A Multi-Purpose Test Station to Characterize Fast Neutron Detectors for the Transient Reactor Test Facility (TREAT) Fuel Motion Monitoring System

The Transient Reactor Test Facility (TREAT) at Idaho National Laboratory is an aircooled, graphite-moderated reactor designed to evaluate reactor fuels and structural materials under conditions that simulate various types of transient overpower and under-cooling situations in a nuclear reactor. Fuel meltdowns, metal-water reactions, thermal interaction between overheated fuel and coolant, and the transient behavior of ceramic fuel for high-temperature systems can be studied. A key instrument that monitors fuel motion as these events take place is t he fast neutron hodoscope. The hodoscope is designed to allow for pre-, during-, and post-transient imaging of fuel in a test loop in the center of the reactor’s core. The preferred technique for imaging is detection of fast neutrons produced by fission in the test fuel, travelling unmoderated through a core slot and then a multi-slot collimator to a 360detector array collinear to the collimator channels. Due to the age of the instrument, a refurbishment of the hodoscope’s fast neutron detection capability is necessary. Described here is a Multi-Purpose Test Station (MPTS) that was designed to simultaneously qualify and characterize up to eight photo-multiplier tubes using a distributed light source. The MPTS also provides a means to characterize up to eight fast neutron detector assemblies consisting of ZnS(Ag) scintillators coupled to photomultiplier tubes, using a radiologic source.