Idaho National Laboratory (INL) scientists have set a new world record with next-generation particle fuel for use in high temperature gas reactors (HTGRs).

The fuel pellets contain a kernel of enriched uranium surrounded by carbon and carbide layers that act as a containment boundry for the radioactive material. (Credit: Image courtesy of DOE/Idaho National Laboratory)

The Advanced Gas Reactor (AGR) Fuel Program, initiated by the Department of Energy in 2002, used INL’s unique Advanced Test Reactor (ATR) in a nearly three-year experiment to subject more than 300,000 nuclear fuel particles to an intense neutron field and temperatures around 1,250 degrees Celsius.

INL researchers say the fuel experiment set the record for particle fuel by consuming approximately 19 percent of its low-enriched uranium — more than double the previous record set by similar experiments run by German scientists in the 1980s and more than three times that achieved by current light water reactor (LWR) fuel. Additionally, none of the fuel particles experienced failure since entering the extreme neutron irradiation test environment of the ATR in December 2006.

“This level of performance is a major accomplishment,” said Dr. David Petti, Director of the Very High Temperature Reactor Technology Development Office at the U.S. Department of Energy’s INL. The purpose of the fuel program is to develop this particle fuel, produce experimental data that demonstrates to the Nuclear Regulatory Commission that the fuel is robust and safe, and re-establish a U.S. fuel manufacturing capability for high temperature gas reactors. INL has been working with Babcock and Wilcox Inc., General Atomics and Oak Ridge National Laboratory (ORNL) to establish standards and procedures for the manufacture of commercial-scale HTGR fuel. The overarching goal of the AGR Fuel Program is to qualify coated nuclear fuel particles for use in HTGRs such as the Next Generation Nuclear Plant (NGNP). Developing particle fuel capable of achieving very high burnup levels will also reduce the amount of used fuel that is generated by HTGRs.

“An important part of our mission is the development and exploration of advanced nuclear science and technology,” said Dr. Warren F. “Pete” Miller, assistant secretary for Nuclear Energy. “This achievement is an important step as we work to enable the next generation of reactors, decrease fossil fuel use in industrial applications, make fuel cycles more sustainable, and reduce proliferation risks.”

“AGR-1″ is the first of eight similar experiments which aim to confirm designs and fabrication processes and performance characteristics for such fuel. Future AGR fuel tests will include particle fuel produced on a prototypic industrial scale to further prove the irradiation performance of the NGNP-specific fuel design. The 18-foot-long AGR-1 experiment was inserted in INL’s ATR core and allowed for each of six capsules containing the particle fuel specimens to be monitored and controlled separately. Inside the ATR core, the fuel specimens were subjected to neutron irradiation many times higher than what they would experience inside an HTGR or a current light water reactor, allowing INL researchers to gain irradiation performance data for nuclear fuel and materials in a shorter time. The team is monitoring the AGR fuel for a number of factors including “burn-up,” which is a measurement of the percent of uranium fuel that has undergone fission reactions.

Although the experiment has now left the ATR, researchers still have more work to do before the AGR-1 test campaign will be finished. Post irradiation examination (PIE) will begin at INL and ORNL facilities and allow scientists to examine the fuel up close so that the fuel and its layers of coatings can be evaluated for degradation patterns and other characteristics. In addition, controlled higher temperature testing in furnaces is planned to determine the safety performance of the fuel under postulated accident conditions. These activities will last another two years.

The Next Generation Nuclear Plant Program aims to use a high temperature gas reactor to produce high temperature process heat and hydrogen used by many industrial facilities in daily operations and to support the broader goal of developing the next generation of nuclear power systems that provide abundant carbon-free electricity on a 24/7 basis. Excellent fuel irradiation performance must be demonstrated before high temperature gas reactors can be licensed and co-located with these complementary industrial facilities. Reaching this world record peak burn-up of 19 percent without any particle failure demonstrates the robustness of this particle fuel design.

Six months is all it took to flip Europe’s climate from warm and sunny into the last ice age, researchers have found.

