Carlo Ceballos obtains PhD on shorter life-span of radioactive waste
05 February 2007 by TNWToday | M&CThe Accelerator Driven Subcritical Reactor (ADSR) offers a great advantage over conventional nuclear reactors. The ADSR can use long-lasting nuclear waste as nuclear fuel and convert it into waste that remains dangerous for a much shorter period of time. However, there are still major financial and technological problems associated with the ADSR. On Monday, February 5, Carlos Ceballos received his TU Delft PhD degree based on this research subject.
The nuclear reactor that TU Delft researcher Carlos Ceballos studied is based on the work of Italian Nobel Prize winner Carlo Rubbia. In 1995, Rubbia made a strong case for the development of a reactor that can convert radioactive waste from other nuclear power plants into waste that remains dangerous for much shorter periods of time – only for 100 to 150 years.
Ceballos, who is from Colombia, primarily focused on the safety considerations for this type of reactor. The Accelerator Driven Subcritical Reactor (ADSR) is not a normal ''critical'' reactor, like conventional nuclear reactors. In conventional reactors, a natural chain reaction is maintained by establishing an equilibrium between the release of neutrons through the fission of uranium nuclei and their absorption elsewhere.
In the ‘subcritical’ ADSR, the number of free neutrons produced is not enough to maintain a chain reaction. An external particle accelerator supplies the extra neutrons that are needed to maintain this process in the reactor. When a potentially dangerous situation arises, the ADSR''s particle accelerator is shut down and the number of neutrons - and thus the potential danger - quickly diminishes. Ceballos''s reactor is cooled by a liquid mixture of lead and bismuth. The use of natural circulation means that no pumps are required, so the cooling system is very safe. This mixture of metals is moreover extremely insensitive to oxygen or water.
Ceballos used a computer to simulate the processes occurring in the reactor. "In my research, the subcritical reactor remained a safe concept, even during incidents," he concluded.
The research has moreover clearly shown that the reliability of the accelerator, which is needed to provide the missing neutrons, is of crucial importance. However, because the current generation of accelerators malfunction so often, the key components of such reactors can be damaged as a result.
In addition to the technological problems, there are also still huge financial obstacles to overcome before the ADSR can be used in practice and contribute to reducing the length of time that nuclear waste remains dangerous. This involves expensive technology. "The reactor will only be developed if governments around the world take action," Ceballos said in an interview in Delta, TU Delft''s university newspaper.
See also Delta 23 17-08-2006 (in Dutch)
