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Pre-conceptual Design Activities of the NIST Neutron Source: Preliminary Layout of Cold and Thermal Neutron Instruments



Jeremy Cook, Charles F. Majkrzak, Hubert King, Dan Neumann


This report is relevant to the eventual replacement of NIST's NBSR research reactor with a new NIST research reactor – the NIST Neutron Source (NNS) - destined to provide enhanced neutron research opportunities for the US into the future. The report outlines preliminary studies undertaken to assess possible cold and thermal beam and instrument layouts for a pre-conceptual design of the NNS. It makes use of a starting wish list of cold and thermal instruments (outlined in Appendix A) and their estimated footprints and accommodates those requiring end-positions, allowing for instrument accessibility. 16 cold neutron guide tubes in a curved-straight geometry (with no direct line-of-sight to the source from their exits) are assumed to conduct the cold neutron beams in opposing directions from two cold neutron sources into two neutron guide halls. The thermal neutron beams, possibly using thermal neutron guides to locate more instruments further from the reactor face, emerge approximately tangentially to the cold neutron beams. In both cases, the beams are tangential to the fuel, to limit acceptance of unscattered fast neutrons. The curvature and reflective coatings of the cold neutron guides are manufacturable with current technology and chosen to provide high cold neutron flux with low short wavelength contamination and a characteristic wavelength of 0.3 nm (3 Å) for all 16 curved guide sections. Further improvements, optimizations, and the possibility to accommodate an increased number of instruments will be explored later as the NNS design evolves. This technical note is part of a series of notes describing preliminary analyses and planning for the pre-conceptual design of a reactor to replace, in due course, the National Bureau of Standards Reactor (NBSR) at the NIST Center for Neutron Research. The replacement reactor, dubbed as the NIST Neutron Source (NNS), is currently planned to be a 20 MW pool-type compact core cooled and moderated by H2O and fueled with high-assay low-enriched U-10Mo. The core consists of nine fuel assemblies in a 3x3 square lattice encased in a chimney and surrounded by a D2O-filled reflector tank that contains two LD2 cold sources on opposite sides of the core.
Technical Note (NIST TN) - 2280
Report Number


Cold Neutrons, Cold Neutron Sources, Neutron Guides, Neutron Instrumentation, Neutron Research, Research Reactors, Thermal Neutrons


Cook, J. , Majkrzak, C. , King, H. and Neumann, D. (2024), Pre-conceptual Design Activities of the NIST Neutron Source: Preliminary Layout of Cold and Thermal Neutron Instruments, Technical Note (NIST TN), National Institute of Standards and Technology, Gaithersburg, MD, [online],, (Accessed April 19, 2024)
Created February 12, 2024, Updated March 11, 2024