Driven Subcritical Fission Research Reactor Using a Cylindrical Inertial Electrostatic Confinement Neutron Source

An accelerator-driven sub-critical reactor potentially offers important safety advantages for future fission power systems. A fast neutron spectrum sub-critical reactor system with heavy metal coolant has received considerable attention in Europe and in the US and Japan. Alternate versions, using intermediate or thermal spectrum neutronics with lighter moderators are also possible. Another attractive application of a driven reactor is for burning of plutonium isotopes, actinides and select long-lived fission products. In addition to large power reactors, special low power designs are candidates for student subcritical laboratory experiments and research reactors. The driven system is especially beneficial since the enhanced safety allows a wider variety of experimental conditions, including dynamic studies. The main approach considered for the driver to date has been an accelerator, spallation-target system. While this concept appears to be feasible, the large size and cost of the accelerator system remain an issue. Also, the in-core target system poses significant design and engineering complications. Here we consider the alternative of using a unique inertial electrostatic confinement (IEC) neutron sources which are small enough to fit within fuel element channels or in a central cavity region of the sub-critical core assembly. Thus, the IEC replaces both the accelerator system and spallation target by either a central neutron source or by multiple modular sources configured as elements within the 'standard' core assembly. This provides flexibility in design of the core and in flux profile control. Most importantly, these small units can be produced at a lower cost than the accelerator-target system. Considerable research on the IEC concept has already been carried out on a laboratory scale. However, a key remaining issue concerns the ability to achieve the high neutron rates required using the small volume units that are envisioned. Also, there are engineering issues such as the high-voltage feed-throughs, which will require improved technology to prevent unwanted arcing in the intense radiation fields encountered in the reactor core. Ongoing IEC research aimed at the higher neutron yields required is described here.