New Scientist, October 28, 2006

Tougher controls on the slaughter of sheep have been imposed in Norway after they were found to be contaminated with unusually high levels of radioactivity from the Chernobyl disaster in 1986.
The Norwegian Radiation Protection Authority (NRPA) says the problem has arisen because the sheep have feasted on an unusually large crop of mushrooms, which were more plentiful than usual because of wet weather. Previous research has shown that fungi take up more radioactivity from the soil than grasses or other plants.

Could mushrooms like these Norwegian ceps also be dangerous to humans?
There are 36 areas of upland Norway where Chernobyl contamination still requires controls on sheep. According to the NRPA, levels of caesium-137 from the Chernobyl disaster reached 7000 becquerels per kilogram in sheep this year, more than twice maximum levels in previous years.
Farmers can reduce the level of radioactivity in sheep by giving them non-contaminated food for a month before slaughter. For some farmers, this period will now have to be doubled to reduce caesium-137 levels to below Norway’s safety limit of 600 bq/kg.
Per Strand, the NRPA’s head of environmental radioactivity, stresses that the precautions mean that lamb on the market is safe to eat. He says, though, that the discovery of such high levels of radioactivity so long after the Chernobyl accident came as a surprise.
“No one at the time expected contamination to be so high more than 20 years after the event,” he says.
From issue 2575 of New Scientist magazine, 28 October 2006, page 7

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Rebekah Kendal, iAfrica.com, October 19 2006

There’s something vaguely scary about the notion of nuclear power. Images of Chernobyl, nuclear weapons and all the horror that they convey all too often spring to mind when we talk about nuclear energy.
But with an energy crisis looming in South Africa — and the possibility of blackouts becoming the norm — the government has announced an ambitious plan to build at least 24 ‘mini’ nuclear power stations, called Pebble Bed Modular Reactors.
But do we really need them, how do they work, and should we be alarmed?
Energy crisis
In order to understand the ‘why’ of it all, you have to begin by examining the energy situation in South Africa. At the moment, Eskom supplies 95 percent of South Africa’s energy and 60 percent of Africa’s energy. At its current rate the demand for electricity is expected to exceed the supply by 2008.
South Africa is largely reliant on coal for energy, with nuclear energy contributing just six percent to the overall energy supply. However, there are a number of problems with using coal as an energy source.
* It is not sustainable and coal reserves will eventually dry up.
* It is very bad for the environment, with the carbon dioxide produced by coal contributing significantly to the greenhouse effect.
* Logistically it is impractical as the country’s main coal reserves are in the north-east while the bulk of the electricity load is near the coast (Cape Town, Durban).
In an attempt to find feasible alternative energy sources (solar energy and wind energy are also being considered but are regarded as being experimental), the government has turned once more to nuclear energy.
South Africa has two nuclear reactors, which are housed at Koeberg and each produce 900 MWe. The use of nuclear energy is controversial for two reasons. The first is that it is extremely volatile and a meltdown will mean the annihilation of the surrounding population (think Chernobyl) and radioactive poisoning of the earth. The second is that the creation of nuclear energy results in radioactive waste which cannot be safely reabsorbed by the earth.
The government has been investigating the possibility of PBMRs since 1993. They have commissioned a pilot project demonstration plant which is set to be completed by 2011. If this project is a success, the first commercial PBMRs are planned for 2013.
Each PBMR will produce 165 MWe. Eventually the government plans to have 24 or more PBMRs which will produce at least 4000 MWe, amounting to a quarter of South Africa’s electricity supply.
What is a PBMR?
A PBMR is a helium-cooled High Temperature Reactor. Other countries, such as Germany, Japan and China, are also developing gas-cooled HTRs, but the South African PBMR is generally regarded as the leader in this technology.
A PBMR is most simply described as a huge graphite cylinder (6.2m in diameter and 27m high), which is full of uranium enriched, graphite encased pebbles (456 000 fuel pebbles). There is a graphite column in the centre of the core and the pebbles are in the area around it.
The pebbles
Particles of enriched uranium dioxide are coated with silicon carbide and pyrolitic carbon (to make them safer) and then encased in graphite. The fuel pebbles resemble graphite tennis balls.
The coolant
Helium is used as a coolant and to drive the closed cycle gas turbine and generator. The coolant enters the top of the vessel at 500 degrees Celsius and once it has cooled the nuclear reaction, it leaves the bottom of the vessel at 900 degrees Celsius. The gas passes through a turbine which drives the electricity generator.
The process
The reactor is continuously replenished with ‘fresh’ pebbles as ‘used’ pebbles are removed from the bottom. After each pebble passes through the reactor, it is measured to ascertain how much ‘fissionable material’ is left. It takes a pebble about six months to travel through the reactor and each pebble contains enough ‘fissionable material’ to pass through the reactor six times, making the ‘life’ of a pebble six years.
Once the pebble is spent it will be stored in an onsite storage facility. This facility is made up of ten tanks which can each store 600 000 pebbles.


