To Catch a Falling Core: Lessons of Chernobyl for Russian Nuclear Industry

September 18, 2012|


Opening ceremony of Russia's AtomExpo 2012. Leonid Bolshov stands 4th from the left behind Rosatom chief Sergey Kirienko. Image by James Hill. Russia, 2012.

Russia's nuclear ambitions were on full display at "AtomExpo"—a three-day festival of international nuclear technology and conversation hosted by Rosatom, Russia's state-owned nuclear company, this past June in Moscow. Whether it was Fukushima's plant manager describing those first critical moments during the tsunami and the new thinking on "extreme" natural events or the myriad branches of the Rosatom empire showing off their wares at their slick booths, the message was clear: When it comes to nuclear, Russia is open for business.

The disastrous legacy of Chernobyl in Ukraine, where a Soviet-built reactor spectacularly blew up in 1986, is something of a PR problem, however. When Russia expressed interest in supplying the U.K. with 12 new reactors earlier this year, "immediately there appeared some articles with the headline 'Do you want another Chernobyl?' Sergei Novikov, Rosatom's spokesman, told me. "The phantoms of the Soviet period appear immediately."

Rosatom, though, is trying to spin the Chernobyl nightmare into a selling point: Who better to understand nuclear safety than the people who lived through the worst?

One of the biggest safety lessons of Chernobyl for Russian technology is a structure called a "core-catcher"—a steel vessel, water-cooled, built directly under a reactor to catch the molten reactor core in case of meltdown. The technology had been explored for years globally but had yet to be considered standard until Russia began adopting it after Chernobyl. In fact, physicist Leonid Bolshov, the man responsible for that design in those early days, has now become a leading Russian expert on nuclear safety. He is director of the Russian Academy of Sciences Nuclear Safety Institute, which he set up after Chernobyl heralding the beginning of Russia's cooperation with other countries on nuclear safety. His role at the time was considered so important after Chernobyl that he was issued one the few external fax lines in the Soviet Union so that he could communicate with other experts abroad.

Before the meltdown in 1986 Bolshov would have been an unlikely hero. A theoretical physicist with no prior nuclear experience, Bolshov didn't get the call for help until the Chernobyl reactor had already been melting down for five days. The challenge was to stop the hot core from potentially seeping into the ground or—worse—30 meters lower to water table, where radiation could potentially reach the Ukrainian capital Kiev and the Black Sea. "It was sort of a nightmare," Bolshov says.

"There was that Hollywood blockbuster called the China Syndrome and this same problem was exactly what we were trying to answer those first days in May," he recounted in his Moscow office earlier this year. "The Politburo was demanding a 100 percent guarantee of 'mitigation efficiency,' assuming that the fuel was inside, not outside the reactor, and calling for no further leaks into the air or earth. But this is contradictory," Bolshov says. "If you cover the source of the heat you decrease the cooling."

Two weeks of desperate chalkboard trial and error followed, as workers at the site were taking desperate and sometimes unsuccessful measures such as injecting liquid nitrogen into the soil to freeze it. Meanwhile, back in Moscow Bolshov and his team tried to calculate how fast the uranium dioxide fuel would melt compared with how fast they could carry away heat with some kind of coolant carried in pipes. But they had to figure out how to lay the pipes under a smoldering reactor. It was impossible to drill the soil under the reactor and pack the pipes densely enough to cool the melting fuel. What they needed were miners to install the pipes properly, but they also needed something to lower the temperature at the first moment the melting fuel touched the pipes, something with a high thermo-conductivity. The best candidate was graphite. But they would require vast amounts of this material.

"Those days were remarkable. In one day we collected enough graphite from all of the country. The regular bureaucratic system was in shock and it was possible to operate on science, on common sense. One call, a scrap of paper, and there were troops and heavy machinery on the move." Their final makeshift design was a snakelike formation of pipes cooled with water and covered on top with a thin graphite layer, all between two concrete layers—each one meter thick—to stabilize the creation. In short, Bolshov says, "it was done as a sandwich."

