  Graphite-moderated nuclear reactors have already produced more than 250000
tons of irradiated nuclear graphite, or i-graphite, world-wide. The
sustainability of this technology relies on the end-of-life management of its
moderator, which is activated into a long-lived nuclear waste, by neutron
fluxes, during operating time. In particular, C14 is created. Nuclear
transmutation, enabled by laser-driven particle acceleration, has been
envisioned as a potential novel treatment scheme for long-lived nuclear waste.
By triggering controlled nuclear reactions with energetic particles, long-lived
radionuclides could be transformed into stable isotopes. Such a system could
treat the C14 nuclei trapped within the i-graphite matrix, which is difficult
to isolate by other means. This work performs a quantitative preliminary study
of this transmutation scheme, in order to assess its feasibility at an
industrial scale. The method used can be transposed to assess any transmutation
scheme using a beam of particles directly sent on the material to be treated.
First, a nuclear interaction channel which transmutes C14 nuclei without
creating new long-lived radionuclides is identified. It consists in the choice
of a type of particle, among which protons, gamma photons and neutrons can all
be accelerated by laser-matter interaction; and it is completed by the adequate
energy at which this particle must be sent on i-graphite. To that end, the
nuclear cross-sections of C12, C13 and C14 are reviewed, neglecting other
impurities in i-graphite. Then, based on the interaction channel
identification, the energy cost of this scheme is estimated. Protons between 1
and 5 MeV make it possible to transmute C14 without creating any new long-lived
activity. However, our result show that, even in this favorable reaction
channel, the transmutation energy cost is too high for an i-graphite
transmutation scheme to be feasible.
