By: Ian Sutherland

Watching a post-apocalyptic movie does not do justice to the experience of walking down the main road of the model Soviet town of Prypyat 30 years after it was evacuated in the aftermath of the Chernobyl nuclear power plant accident. What was once a spacious boulevard is now a forest hiding crumbling façades, a Ferris wheel stuck in time and vandalised classrooms – all abandoned, like the 188 settlements evacuated in the disaster’s aftermath.

On display in the National Chernobyl Museum, in Kiev, is a clock with its hands frozen at 01:23 – the time, on April 26, 1986, when the operator in the control room of Unit 4 pressed the emergency stop button and inadvertently triggered the runaway nuclear reaction, resulting in steam build-up that burst the reactor’s 3-m-thick, 2 000 t upper biological shield and spewed radioactive debris 9 km into the air.

In a desperate effort to contain the exposure and clean the affected areas after the explosion, the then Soviet authorities drafted up to 600 000 military and civilian personnel. These ‘liquidators’ cleared forests, removed topsoil, cleaned streets and buildings, shot domestic animals and buried radioactive trees and machinery. A concrete ‘sarcophagus’ was hastily constructed to cover the damaged reactor and prevent further spreading of radioactivity. To replace it, a French consortium, Novarka, is constructing the ‘New Safe Confinement’, to last for 100 years.

Only when standing a stone’s throw from the plant could I appreciate the immensity of this project. At 105 m high, 165 m long and spanning 260 m, the 30 000 t arched edifice of tubular steel will be the largest moveable land-based structure ever built.

To reduce worker exposure to radiation, it is being assembled away from the reactor and will be slid into position via rail. The enclosure will house remote-controlled cranes and other equipment to dismantle the existing sarcophagus and process the 200 t of radioactive material in the damaged reactor. After repeated delays, the $1.5-billion project is currently expected to be completed in 2017.

Chernobyl’s Unit 4 was powered by a RBMK1000 pressure-tube-type, light water-cooled uranium-graphite reactor. Ukranian National Chornobyl Museum notes that they were designed to be refuelled while in operation and without hermetically sealed shells. They were powerful, quick to build, easy to maintain and efficient – and led to the rapid expansion of the Soviet nuclear build programme in the 1970s and 1980s.

The accident happened during a planned shutdown to test the vibration characteristics of the plant’s turbogenerators in the event of a loss of power. The exact causes have been the subject of much debate. In their report to the International Atomic Energy Agency (IAEA) in Vienna in August 1986, the Soviets stated: “The prime cause of the accident was an extremely improbable combination of violations of instructions and operating rules committed by the staff.” Six plant managers were subsequently sentenced to prison.

Independent investigations, however, blamed inadequate procedures for operating at low power, a lack of automatic monitoring devices, oversteaming in the fuel channels, caused by a mismatch in coolant circulation, and reactor poisoning exacerbated by flaws in the design of the reactor’s control rods.

The West was alerted only two days after the accident, when instruments at a Swedish nuclear facility detected an enormous radioactive cloud spreading from Belarus and Ukraine. Though making international headlines on April 29, the only mention of the looming catastrophe in the Soviet Union was a statement by the Politburo on the bottom of the third page of a Ukrainian newspaper acknowledging that “one of the reactors is damaged”, while declaring that “measures to eliminate the consequences of the accident are taken”.

Firefighters extinguished the main fire within hours. Temperature in the core continued to rise, however, and the authorities began to fear a second explosion big enough to wipe out nearby cities and make most of Europe uninhabitable. They also worried that radioactive water would penetrate the slab beneath the reactor and contaminate the water table. To counter this, they ordered lead, in addition to sand and boric acid, to be dumped on the molten core from helicopters. A tunnel was also dug to drain and seal the reactor from below. These measures exposed emergency workers to lead poisoning and excessive radiation.

Thirty-six hours after the first explosion, the 43 000 inhabitants of Prypyat were told to gather their personal belongings – and three hours later the evacuation was complete. But, in Kiev, authorities allowed the May Day parade through the streets to continue, exposing thousands of civilians to harmful iodine radiation. Only on May 2 was the town of Chernobyl evacuated and the 10 km exclusion zone extended to the 30 km radius it is today.

Newer-generation nuclear reactors are safer, in part because of lessons learned from Chernobyl. Control rods were redesigned, reactor covers strengthened and plants automated. But whether the IAEA’s recommendations, including the need for “total psychological dedication to safety” by operators and a “nuclear safety culture at national level”, have been implemented is more difficult to determine.

The magnitude of the Chernobyl disaster is difficult to comprehend. It unleashed at least 100 times the radiation from the nuclear bombs that destroyed Hiroshima and Nagasaki. In Ukraine alone, 10% of the landmass was polluted and there are 3.5-million people today identified with the status of Chernobyl victims receiving medical and other benefits – the cost to the country being 5% to 7% of the annual State Budget.

The most harmful radionuclides released include iodine-31 (affecting the thyroid), strontium-90 (bone marrow) and caesium137 (soft tissue). Two workers died in the initial explosion, while 237 were diagnosed with acute radiation sickness and hospitalised in Moscow, where 28 died within three months. Estimates of ultimate fatalities range from 4 000 (World Health) to 100 000 (Greenpeace).

The question of when, if ever, the exclusion zone will be safe to resettle is contentious. Most of the radionuclides that were emitted have half-lives of less than 30 years and air dose rates above solid surfaces have largely returned to normal levels. However, heavier elements have accumulated in the ground, including Plutonium241, which decays into alpha emitter Americium241 with a half-life of 432 years. Some elderly residents, in defiance of regulations, repeatedly tried to return, until, in 1988, the authorities tacitly allowed 200 of them to resettle, of whom 157 remain. And, ironically, the absence of humans in the region has allowed populations of wildlife to flourish.

After touring this charming landscape of spring flowers, forests and ghost villages that surround the mortally wounded nuclear power plant, once the pride of Soviet technological prowess, it is impossible not to think of home. The South African government plans to build eight nuclear power stations, one close to Koeberg, 30 km north of Cape Town’s central business district. In the event of an accident of the scale of Chernobyl at either of these plants, much of the city would be rendered permanently uninhabitable. A sobering thought.

Sutherland is a mechanical engineer with an MBA in finance. he writes in his personal capacity - ian@sutherlandengineers.com