Bolshov's graphite-concrete "sandwich," similar in concept to "core-catchers" used in many nuclear reactor designs, paved the way for the ones Russia uses today—steel vessels filled with neutron-absorbing metallic alloys cooled by water flow and built directly under a reactor to catch the molten core material, known as "corium," in the case of meltdown. (A New York Times interview with Mr. Bolshov directly following the Fukushima disaster lays out more detail on the core-catcher's history and Russia's safety assurances in the post-Chernobyl marketplace).

Today many of Russia's potential customers for nuclear power plants are countries like Vietnam and Turkey, which are turning to nuclear for the first time and looking for cost-cutting perks the Russians can offer. In the case of Turkey, for instance, Russia is negotiating a plan called "Build–Own–Operate," in which it will finance and build four reactors in Turkey but retain ownership.

The reactor design of choice for these "nuclear newcomers," as Rosatom officials like to call them, is the VVER—Voda-Vodyanoi Energetichesky Reaktor, Russia's version of the pressurized water reactor, which has several indigenous distinctions from Western-designed reactors ranging from fuel assembly arrangements to a new passive residual heat-removal system, already being used in Russia and recently constructed in India. Russia has also built VVERs in Iran, China and across the former Eastern Bloc.

European regulators are increasingly requiring large new reactors to have some kind of core-catcher or similar device to trap melting reactor core, according to the World Nuclear Association. But other nuclear vendors have different approaches to protecting the bottom layers of nuclear plants. For example, in case of core melt, says Rosatom competitor Westinghouse's spokesman Scott Shaw, Westinghouse's AP1000 pressurized water reactors do not include core-catchers, yet compete for the same market the VVERs do. Instead, the former has a retention wall build into the reactor vessel itself, which he says would mitigate any core meltdown. In addition, an AP1000 operator "can act to flood the reactor cavity—the space immediately surrounding the reactor vessel—with water from the in-containment refueling water-storage tank, submerging the lower portion of the reactor vessel." The French company Areva also makes its EPR (for European Pressurized Reactor, or Evolutionary Power Reactor) with a core-catcher, helping it compete with the Russian VVER. Its device is focused on the idea of molten corium spreading along a sufficiently large area equipped with a special pipe system for basement cooling. But the Russians say their core-catchers are more compact and less costly than the European designs.

Russia's core-catchers have yet to be tested by a real-world China Syndrome. But there is some evidence that they might come in handy. During the Fukushima disaster one core "slumped" into the concrete beneath the reactor, which was built in the 1960s and did not have core-catcher, says Princeton physicist Frank von Hippel, a former assistant director for national security in the White House Office of Science and Technology Policy. The core leaked into the concrete below the reactor but did not breach the containment vessel.

"The Russians do know how to get things working, like they did in the space field," says Henry Sokolski of the Nonproliferation Policy Education Center, which presses lawmakers to take a closer look at the global spread of nuclear technology. "But sociologically and historically they have a lot working against them when it comes to quality assurance." Rosatom counters that they have independent oversight, a separate body in the government that answers to the prime minister on industrial safety, and that their models meet all International Atomic Energy Agency safety standards. (The IAEA encourages standards and guidelines but does not monitor compliance.)

The first Russian core-catcher was placed under China's Tianwan Nuclear Power Plant in 2007. Earlier this summer I looked into the pit of what will soon be the reactor vessel of one of two new VVER 1200-megawatt reactors under construction in Novovoronezh in southern Russia but couldn't see the core-catcher—it was already buried 4.45 meters below.

If Russia is successful in selling their post-Chernobyl nuclear technology, their core-catcher technology will be a key part of what's standing between their customers and another Chernobyl-like disaster. Whether it works in a real-life scenario remains an unanswered question. To use Bolshov's observation, we've had enough nuclear "nightmares" by now.