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Status of the Liquid Deuterium Cold Neutron Source for the NIST Research Reactor



Robert E. Williams, Michael Middleton, Paul Kopetka, J. Michael Rowe, Paul C. Brand


The NBSR is a 20 MW research reactor operated by the NIST Center for Neutron Researcher (NCNR) as a neutron source providing beams of thermal and cold neutrons for research in materials science, fundamental physics and nuclear chemistry. A large, 55 cm diameter beam port was included in the design for the installation of a cold neutron source, and the NCNR has been steadily improving its cold neutron facilities for man than 25 years. Monte Carlo simulations have shown that a liquid deuterium (LD2) source will provide an average gain of 1.5 between 4 A and 9 A with respect to the existing liquid hydrogen cold source, and a gain of 2 at the longest wavelengths. The conceptual design for the LD2 source will be presented along with the current status of the project. To achieve these gains, a large volume (35 litres) of LD2 is required. The expected nuclear heat load in this moderator and vessel is 4 kW. A new, 7 kW helium refrigerator is being installed to provide the necessary cooling capacity. It is expected that acceptance testing will be completed later this year. The source will operate as a naturally circulating thermosiphon, very similar to the horizontal cold source in the high flux reactor at the Institut Laue-Langevin in Grenoble. A condenser will be mounted on the reactor face about 2 m above the source providing the gravitational head to supply the source with LD2. The system will always be open to a 16 m3 ballast tank to store the deuterium at 4-5 bar when the refrigerator is not operating; this provides a passively safe response to a refrigerator trip. It is expected the source will operate at 23 K, the boiling point of LD2 at 1 bar. All components will be surrounded by a blanket of helium to prevent the possibility of creating a mixture of deuterium and air. A preliminary design for the cryostat assembly, consisting of the moderator chamber, vacuum jacket, helium containment and a heavy water cooling water jacket, has been completed. The ballast tank and a pair of condensers (one spare) have been procured. Initial bids for the cryostat assembly were way over budget, however, and NCNR is seeking additional funding. It is now expected that installation of the LD2 source will be delayed until at least 2021. Funding for the refrigerator and the cold source upgrade has been granted by the National Nuclear Security Administration of the Department of Energy as a mitigation strategy to offset the anticipated 10% loss in neutron flux when the NBSR is converted to low-enriched uranium (LEU) fuel.
Conference Dates
March 13-17, 2016
Conference Location
Conference Title
European Research Reactor Conference


cold neutrons, liquid deuterium, cryogenic refrigerator, safety


, R. , , M. , Kopetka, P. , , J. and DeRose, P. (2016), Status of the Liquid Deuterium Cold Neutron Source for the NIST Research Reactor, European Research Reactor Conference, Berlin, -1, [online], (Accessed June 1, 2023)
Created April 28, 2016, Updated February 19, 2017