Hiroshima's residual radiation fell a millionfold in a week, and Chernobyl's contaminated zone has contracted for thirty years. The uranium in Gauteng's mine dumps does neither — and a licence condition could change that

DUARTE DA SILVA

Three kinds of radioactive ground

Radioactive ground is judged first by one question: how fast does it stop being radioactive? On that question Hiroshima, Chernobyl and the Witwatersrand sit at three different points on the scale, and the comparison explains why the mining belt's radiological record has never improved.

The Hiroshima bomb burst in the air. Most of its fission products rose and dispersed, and what it left in the ground was induced radioactivity in short-lived isotopes. By the city's own account, the dose a person would have received at the hypocentre fell to a thousandth of its first level within 24 hours and to a millionth within a week. The Radiation Effects Research Foundation's Life Span Study put the mean cumulative dose from that induced radiation, summed over all time, at probably less than 20–30 milligray. Hiroshima today reads at natural background.

Chernobyl was a reactor fire that released radionuclides over about ten days. Its long-term legacy is caesium-137 and strontium-90, with half-lives of 30.2 and 29.1 years. Physical decay alone lowers their concentrations by about 2% a year, before any countermeasure is applied. Chernobyl's contaminated land is getting cleaner by itself, slowly.

The Witwatersrand's radioactivity sits in the uranium-238 decay chain. Uranium-238 has a half-life of 4.468 billion years, thorium-230 about 75,000 and radium-226 1,600. For any planning purpose the decay rate is zero. The tailings hold something like 600,000 tonnes of uranium in six billion tonnes of sand, and untreated West Rand dumps run at 100 to 200 grams a tonne, 25 to 100 times ordinary crustal rock. Nothing in the Rand's inventory gets smaller unless someone takes it away.

The doses, side by side

In 1986 the Soviet authorities evacuated 116,317 people from 187 settlements around Chernobyl. Their average cumulative effective dose was 33 millisieverts. In 2010 the National Nuclear Regulator surveyed Tudor Shaft, a settlement on and beside a residue deposit near Krugersdorp, and reported a highest potential dose to residents of 3.9 millisieverts a year, about half of it external. At that rate a resident reaches the Chernobyl evacuees' average in eight and a half years, and the upper estimate of Hiroshima's all-time induced dose in under eight. Relocation was announced in February 2011. In October 2015, 197 families were still on the site. In October 2021, eighteen people were.

The comparison needs a caution, and the Ukrainian record supplies it. Ukraine's agricultural radiologists found that its calculated 'passport' internal doses ran on average about ten times higher than whole-body-counter measurements, and judged the zoning criteria too conservative. The regulator's 'potential' dose at Tudor Shaft is a conservative figure of the same family, and chronic doses of a few millisieverts a year are far below the level of acute harm. The weight of the comparison lies in who measured, how often, and what was done with the number.

Same pathways, a different poison

In the worst-hit regions of Ukraine, 70 to 95% of the population dose now comes from food, mostly milk. The regulator's Wonderfonteinspruit assessment, fieldwork for which was done at 47 sites in December 2006, was built on the same logic: fish, milk, meat, vegetables and water from a stream that runs past dairy farms and over the dolomitic aquifer that supplies towns. It found the dose to the most exposed group above the one-millisievert public limit at about half the sites on realistic pathways and three-quarters on potential ones, with calculated doses from 0.01 to 138 millisieverts a year. The Water Research Commission estimated that 46 tonnes of uranium a year enter the system, 34 of them off unlined tailings.

Uranium carries a hazard caesium lacks. Its drinking-water guideline of 30 micrograms a litre is set for chemical toxicity to the kidney, and Robinson Lake near Randfontein, declared a radiation area by the regulator, averaged 1,219 micrograms a litre between January 2004 and May 2005, forty times the guideline. The radium left in every dump gives off radon, a pathway Chernobyl's caesium does not create. In 2025 researchers found a median uranium level in the hair of children near tailings in Riverlea, Tshepisong and Snake Park twice that of children in Durban.

What two states did with the numbers

Ukraine legislated in 1991, five years after the accident. It drew four zones on dose and deposition, covering 2,293 settlements and, in 2007, 2.29 million people, 488,690 of them children under 14. Above one millisievert a year residents gained a guaranteed right to state-funded resettlement; above five, resettlement was compulsory. The state limed fields, reseeded pasture and fed cattle Prussian blue, and those countermeasures more than halved the internal dose. In Rivne oblast the settlements with a passport dose above one millisievert fell from 423 in 2001 to 25 in 2011. By 2022 no settlement outside the exclusion zone met the compulsory test.

South Africa's regulator held its 2006 survey back for three months and released it in August 2007 after the press had reported it. No basin-wide successor has been published. Gauteng classifies 157 residue areas covering 220 square kilometres as radioactive. The Auditor-General found in 2022 that none of the 2,322 high-risk gold, coal and copper mines on the derelict register had been rehabilitated, against a bill put at R48bn; this year's allocation is R140.87m. The acid-water plants run since 2012, rated at 229 megalitres a day, move uranium from water into sludge and leave the dumps that feed them untouched.

Why one map shrinks

Ukraine's map shrinks because its isotopes decay and its countermeasures work on food. Neither mechanism is available on the Rand. Fencing, grassing, neutralising and relocating act on the pathway and last only while someone pays for them. The source changes only by removal.

The basin has done that once, by accident. Nineteen uranium plants were built in four years from October 1952 to supply weapons programmes, and West Rand dumps from mines that ran them carry under 50 grams a tonne against 100 to 200 for their neighbours — the only large reduction in the inventory on record. The leach took the uranium and left the radium; tailings after extraction keep 70 to 90% of the ore's radioactivity, which is why removal has to be paired with a lined facility.

The capacity exists again. In February 2026 Sibanye-Stillwater declared a probable reserve of 25.2 million pounds of uranium oxide in its Cooke tailings, about 9,700 tonnes of uranium, and a plant is in environmental assessment. At 50% recovery it would take some 4,800 tonnes out of one dam, about 105 years of the Wonderfonteinspruit's estimated load. DRDGold moves 25 million tonnes a year from unlined dumps to lined facilities at full uranium grade; its chief executive said in August that uranium would need to add R60m in net profit to justify losing a hundredth of a gram of gold a tonne. As commerce, that is sound. As public health, it means the new facilities will be filled at full grade.

Three measures

None needs a new statute or fiscal money. Publish a basin-wide survey of uranium, radium and radon to a common standard, so the Rand has what Ukraine has had since 1991: a map with doses on it, repeated. Write into every certificate of registration the uranium grade reclaimed and deposited, with a closure provision that falls as the grade falls, so a tonne behind a liner at 50 grams costs its operator less than one at 150. And require the tonnes, grades, radium content and receptor doses to be published and audited each year.

The timing matters. The Cooke reserve was declared at a uranium price of $100 a pound, and spot stood at $89.68 at the end of August. The new facilities are being designed and licensed now, and a condition can shape them only before they are built. The basin has built uranium recovery three times since 1952 and dismantled it three times when the price fell.

Hiroshima's ground cleared itself in weeks. Chernobyl's is clearing at about 2% a year, with a law and a map to track it. The Rand's will clear only at the rate uranium is taken out of it, and at present that rate is zero.