Prospects for nuclear waste transmutation using high flux subcritical reactors

A design concept and characteristics for a high flux subcritical reactor (HFSR) are presented. By replacing the control rods with photoneutron generators, we could improve safety and perform radioactive waste burning in subcritical reactors that have primary system size, power density and cost comparable to a pressurized water reactor (PWR). The initial design is based on a small PWR, dry fuel cycle, intense resonance neutron source and power monitoring system with in-core gamma-ray detectors, now under development in the US, Korea, Russia and Ukraine. An important aspect of the HFSR is the reactor's modular design. To increase neutron source intensity the module is divided into two zones: a booster with fission electric cells (FEC) and a blanket with spent/depleted fuel. The FEC is essentially a high-voltage power source that directly converts the kinetic energy of the fission fragments into electrical potential of about 2 MV. A neutron gate (absorber and moderator) imposed between two subcritical zones permits fast neutrons from the booster flow to the blanket. Neutrons moving in the reverse direction are moderated and absorbed. However, these in-core applications require somewhat smaller high-brightness neutron generators that are presently available. An inexpensive method of obtaining large neutron fluxes is target-distributed electron accelerators (TDA), in which a FEC electrical field compensates for lost beam energy in the thin photon production targets. Neutrons are mostly generated in the booster surrounded the targets. The charge deposited by the electron beam in the target could be used to suppress the flow of secondary electrons across the gap between the FEC electrodes. (author)