New insights in accelerator-driven systems
As part of EUCARD2 activities, and co-sponsored by EPS Technology and Innovation Group (TIG), a workshop [1] on the status of new developments in Accelerator-Driven Systems or ADS was held at CERN on February 7-9. Entitled “Status of Accelerator Driven Systems Research and Technology Development”, the scope of the workshop was to review the current state of the art of ADS programmes and address in particular subjects like:
• Critical aspects for accelerator operation
• Accelerator-target interface challenges
• Status of major ADS programmes in the world
• ADS coupling experiments
• Social and economic perspective of ADS
• Lessons learned and future R&D.
A dedicated session was innovative ideas and new R&D, chaired by TIG.
The basic idea in ADS – sub-critical assemblies driven by high power accelerators through a spallation target coupled to the reactor core – date back to the late 1980’s and early 1990’s. Although no complete demonstration facility has been built as yet, R&D is gaining momentum with governments’ declared commitments to finance R&D and construction costs in Europe (Belgium), China and India notably.
In the technical presentations, it became apparent that the ADS roadmap still faces important technological challenges with regard to the accelerator, the target, the sub-critical reactor and new types of safety issues. The development of accelerators advances well, with beam powers of up to 10 MW for cyclotrons and 100 MW for linacs now looking to be feasible. However long-term high-reliability operation of the front-end system and main accelerator still requires demonstration. Further progress is required with respect to beam loss and especially beam trip management, to avoid fast temperature and mechanical stress transients in the reactor. Beam delivery and raster systems have been demonstrated and are in operation, but various problems related to the accelerator-reactor coupling have still to be investigated.
Special attention has to be given to the target and especially the beam-window, as these parts are subjected to complex stress, corrosion and irradiation conditions which are not encountered in normal reactors. In particular prototype and test components should be developed for > 10 MW target systems. Lifetimes of the proposed materials should be tested in the radiation, thermal, and chemical environments anticipated: understanding the behaviour of fuel and structural materials in complex and aggressive environments is a crucial R&D activity and systematic material irradiation tests should be undertaken in existing and new facilities. These will have a significant influence on design evaluations relative to system life, requirements for maintaining or replacing equipment, licensing, and life-cycle costs. On top of this, the primary and secondary proton damage to these fuel and structural materials in an ADS is an additional and essentially new domain that has only limited resemblance to the proton damage experienced in existing spallation targets. New equipment and components must be designed and tested to assure lifetime reliability and availability.
The proposal to use relatively new type of coolants (lead, LBE or gas), especially in combination with new fuel types and cladding materials, demands specific attention to the thermal-hydraulics and core mechanics in normal operational regime and accident conditions, with studies of the compatibility between these coolant/material combinations and of the role played by corrosion mechanisms.
New techniques and tools must be developed to control the coolant chemistry, the sub-criticality level monitoring, the coupling between power level and accelerator beam power, as well as control feedback systems to increase the reliability of the accelerator.
Another point to be raised is the growing importance of international collaborations and the role of international bodies. Given the level of investment necessary to build the required infrastructure for an ADS facility, more and more R&D efforts are performed at international level, through either bilateral research agreements or collaborative projects, like those organized by the European Commission in its framework programmes. Global cooperation will however require additional efforts of convergence in goals and utilization purposes, hence the role that will need to be played by international bodies, such as the IAEA, ISTC and NEA, in bringing together different players around the world that are involved in the same research areas, as well as in sharing and disseminating relevant information.
The workshop attracted 73 participants from all around the world, with a nice mixture of laboratories, universities, funding agencies and industry.