Pebble-Bed Reactor: a paper delivered at World Nuclear Association Symposium, 2003
How do they compare to traditional reactors?
Most importantly, PBMRs are safer than traditional reactors. When it comes to nuclear reactors, meltdowns generally occur when there is too much heat. In a traditional reactor, there is an ‘active’ cooling system. If the mechanics (such as the pumps) of the system fail, then the heat in the reactor escalates causing an increase in the amount of energy released. This eventually damages the nuclear fuel and results in a radioactive explosion.
The PBMR on the other hand, has a ‘passive’ cooling system. The core structure is created in such a way that the heat produced by the nuclear fission is less than the heat lost through the core surface. This means that the reactor will never reach a temperature where the fuel will become damaged. Further safety measures have been put in place so that if the plant malfunctions, the reactor will stop any nuclear fission and cool itself down.
Another advantage of PBMRs is that they are more efficient than conventional reactors because the helium coolant also acts as an energy transfer medium. In other reactors the coolant gas is used to heat steam which in turn drives the turbines. Cutting out this step makes the reactor more efficient and it also means that the plant does not need to be located near large supplies of water.
The modular nature of the PBMR means that they can be set up anywhere. They are also far more efficient when it comes to space — a plant can be set up on a plot the size of a soccer field.
PBMRs are also supposed to be more environmentally friendly because the radioactive material is already encased in silicon carbide and graphite which decreases the possibility of the waste contaminating the environment.
Voices of dissent
While this picture of PBMRs seems to be rather rosy, not everyone is extolling the benefits of more nuclear power. The environmental group Earthlife objects strongly to the prospect of South Africa expanding their nuclear programme.
Firstly, they assert that the claim that PBMRs are safe is not entirely true. According to a member of the US Nuclear Regulatory Commission, the design of the PBMR is flawed because the unpredictable movements of the pebbles within the reactor lead to the possibility of core instability. Furthermore, they claim that there is no ‘safe’ dose of radiation and that by having nuclear plants, the public (and more specifically the workers) is being exposed to harmful radiation.
Their second qualm is that there is no way to dispose of radioactive waste — a problem which will only increase with the proliferation of nuclear energy. The Kyoto Protocol doesn’t recognise nuclear energy as a clean alternative to fossil fuel, which they say suggests that claims that nuclear power is ‘cleaner’ than coal power are unsubstantiated.
Earthlife proposes that renewable energy sources such as wind, solar and ocean sources are feasible and cost effective alternatives to nuclear power. Although they will only be able to provide 13 percent of the electricity demand by 2020, studies have found that they should be able to supply at least 70 percent by 2050.
Allegedly, the PBMR programme has already cost R2-billion and is expected to cost another R11.3-biliion. Earthlife claims that renewable energy will be cheaper and will create 27 times as many jobs. The government however argues that because the objective is to start a ‘power stations construction industry’, the PBMRs hold great promise in terms of job creation.
Essentially, the whole debate comes down to a matter of expense. Do the benefits outweigh the costs? Unfortunately, in the case of nuclear power, expense is a relative term which depends very much on what you regard as valuable.
See also:
Pro Pebble-Bed Reactors
Con Pebble-Bed Reactors

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Bjorn Carey, Popular Science, October 15, 2006

The first reactor-on-a-barge will bring power to Russia’s electricity-starved Arctic Photo: Bob Sauls
While the U.S. hems and haws over reviving nuclear energy as a less expensive alternative to oil, Russia has dug back 30 years in our nuclear history to find a solution for some of its own energy woes: the floating nuclear power plant.
The Russian nuclear-energy company Rosenergoatom is planning a mobile plant to deliver electricity to hard-to-reach northern territories near the White Sea, where harsh weather makes regular coal and oil fuel deliveries unreliable and expensive. The $200-million floating plant—slated for construction next year—could provide relatively inexpensive, reliable electricity to 200,000 people.

