Molybdenum-99, or Mo-99, is used in millions of diagnostic tests for cancer, heart disease and other illnesses worldwide.
NTP Radioisotopes is a subsidiary of the South African Nuclear Energy Corporation (Necsa) and uses the 20 megawatt Safari 1 research reactor at Pelindaba, in operation since 1965, to produce Mo-99.
The plant had to be shutdown for three months at the beginning of 2018 after a hydrogen leak was detected.
It is currently in care and maintenance, Necsa said, as it released a request for information (RFI) to the market on Monday, the first step in a tender process to help gauge appetite from a potential preferred supplier to construct a new multi-purpose reactor (MPR).
"The MPR will continue with the legacy of producing medical radioisotopes, which are used to treat thousands of patients diagnosed with cancer all over the world," Loyiso Tyabashe, group chief executive at Necsa, said in a statement.
The NTP is a top four global supplier of medical radioisotopes to the United States, Japan and countries in Europe and the Middle East, Necsa said.
The request for information ends on 10 March, the company added.