" paints the picture of a largely paranoid "securocratic state". Central to South Africa's foreign and defence policy at the time was the idea of "total onslaught", which had been first articulated in the P.W. Botha's 1978 Defence White paper, while he was still the Defence minister of South Africa. The concept of total onslaught envisioned South Africa as a country surrounded and under siege, and was often used to justify the country's ballooning defence spending, ever growing secret defence account, and omnipresent military. As a result, the decision to pursue nuclear weapons by the South African state can be at least partially explained by their desire to ensure total regime survival. As Cawthra explains, by 1985, the number of attacks by both SWAPO in Namibia, and the Umkhonto we Sizewe in South Africa proper, had spiked, which led to the declaration of the state of emergency. Consequently, the state was under increasing strain, and sought to look for ways to preserve its existence.

Another aspect of their decision to nuclearize relates to their alliance with Israel and Taiwan. A lot of information on South Africa's illegal sanction busting activities and unofficial foreign relations, can be found in the excellent "Apartheid: Guns and Money" by Hennie van Vuuren. Though there is less knowledge about Taiwan's role, Israeli and South African scientists cooperated closely, to the extent that the nuclear test which would become the Vela Incident in 1979 was largely an Israel hydrogen bomb "proof of concept" test, with the South Africans and Taiwanese observing. In fact, the test was conducted on South African ships all of whom carried large numbers of Israelis. It is unknown what Taiwan's full role was in the test was, however, according to the Soviet Spy, Dieter Gerhardt, commander of the Simon's Town Naval base, at the time of the test, a Taiwanese warship had docked in the harbour for unknown business (which is unusual given that he should have been privy to their actions as commander of the base). What this illustrates is that another prominent reason for nuclearization in South Africa stemmed from the pressures of SA's allies who also had their own reasons to acquire nuclear weapons, but did not possess the necessary geography to conduct advanced tests.

Though not specifically talking about the South African nuclear program, Gavin Cawthra's 1985 "Brutal Force: The Apartheid War Machine" paints the picture of a largely paranoid "securocratic state". Central to South Africa's foreign and defence policy at the time was the idea of "total onslaught", which had been first articulated in the P.W. Botha's 1978 Defence White paper, while he was still the Defence minister of South Africa. The concept of total onslaught envisioned South Africa as a country surrounded and under siege, and was often used to justify the country's ballooning defence spending, ever growing secret defence account, and omnipresent military. As a result, the decision to pursue nuclear weapons by the South African state can be at least partially explained by their desire to ensure total regime survival. As Cawthra explains, by 1985, the number of attacks by both SWAPO in Namibia, and the Umkhonto we Sizewe in South Africa proper, had spiked, which led to the declaration of the state of emergency. Consequently, the state was under increasing strain, and sought to look for ways to preserve its existence.

Another aspect of their decision to nuclearize relates to their alliance with Israel and Taiwan. A lot of information on South Africa's illegal sanction busting activities and unofficial foreign relations, can be found in the excellent "Apartheid: Guns and Money" by Hennie van Vuuren. Though there is less knowledge about Taiwan's role, Israeli and South African scientists cooperated closely, to the extent that the nuclear test which would become the Vela Incident in 1979 was largely an Israel hydrogen bomb "proof of concept" test, with the South Africans and Taiwanese observing. In fact, the test was conducted on South African ships all of whom carried large numbers of Israelis. It is unknown what Taiwan's full role was in the test was, however, according to the Soviet Spy, Dieter Gerhardt, commander of the Simon's Town Naval base, at the time of the test, a Taiwanese warship had docked in the harbour for unknown business (which is unusual given that he should have been privy to their actions as commander of the base). What this illustrates is that another prominent reason for nuclearization in South Africa stemmed from the pressures of SA's allies who also had their own reasons to acquire nuclear weapons, but did not possess the necessary geography to conduct advanced tests.

Though not specifically talking about the South African nuclear program, Gavin Cawthra's 1985 "Brutal Force: The Apartheid War Machine" paints the picture of a largely paranoid "securocratic state". Central to South Africa's foreign and defence policy at the time was the idea of "total onslaught", which had been first articulated in the P.W. Botha's 1978 Defence White paper, while he was still the Defence minister of South Africa. The concept of total onslaught envisioned South Africa as a country surrounded and under siege, and was often used to justify the country's ballooning defence spending, ever growing secret defence account, and omnipresent military. As a result, the decision to pursue nuclear weapons by the South African state can be at least partially explained by their desire to ensure total regime survival. As Cawthra explains, by 1985, the number of attacks by both SWAPO in Namibia, and the Umkhonto we Sizewe in South Africa proper, had spiked, which led to the declaration of the state of emergency. Consequently, the state was under increasing strain, and sought to look for ways to preserve its existence.

Another aspect of their decision to nuclearize relates to their alliance with Israel and Taiwan. A lot of information on South Africa's illegal sanction busting activities and unofficial foreign relations, can be found in the excellent "Apartheid: Guns and Money" by Hennie van Vuuren. Though there is less knowledge about Taiwan's role, Israeli and South African scientists cooperated closely, to the extent that the nuclear test which would become the Vela Incident in 1979 was largely an Israel hydrogen bomb "proof of concept" test, with the South Africans and Taiwanese observing. In fact, the test was conducted by Israeli warships, not South African ones. It is unknown what Taiwan's full role was in the test was, however, according to the Soviet Spy, Dieter Gerhardt, commander of the Simon's Town Naval base, at the time of the test, a Taiwanese warship had docked in the harbour for unknown business (which is unusual given that he should have been privy to their actions as commander of the base). What this illustrates is that another prominent reason for nuclearization in South Africa stemmed from the pressures of SA's allies who also had their own reasons to acquire nuclear weapons, but did not possess the necessary geography to conduct advanced tests.