[en] The major elements which must be considered in the design of a cold neutron source are identified, and possible solutions are presented. Alternative solutions are illustrated by examples from existing and planned cold neutron sources

[en] The design process for the series of cold neutron sources installed at NIST is presented, with particular emphasis on the reason for the decisions and choices made. These developments are used to illustrate some of the general principles of CNS design

[en] The NBSR is a 20 MW research reactor operated by the NIST Center for Neutron Research (NCNR) as a neutron source providing beams of thermal and cold neutrons for research in materials science, fundamental physics and nuclear chemistry. A large, 550 mm 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 more than 25 years. Monte Carlo Simulations have shown that a liquid deuterium (LD₂) source will provide a gain of 1.5 to 2 for neutron wavelengths between 4 A and 10 A with respect to the existing liquid hydrogen cold source. The conceptual design for the LD₂ source will be presented. To achieve these gains, a large volume (35 litres) of LD₂ is required. The expected nuclear heat load in this moderator and vessel is 4000 W. A new, 7 kW helium refrigerator is being built to provide the necessary cooling capacity; it will be completely installed and tested early in 2014. 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 (ILL) 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 500 kPa when the refrigerator is not operating, and providing a passively safe response to a refrigerator trip. It is expected the source will operate at 23 K, the boiling point of LD₂ at 100 kPa. All components will be surrounded by a blanket of helium to prevent the possibility of creating a flammable mixture of deuterium and air. A design for the cryostat assembly, consisting of the moderator chamber, vacuum jacket, helium containment and a heavy water cooling water jacket, has been completed and sent to procurement to solicit bids. It is expected that installation of the LD₂ cold source will begin in April of 2016. 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