Progress towards Operation of a Deuterium Cold Neutron Source at the NCNR

Abstract

The NIST Center for Neutron Research (NCNR) operates a 20 MW research reactor that produces neutrons for a suite of 30 neutron scattering instruments. 70% of these instruments use cold neutrons (E<5 meV), which are moderated by two separate cold neutron sources. The cold moderator for both sources is liquid hydrogen (LH 2 ), which is in turn cooled by a recently commissioned 7 kW, 14K helium refrigerator. NCNR plans to replace the larger cold source with a new one operating with liquid deuterium (LD 2 ). This report focuses on progress towards the upgrade to liquid deuterium, and options to address the particular challenges of designing and operating a cooling system that simultaneously supports operation with both LH 2 and LD 2 .

Liquid deuterium cold source concept for the NIST neutron source

“…The overall CNS configuration follows a well-established pattern that has worked successfully in several other cold neutron source facilities [13], [14], [15]. The concept includes a moderator cryostat containing LD2 for moderating the neutron flux from the reactor, a deuterium/helium heat exchanger that reliquefies deuterium vapor returning from the cryostat, a helium cryoplant to provide cold helium to the deuterium/helium heat condenser heat exchanger, a ballast vessel to hold the deuterium vapor when the system is warm, a helium containment surrounding the entire deuterium system to provide a safety barrier between the deuterium and surroundings, and interconnecting piping and controls.…”