Editing Subcritical reactor (section)

== Technical challenges ==
There are technical difficulties to overcome before ADS can become economical and eventually be integrated into future nuclear waste management. The accelerator must provide a high intensity and also be highly reliable - each outage of the accelerator in addition to causing a [[scram]] will put the system under immense [[thermal stress]]. There are concerns about the window separating the protons from the spallation target, which is expected to be exposed to stress under extreme conditions. However, recent experience with the MEGAPIE liquid metal neutron spallation source tested at the [[Paul Scherrer Institute]] has demonstrated a working beam window under a 0.78 MW intense proton beam. The chemical separation of the transuranic elements and the fuel manufacturing, as well as the structure materials, are important issues. Finally, the lack of [[nuclear data]] at high neutron energies limits the efficiency of the design. This latter issue can be overcome by introducing a [[neutron moderator]] between the neutron source and the fuel, but this can lead to increased leakage as the moderator will also scatter neutrons ''away'' from the fuel. Changing the geometry of the reactor can reduce but never eliminate leakage. Leaking neutrons are also of concern due to the [[activation product]]s they produce and due to the physical damage to materials neutron irradiation can cause. Furthermore, there are certain advantages to the fast neutron spectrum which cannot be achieved with [[thermal neutron]]s as are the result of a moderator. On the other hand, thermal neutron reactors are the most common and well understood type of nuclear reactor and thermal neutrons also have advantages over fast neutrons.

Some laboratory experiments and many theoretical studies have demonstrated the theoretical possibility of such a plant. [[Carlo Rubbia]], a nuclear [[physicist]], Nobel laureate, and former director of [[CERN]], was one of the first to conceive a design of a subcritical reactor, the so-called "[[energy amplifier]]". In 2005, several large-scale projects are going on in Europe and Japan to further develop subcritical reactor technology. In 2012 CERN scientists and engineers launched the [[International Thorium Energy Committee]] (iThEC),<ref>{{Cite web | url=http://www.ithec.org |title = IThec &#124; Un site utilisant WordPress}}</ref> an organization dedicated to pursuing this goal and which organized the ThEC13<ref>{{Cite web | url=http://indico.cern.ch/event/222140/timetable/#20131027 | title=* Thorium Energy Conference 2013 (ThEC13) * CERN Globe of Science and Innovation, Geneva, Switzerland}}</ref> conference on the subject.