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>A Nuclear Third Way

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By Lord Julian Hunt, a former fusion technology researcher and a visiting professor at Delft University of Technology in the Netherlands and Graham O’Connor, a former senior scientist at the ITER (International Thermonuclear Experimental Reactor) project in France (THE NEW YORK TIMES, 25/03/11):
The Fukushima disaster has inevitably prompted concern in many countries about nuclear power. But are the correct questions being asked?
A danger in the debate is that nuclear is often portrayed as a single, undifferentiated energy source. This is not only wrong, but also risks losing the opportunity we have to debate the role that new technologies — not only of fusion and fission, but also hybrid methods — can play in the energy mix in the 21st century.
Indeed, those who seek to write nuclear off completely are missing what could be extraordinary, breakthrough developments on the horizon with hybrid technologies that might — relatively shortly — completely reshape the way we think about nuclear energy.
The starting point for debate, for friends and foe of nuclear alike, should be the daunting energy problems many governments face. With growing challenges to energy security, the range of energy sources must be broadened, with greenhouse gas emissions reduced because of global warming. There is also a pressing need to reduce air, water and land pollution by coal and oil extraction and combustion (which continue to cause more deaths per year than nuclear power has in its entire history).
Renewables are a key part of the solution, but no country can be sure of the reliability of energies such as wind or solar in 20 to 50 years, given changed climatic conditions. Relying on neighboring countries for power also carries risks.
There seems to be no alternative but to include nuclear in the energy mix for at least decades to come. So, what do new generations of fission, fusion and hybrid offer?
• Fission
Modern power stations using fission, which harnesses energy from the radioactive decay of uranium and other fissile materials, are considerably safer than older ones such as Fukushima — constructed 30-40 years ago. This is because of stronger containment structures, more secure storage of spent fuel rods and emergency systems to prevent overheating. Further developments over the next 20 years will also reduce volumes of radioactive waste.
Because the supply of uranium may be limited, there are longer-term, controversial plans in some countries to construct “fast breeder” reactors to recycle waste and use the fuel more efficiently. However, there are proliferation dangers associated with the plutonium byproduct.
Fission will only continue to be acceptable if the immediate risks of the current and planned systems are reduced. Despite improved safety, the rare, but catastrophic failures of technological and human operations such as Chernobyl cannot be dismissed. As Fukushima showed, there are also remaining risks from earthquakes, tsunamis, severe storms and even aircraft crashes — plus the dangers of fission associated with the storage of waste for over 10,000 years in geological repositories.
• Fusion
The principle of controlled thermonuclear fusion is to extract energy from processes similar to those occurring inside the Sun, where hydrogen atoms are fused together to form helium. This is a “clean” process with negligible long-lived radioactive waste.
However, because of the great size needed for a “pure” fusion reactor and the unsolved problem of fabricating materials to withstand the heat, the development challenges are substantial and may take decades to overcome.
• Hybrid
The long-term future of nuclear may lie with a still-little-known third option: combining nuclear fission (atoms splitting) and fusion (atoms merging) in a single “hybrid” reactor. Indeed, without publicity, governments, agencies and research institutes are already moving tentatively in this direction.
Hybrid fusion was first proposed by the American Nobel laureate Hans Bethe to enable more widely available reserves of nuclear fuels other than uranium, such as thorium, to be used. Hybrid could become a reality within the next two decades — the Institute of Plasma Physics in China is planning to build a proof-of-principle prototype experiment by 2025.
The basic principle is that neutrons generated by fusion in the plasma core stimulate fission in the outer “blanket” that contains uranium or other fissile materials (which could include nuclear waste). Because there is relatively less energy extracted from the plasma than in pure fusion, continuous operation can be engineered more readily.
The fission is well below critical mass and only operates when there is a current flowing in the plasma. This is why the system is safer.
The technology of maintaining the hybrid reactors has many advantages, and it uses a wider range of fuels. They do not produce the long-lived waste produced in fission because the high-energy neutron flux from the fusion process “transmutates” these into isotopes that decay over a hundred rather than tens of thousands of years.
Not only does this eliminate some nuclear waste problems; it helps to rid the world of plutonium and other weapons-grade materials. Furthermore, if thorium is used, it cannot be converted into weapons-grade uranium.
While even modest-sized hybrid reactors could provide affordable and almost limitless energy, their power output can be controlled through the fusion process. Thus the operation is safe enough for a power station to be located even in countries prone to natural hazards.
Furthermore, the controllability would allow fusion-fission power to be used either as base load or more flexibly in combination with renewable energy, which is inherently more variable.
Many aspects of hybrid nuclear require further intense research — and economic analysis. Current collaboration between groups in Russia, China, the United States, South Korea and Britain needs to involve more countries.
While workable hybrid technology is still some way off, timeframes could be accelerated with the right commitments from the public and private sector.
This “third nuclear way” deserves much wider understanding and support from governments, scientists, engineers and environmentalists alike if we are going to have the maturity of debate we so badly need about the role that nuclear can play in the energy mix over decades to come.
Fuente: Bitácora Almendrón. Tribuna Libre © Miguel Moliné Escalona

marzo 28, 2011 - Posted by | energía

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