ThorEA - Towards an Alternative Nuclear Future.pdf

Frequently Asked Questions continued
Q8. ThorEA has suggested an ADSR core with a criticality factor of 0.985, but that optimal ADSR core design calculations
may favour higher core criticalities and hence lower beam currents, relaxing somewhat the design parameters of the
proton accelerator. Why not go to higher criticality factors, and perhaps greatly simplify the accelerator design?
A8. ThorEA’s initial choice of criticality coefficient is based upon how far below k=1 it is feasible to go yet still be able exploit
currently realisable accelerator technologies. A total proton beam power of 10MW is close to the current state of the art
and therefore is an entirely appropriate starting point to maximise the flexibility in the criticality whilst increasing safety
margins. It should also be noted that the report indicates that it may be desirable to deliver the total driver power using
several accelerators simultaneously. This will also facilitate a simplification of the design of each individual accelerator,
albeit at the expense of complexity in beam delivery. This latter point has already been addressed by IPR lodged by STFC
and members of ThorEA.
Q9. ThorEA suggests higher currents are, broadly speaking, easier to achieve than higher energies. Doesn’t this conflict
with the opinion of the ESS, which is updating its parameters from the 2003 design to decrease the current and raise
the energy by a factor of about 2.5, going to 2.5 GeV? Lower currents can enable higher reliability.
A9. For a given accelerator power there is always a trade-off between current and energy, depending upon the particular
accelerator technology employed. For some systems, at mA currents, it may well prove to be easier to double the beam
power by doubling the beam energy. However, the statements about ESS are erroneous. Whilst the concept of the ESS
driver energy increasing from 1.3 to >2GeV has been discussed (as it must) any decision on beam delivery parameters will
be based not upon arguments of a trade-off between current and energy, but entirely upon the neutronic performance of
the ESS neutron spectrometers themselves. Indeed our own calculations on the ESS target, performed for and funded by
the EU-FP7 ESS Preparatory Phase Project, show that increasing the proton energy substantially increases the neutron
density distribution within the target, with a potentially deleterious effect on neutron delivery to the moderators and
subsequently the beam lines. Professor Colin Carlile, the Director of the ESS project has confirmed to ThorEA that no
decisions have yet been made to take the ESS driver to energies above the 2003 value of 1.3GeV.
Q10. FFAG R&D is still at an early stage, and FFAGs indeed deserve further support and exploration, but this direction
is high risk, high gain. Is there not a significant probability that FFAGs will not be “more reliable, cheaper and
more compact”?
A10. There is a significant risk that FFAGs may not appropriate for ADSR systems integration – but that is why a major R&D
programme is proposed by ThorEA, and why other more conventional technologies will be evaluated alongside the ns-FFAG
option. We also intend to discover whether FFAG will be more reliable, cheaper and more compact, noting that there have
already been significant advances in FFAG technology over the last 12 months, particular when compared to the rather
slow rate of development of competitor technologies.
Whilst it is clear that all ADSR technologies present major challenges, it is also widely accepted that thorium fuelled
ADSR systems could afford a significant and timely solution to some of our energy needs. Therefore if existing accelerator
systems were capable of delivering ADSR technology there is no doubt that they would already be doing so. It is in this
context that we believe major investment at this stage of development could have major technological and socioeconomic
impact for the UK.
68 Towards an Alternative Nuclear Future