Effects of Hydrogen Redistribution at High Temperatures in Yttrium Hydride Moderator Material

Abstract

Advanced materials development, manufacturing, and modeling capabilities for innovative reactor designs support nuclear security and mission-focused science through enhanced technology for safer and more efficient and secure production of nuclear energy. The high temperature moderator material yttrium hydride poses a significant enhancement in small reactor design by thermalizing (slowing down) neutrons and decreasing the required fuel mass for a system. The research presented here supports understanding hydrogen distribution in yttrium hydride through: (1) the development of neutron-based hydrogen imaging and crystallographic characterization that allows us to understand fundamental diffraction behaviors and to observe changes in hydrogen distribution as a function of temperature and (2) subsequent neutron multiplication (reactivity) effects of changes in hydrogen distribution using measurement-based cross sections in a sample microreactor design. The main conclusions from the work are that: (1) hydrogen does not redistribute significantly below temperatures of 800°C in yttrium hydride and (2) hydrogen redistribution affects the reactivity slightly but not significantly.

Hydrogen and its detection in fusion and fission nuclear materials – a review

“…Relatively little research has been performed on yttrium hydride moderators over the elapsing decades until recently and consequently they remain at low technology readiness. Yttrium hydride samples were recently irradiated at 600, 700, and 800˚C in the Advanced Test Reactor (ATR) [33] and the High Flux Isotope Reactor [34] to quantitatively investigate hydrogen stability following neutron irradiation as well as perform comprehensive PIE to measure thermomechanical and microstructural properties of irradiated YH [35]. Hydrogen concentration in the irradiated samples will be measured using inert gas fusion, mass balance, and qualitatively using x-ray diffraction, each of which are summarized in Table 3.…”

Versatile Heat Transfer Module

“…All the components of the AMM/VHTM consist of nuclear materials that either have been examined or are being intensively investigated. For example, hydride moderators were well studied in Aircraft Nuclear Propulsion (ANP) project [8] and are currently investigated under Microreactor Program [9] and TCR program [10]; SiCf/SiC cladding has been regarded as promising candidate for both enhanced accident tolerant fuels [11] for light water reactors (LWRs) as well as gas cooled fast reactors (GFRs) [12]; Nb based alloys were selected as cladding materials for uranium nitride based space reactors fuel solution [13]. However, the main challenges to adopt these innovative technologies are assembling and demonstration of the comprehensive system.…”