This paper presents the design and analysis of the Hydrogen Transfer Lines (HTL) in the Spallation Neutron Source Facility (SNS), Oak Ridge National Laboratory in Oak Ridge, Tennessee. SNS is a Neutron Accelerator providing intense pulsed neutron beams for scientific research into the behavior of materials. The use of supercritical Hydrogen provides moderation of these neutron beam lines. This is facilitated by the HTL, which consists of six coaxial tubes transporting supercritical hydrogen to and from the Moderators surrounding the Mercury Target inside the Core Vessel (CV). Each Hydrogen line is surrounded by a vacuum tube in order to preserve the supercritical Hydrogen temperature of −425°F (−254° C/19 K). An inert Helium tube and a Water Jacket surround the Outer Vacuum Jacket.

The Hydrogen boundary is considered the primary containment boundary, with the vacuum tubing being the secondary containment boundary both considered to be safety significant. The HTL assembly tubing must be qualified as Performance Category 3 to the requirements of Department of Energy Standard 1020-1994 for Natural Phenomena Hazards. This requires a detailed dynamic analysis. The HTL must also be qualified to ASCE 43-05 for Limit State consideration for abnormal events and ASME B31.3 for sustained and occasional (upset) loadings. The design basis includes consideration of normal sustained loadings such as deadweight and pressure, as well as thermal expansion/contraction, a Design Basis Earthquake (DBE) with associated Anchor Movements (SAM) and the potential physical interaction between coaxial tubes. Intermittent spacers are provided between some of the tubes, providing a functional interspace between the Hydrogen tubing and the Vacuum Jackets. The analytical methodology involves supplementing unaddressed criteria per ASME B31.3 thus requiring the application of more detailed rules found in ASME Section III, NC-3600, ASCE/SEI 43 – 05 as well as Regulatory Requirements such as USNRC Regulatory Guide 1.61 and 1.92. To assess the potential of a postulated failure of the primary Hydrogen boundary inside the Core Vessel, NUREG 0800, Section 3.6.3, Leak-Before-Break Evaluation Procedures are employed.

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