They have discovered that the northern hemisphere was plunged into a big freeze 12,800 years ago by a sudden slowdown of the Gulf Stream that allowed ice to spread hundreds of miles southwards from the Arctic.

Previous research had suggested the change might have taken place over a longer period — perhaps about 10 years.

The new description, reminiscent of the Hollywood blockbuster The Day After Tomorrow, emerged from one of the most painstaking studies of past climate changes yet attempted.

“It would have been very sudden for those alive at the time,” said William Patterson, a geological sciences professor at the University of Saskatchewan in Saskatoon, Canada, who carried out the research. “It would be the equivalent of taking Britain and moving it to the Arctic over the space of a few months.”

His findings, published at a recent conference, reinforce a series of studies suggesting that the earth’s climate is highly unstable and can flip between warm and cold very rapidly with the right trigger.

Most such research is based on analysing cores drilled from ice or from the sediment found at the bottom of oceans or lakes. In such cores the ice or sediment is found in layers whose composition shows what the climate was like at the time they were laid down.

Ice cores drilled from the Greenland ice cap have already shown that the big freeze of 12,800 years ago — known as the Younger Dryas mini-ice age — happened fast but lacked the detail to pin it down precisely.

Patterson, however, obtained mud deposits from Lough Monreagh, a lake in western Ireland, a region he says has “the best mud in the world in scientific terms”.

Patterson used a precision robotic scalpel to scrape off layers of mud just 0.5mm thick.Each layer represented three months of sediment deposition, so variations between them could be used to measure changes in temperature over very short periods.

Patterson found that temperatures had plummeted, with the lake’s plants and animals rapidly dying over just a few months. The subsequent mini-ice age lasted for 1,300 years.

What caused such a dramatic event? The most likely trigger is the sudden emptying of Lake Agassiz, an inland sea that once covered a swathe of northern Canada.

It is thought to have burst its banks, pouring freezing freshwater into the North Atlantic and Arctic oceans, disrupting the Gulf Stream, whose flows depend on variations in temperature and salinity.

A single year’s disruption in the Gulf Stream could have been enough, said Patterson, to let ice grow far to the south of where it usually formed. Once it had taken over, the Gulf Stream was unable to regain its normal route and the cold took hold for about 1,300 years.

Some scientists have suggested that if the Greenland ice cap melts it could have a similarly dramatic effect by disrupting the world’s ocean currents.

Other research has shown that rapid climate flips are normal. In its 4.5-billion-year history, the earth has experienced at least four main ice ages, of which the last, the Quaternary, is still continuing.

Within each ice age, however, there are periods when ice advances or retreats, and in the past 60,000 years alone the earth is thought to have warmed or cooled by up to 7C at least 20 times. The current interglacial period has lasted about 10,000 years.

“Human civilisation has grown up in a period of remarkable climatic stability,” said Tim Lenton, professor of earth system sciences at the University of East Anglia.

“In the period from 65,000 to 10,000 years ago there were periods of abrupt warming and cooling roughly every 1,500 years, when the temperature in Greenland might fall or rise by 10C in a decade.”

Patterson’s findings are supported by the research of Chris Stringer, professor of human origins at the Natural History Museum in London.

He believes the extinction of Neanderthals roughly 30,000 years ago was linked to a series of rapid climate fluctuations that began more than 40,000 years ago. He said: “Climate is basically unstable, so one of the mysteries is why it has stayed warm for the last 10,000 years.

“Some researchers have suggested this may be linked to the activities of early humans, who started growing crops and clearing forests 8,000 years ago.

“That may have put enough greenhouse gases into the air to stave off another ice age, but the problem now is that we have gone too far the other way.

“The amount of greenhouse gases in the air is greater than at any time in the last million years, so ironically, the threat now is from global warming.”

Patterson is still focusing his efforts on the past. He has built a new robot capable of shaving tiny slivers from the shells of fossilised clams, showing temperature almost day by day from millions of years ago.