Graphic: Paul Wootton
Although the concept of a water-borne nuke plant might sound outlandish, it isn’t new, nor did it originate in Russia. Westinghouse Electric Company considered the idea in the 1970s and built an immense dry-dock facility in Jacksonville, Florida, where plants would be launched and floated north along the Eastern Seaboard, conveniently doling out power to towns in need. Engineers would be able to standardize construction for multiple plants in an offsite factory with increased quality control and reduced production costs before tugging a plant to its port of call. But ultimately, says retired Westinghouse consultant Richard Orr, energy conservation following the 1973 OPEC oil embargo killed the project.
The Russian plan is to mount two reactors on a football-field-size barge, float it to a port, connect power lines to the mainland, and turn on the reactors, providing communities with affordable electricity. The plant will store waste and spent fuel in an onboard facility that workers will empty every 10 to 12 years during regular maintenance overhauls. After 40 years, the normal life span for a nuclear plant, the decommissioned plant would be towed away and replaced with a new one. The reactor and spent fuel would go to a storage facility, but the barge could be recycled.
Yet because the safety of the Russian facility is still unknown, the prospect of resurrecting the Westinghouse idea in the White Sea has drawn protest from environmental groups such as Greenpeace and the Norwegian foundation Bellona. One concern is that a boat could ram the plant and spill waste into the water. An even bigger fear is that a nasty storm could cut the plant off from the land-based power supply required to run plant operations. Should emergency generators fail, says David Lochbaum, director of the Nuclear Safety Project at the Union of Concerned Scientists, a Chernobyl-like disaster could ensue. In a worst-case scenario, an overheated core could melt through the bottom of the barge and drop into the water, creating a radioactive steam explosion. Such a cloud could do far more damage than the plume of nuclear fallout kicked up by the 1986 explosion of the Chernobyl nuclear power plant in the former U.S.S.R., Lochbaum notes, because the human body absorbs radioactive water droplets more easily than it does radioactive ash. “Its worst day would be much worse than a land power plant’s,” he says.
Sergey Obozov, acting director for Rosenergoatom, says that reactors at sea have a proven safety record: The facility would be powered by two 60-megawatt KLT-40S reactors adapted from those already in use on three Russian nuclear-powered icebreakers. Yet Cristina Chuen, a Russian nuclear-energy specialist with the Monterey Institute for International Studies in California, cautions that subtle performance differences might arise when running the reactor for pure energy generation instead of propulsion, noting that the cooling system remains unproven. Although the technology exists to contain a burning core, Rosenergoatom won’t say if the plant — which was designed a decade ago — will include the most modern safety measures.
With a building permit in hand, Rosenergoatom aims to have the facility afloat in the port city of Severodvinsk in the southeastern White Sea by late 2010. “The Russians have learned a lot about safety from the U.S. Department of Energy, Sweden and Norway — who probably all wish [the Russians] would focus on things other than a floating nuclear power plant,” says Chuen, who adds that she wishes the planning process were more transparent. “Maybe it will turn out great, but I just hope they did all the research to make sure it’s safe.”

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Roland Piquepaille, ZDNet, October 15, 2006
In A Floating Chernobyl?, Popular Science reports that two Russian companies plan to build the world’s first floating nuclear power plant to deliver cheap electricity to northern territories. The construction should start next year for a deployment in 2010. The huge barge will be home for two 60-megawatt nuclear reactors which will work until 2050… if everything works fine. It looks like a frightening idea, don’t you think?
Here are some details provided by Popular Science.
The Russian nuclear-energy company Rosenergoatom is planning a mobile plant to deliver electricity to hard-to-reach northern territories near the White Sea, where harsh weather makes regular coal and oil fuel deliveries unreliable and expensive. The $200-million floating plant — slated for construction next year — could provide relatively inexpensive, reliable electricity to 200,000 people.
In fact, the state-owned nuclear power monopoly Rosenergoatom will team with the Sevmash shipyard in the Arctic port of Severodvinsk to build this floating nuclear power plant.
But what will it look like? The image of this floating nuclear plant provided by Popular Science is really neat, but other sources show that this barge will maybe not look as nice. Here is a first example shown by euroarctic.com in “Controversial nuclear plant under construction” (March 14, 2006) and by MosNews.com in “First Contract to Build Floating Nuclear Power Plant Signed in Russia” (June 14, 2006).

Russian floating nuclear plant
You also can read the first paragraph of an article of POWER Magazine published in August 2006, “Russia’s new nuclear navy.” Below is a digital artist’s conception of this world’s first floating nuclear power plant. (Credit: Sevmash)

Another artist’s impression
Let’s now return to Popular Science for more facts about this project.
The Russian plan is to mount two reactors on a football-field-size barge, float it to a port, connect power lines to the mainland, and turn on the reactors, providing communities with affordable electricity. The plant will store waste and spent fuel in an onboard facility that workers will empty every 10 to 12 years during regular maintenance overhauls. After 40 years, the normal life span for a nuclear plant, the decommissioned plant would be towed away and replaced with a new one.
Of course, this might work as forecasted. But the risks are very high. For example, such a floating plant could spill waste into the White Sea. But even more frightening, what will happen if the nuclear reactors melt into the water? Well, we’ll see a radioactive steam explosion. And I wouldn’t like to be close to such an explosion…
For more information, you also should read a long paper available on the Green Cross Switzerland website, “Floating Nuclear Power Plants in Russia” (PDF format, 85 pages, 0.99 MB), published in 2004.

Sources: Bjorn Carey, Popular Science, October 2006; and various websites

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