Development of a fast neutron imaging system for investigating two-phase flows in nuclear thermal–hydraulic phenomena: A status report

•Development of a novel fast neutron imaging system for two-phase flows in fuel bundles.•Novel D–D fusion neutron generator with small emitting spot for imaging.•Dedicated fast neutron imaging detector based on plastic scintillator and SiPM.•Novel proton recoil converter coupled with THGEM readout as imaging detector.

The present paper gives an overview of the status of an ongoing project aiming at the development of a fast neutron imaging system for investigating two-phase flows primarily in the context of nuclear fuel bundle development. Other potential subjects for investigations include steam explosions for severe accident research and liquid metal two-phase flows for Gen IV reactor systems. The project is carried out in the form of a feasibility study that should enable estimation of the ultimate imaging capabilities achievable. The imaging system used in the feasibility study consists of a compact, deuterium–deuterium fusion based neutron generator and dedicated imaging detectors. For the latter two promising concepts are developed in parallel: one is based on an array of plastic scintillators coupled with silicon photomultipliers, the other on a special multi-foil recoil proton converter coupled to a position sensitive charge readout using a micro pattern gas detector.