SA's 'small, safe' nuclear power
Charlie Schimdt
28 March 2006Climate change is just one of the problems linked to carbon-based fuels that have sparked a renewed interest in nuclear power. While stakeholders debate the merits of this approach, the nuclear industry and its supporters are exploring next-generation reactors that might be safer and less expensive than the ones used today. The pebble bed modular reactor (PBMR), which is based on a decades-old German design, ranks among the top contenders.
PBMR's supporters describe the technology as inherently safe and appropriate not just for rich, industrialised countries but also for developing nations. "The beauty of the pebble bed reactor is that you don't need an MIT PhD to run it," muses Andrew Kadak, a professor at the Massachusetts Institute of Technology's department of nuclear science and engineering. "That means you can use it even in countries that don't have the degree of history or background in nuclear technology that we have in Western Europe or here."
PBMR proponents point to another advantage: each reactor module generates about 170 megawatts of electrical power (MWe), far less than the 1 000 MWe produced by a standard light water reactor. PBMR can thus be scaled according to need: several modules can be connected in tandem to power a city, and one could supply the needs of a smaller town. Conceivably, the reactors could supply small, remote villages far from an urban electricity grid.
South Africa, which seeks a global role in next-generation nuclear technology, now leads PBMR's commercial development. The country expects to complete construction on a demonstration plant near Cape Town, a city of 3-million people, by 2010. What's more, the South African firm PBMR Pty, which is constructing the plant, ultimately hopes to build 30 pebble bed reactors throughout the country, says Jaco Kriek, the company's CEO. PBMR Pty is actively trying to license its technology in the US, and Westinghouse Electrical Co, owner of half the world's nuclear power plants, recently purchased a major stake in the company.
PBMR Pty also recently signed a memorandum of understanding with Chinergy, a Chinese company that plans to build its own demonstration plant near Beijing. China currently has the world's only operational PBMR plant - an experimental research model in Beijing housed at Tsinghua University. According to Kadak, who is collaborating on PBMR development with the scientists at Tsinghua University, China's long-term goals are to build PBMR plants throughout the country's interior. "The size is right for their needs," he explains.
How does it work?
The pebble bed design was first conceived in the 1950s by Rudolf Schulten, a physicist in Germany. Hoping to create a safer nuclear reactor, Schulten came up with a novel idea: he would pack tiny particles of uranium into thousands of graphite spheres, each about the size of a tennis ball. The radioactive balls, which
he called pebbles, could be cooled by helium gas, which would power a turbine as it flowed out of the reactor vessel. The uranium itself is sequestered at low density within the pebbles and shielded by their graphite casings. This ensures that the uranium can never get hot enough to melt, and the catastrophe of a nuclear meltdown can be avoided.
The idea took hold and, in the mid-1960s, scientists in Germany built a prototype pebble bed reactor that ran successfully for 21 years. A much larger, commercial-scale unit went online in the 1980s, but it was hobbled by design flaws and a growing environmental movement that shut down Germany's nuclear power industry altogether.
But even as PBMR technology was fading in Germany, it was re-emerging in South Africa, where industry and government officials thought its size and scalability were well suited for domestic power needs. Eskom, the largest South African utility company, bought rights to the PBMR design in 1993 and helped create PBMR Pty to advance the technology.
Now, at its R&D facility at Pelindaba, near the capital city Pretoria, PBMR Pty builds on the German design. The facility creates the reactor's pebbles by coating uranium dioxide fuel particles with alternating layers of carbon and silicon. The coated particles are pressed into mixtures of graphite powder and phenolic resin, which are machined into the characteristic spheres, each containing only about nine grams of uranium.
When operational, the reactor is designed to drop fresh pebbles into its core while used pebbles are extracted from below. After every cycle of the reactor, each pebble's residual fuel level will be measured electronically. PBMR officials predict that each of the 456 000 pebbles in a typical reactor will pass through the core six times over a period of three years.
The helium gas used to cool the core will get extremely hot - about 900°C, which is nearly three times the temperature produced in a typical light water reactor. This intense heat makes the reactor more efficient in terms of fuel-to-energy conversion, Kadak says. However, he adds that numerous design features ensure that the reactor never reaches the minimum of 3 000°C required to melt the core and unleash an environmental disaster.
For example, even if a failure occurs during operations, Kadak says, the reactor will come to a standstill and dissipate heat on a decreasing curve, without releasing radioactivity. Moreover, he adds that the helium cooling system and pebble design generate less nuclear waste than that produced by the light water reactors currently in use. A five-reactor PBMR generates nearly 1 000 MWe of power and five to six tons of depleted uranium per year, which is comparable to the output of a single light water reactor.
Environmentalists' challenge
Environmentalists aren't convinced, however. In January 2005, Earthlife Africa, an environmental group, convinced the Cape Town high court to rescind approval of the proposed plant, citing omissions in PBMR Pty's environmental impact statement. "This is a demonstration plant, and no one knows if it's even going to work," says Olivia Andrews, a campaign coordinator with Earthlife Africa in Cape Town. "The company is using us as guinea pigs." Andrews, who acknowledges that the group opposes all forms of nuclear power, claims PBMR Pty withheld information about higher-than-projected costs for the project. "PBMR is financially risky, and the company's feasibility studies are overly optimistic," she says.
Kriek acknowledges that in its early stages, PBMR won't compete cost-effectively with coal, but he suggests that economies of scale and engineering improvements will produce savings in the long term. "You have to understand the upfront costs for the technology are very large; we have over 50 PhDs in this company." He adds that a fresh public hearing process was launched in November 2005 and that the company plans to resubmit its environmental impact statement with additional disclosures as soon as possible.
The global outlook
During the next 25 years, PBMR Pty plans to export as many as 75 reactors in developed and developing markets, including other countries in Europe and Africa. Kadak anticipates that nuclear proliferation risks from global PBMR use could be controlled by the International Atomic Energy Agency through an a certification and oversight system to monitor operation and fuel handling. Used pebbles also constitute a poor source of material for nuclear terrorism, Kadak adds. The pebbles contain so little uranium - just nine grams each - that tens of thousands would be required to make a bomb. He emphasises that this is a detectable number.
"The grand vision is to create a global training centre for PBMR operations that would coordinate fuel supplies and waste disposal and also address problems related to infrastructure shortages," Kadak says.
Meanwhile, US officials with the Nuclear Regulatory Commission (NRC) are negotiating with PBMR Pty in efforts to certify the technology in the US. Some hope exists that the PBMR technology could become one of the Generation IV nuclear technologies that Bush administration officials in the US Department of Energy are trying to promote. The technologies are being sold as safe, economical, proliferation-resistant, and ready for prime time in the next 15 to 20 years.
NRC spokesperson Scott Burnell describes the PBMR's safety record as "interesting on a small scale." Although avoiding comment on how PBMR might fare as a Generation IV candidate, he concedes that NRC is closely watching its evolution in South Africa. But Kadak insists that PBMR is the best Generation IV candidate, not just because its modularity promotes siting flexibility; he says that the high temperatures at which it operates are well suited for electrolysis reactions that split hydrogen gas from water. Thus, he argues that PBMR could play a key role in fostering an emissions-free hydrogen economy, which many see as the ultimate solution to global warming.
Nevertheless, PBMR - like all nuclear technology - still faces nuclear-waste questions and worries over terrorism. The extent to which these concerns derail nuclear power and relegate its historical peak to the latter half of the 20th century remains to be seen.
Charlie Schimdt is a US-based freelance science and technology writer. He was recently in South Africa as a guest of the International Marketing Council of South Africa.
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