The Transient Reactor Test (TREAT) facility is able to test the performance of nuclear fuels and materials under power excursions. Very-brief power bursts meant to simulate postulated Reactivity-Initiated Accidents (RIA) in light water reactors are of keen interest to DOE and industry for the development of advanced nuclear fuels. TREAT is innately capable of performing RIA-type pulse transient excursions. However, the duration (or width) of these excursions is longer than desired for better simulation of RIAs. With some modification, it should be possible to shorten the TREAT pulse-width, thereby allowing investigation of RIAs. To shorten the TREAT pulse-width, it is proposed that a He-3 injection device be integrated into TREAT to clip the pulse. This system has been termed the Helium-3 Enhanced Negative Reactivity Insertion (HENRI) system. Currently, the Full-Width at Half Maximum (FWHM) duration of a TREAT pulse is no shorter than 72 ms. To achieve a desired pulse width in the range of ~40-50 ms, there is a need to rapidly inject He-3 into chambers in the TREAT core.

The project involved the design, construction and testing of an out-of- pile prototype gas injection system (assumedly using conventional helium 4 He), comparison of the empirical results with necessary refinements to the predictive model, and publication of the results.